serum carotenoids and tocopherols and severity of nuclear and cortical opacities

Articles

Serum Carotenoids and Tocopherols and Severity ofNuclear and Cortical Opacities

Julie A. Mares-Perlman,* William E. Brady* Barbara E. K. Klein,* Ronald Klein,*Mori Palta,f Phyllis Bowen,\ and Maria Stacewicz-Sapuntzakis%

Purpose. To determine whether higher levels of individual carotenoids and tocopherols in theserum are related to less severe nuclear and cortical opacities within the general population.

Methods. Levels of individual carotenoids and tocopherols in the serum were determined in400 randomly selected persons aged 50 to 84 years participating in the Nutritional Factors inEye Disease Study of Beaver Dam, Wisconsin. Severity of nuclear and cortical opacities wasassessed from lens slit lamp and retroillumination photographs taken at the same time.Relationships between serum levels of nutrients and prevalence of these opacities were evalu-ated using logistic regression analysis accounting for known possible confounders.

Results. Higher levels of individual or total carotenoids or a-tocopherol in the serum werenot associated with less severe nuclear or cortical opacities overall. However, associationsdiffered between men and women and within specific population subgroups. A significanttrend for lower odds for either type of opacity with increasing levels of /3-carotene in theserum was observed in men. For nuclear sclerosis, this protective association with /̂ -carotenewas found in younger but not older men. Higher levels of three other carotenoids (a-carotene,/?-cryptoxanthin, and lutein) in serum were significantly related to lower odds for nuclearsclerosis only in men who smoked. In contrast to these inverse associations observed in somesubgroups, higher levels of some carotenoids and a-tocopherol often were direcdy associatedwith nuclear sclerosis, particularly in women.

Conclusions. Higher levels of carotenoids and tocopherols are not consistently associated withless severe opacities in the general population. Invest Ophthalmol Vis Sci. 1995;36:276-288.

Opacities in the nuclear and cortical region be-come more common with age. Identification of fac-tors that delay their occurrence may eventually re-duce the number of cataract extractions performedand might also help identify factors that contributeto the slowing of other degenerative processes ofaging. Higher dietary levels of nutrients with rolesin oxidant defense systems may protect against lensopacification.1'2 Studies in experimental animals us-

Fnrn the * Department of Ophthalmology and Visual Sciences, University ofWisconsin Medical School, Madison, the f Department of Preventive Medicine,University of Wisconsin, Madison, Wisconsin, and the tDepartment of Nutritionand Medical Dietetics, University of Illinois at Chicago, College of Associated HealthProfessions, Chicago, Illinois.Supported by National Eye Institute grants EYO80I2 (/AMP) and EYO6594 (RK,BEKK).Submitted for publication January 31, 1994; revised July 14, 1994; acceptedSeptember 13, 1994.Projnietary interest category: N.Reprint requests: Julie A. Mares-Perlman, Department of Ophthalmology and VisualSciences, University of Wisconsin-Madison, 610 N. Walnut Street, 405 WARF,Madison, WI53705-2397.

ing extreme variations in nutrient intake supportthis notion. Supplementation of experimental ani-mals with vitamin E3 or vitamin C,4'5 which can func-tion as antioxidants, has been shown to slow cata-ractogenic processes. Results of studies in humanpopulations have been conflicting. Dietary levels ofsome antioxidant nutrients have been found to berelated to the occurrence of opacities in one6 butnot another7 previously published study.

Detection of correlations with dietary levels ofnutrients may be hampered by inability to accountfor factors that alter absorption or utilization of nu-trients. There is great individual variability in ab-sorption of some dietary nutrients such as carot-enoids.8 Therefore, serum levels of some nutrientsmay give a more accurate reflection of the true levelof nutrients available to tissues. Relationships be-tween opacities and serum levels of antioxidant nu-trients have been studied. However, as with dietarystudies, results are inconsistent.9'10"13

276Invesiigaiive Ophthalmology & Visual Science, February 1995, Vol. 36, No. 2Copyright © Association for Research in Vision and Ophthalmology

Lens Opacities and Antioxidant Nutrients in Serum 277

In previous studies, factors associated with themost severe levels of opacities have been evaluated.The study of less severe opacities may permit evalua-tion of early cataractogenic factors before the pres-ence of comorbid conditions within the eye or otherorgans influence behavior.

Relationships between lens opacities and levels ofindividual carotenoids in the diet or serum, other than/3-carotene, have not been studied. Several other ca-rotenoids exist in serum in quantities more abundantthan /3-carotene.14 All have the potential to functionas antioxidants.15 This report describes relationshipsbetween lens opacities and levels of the two most abun-dant tocopherols and the five most abundant carot-enoids in human serum in the general population.Concordance of relationships with levels of nutrientsin both diet and serum are also evaluated.

MATERIALS AND METHODS

Study Population

From the Beaver Dam Eye Study, 400 people (aged50 to 84 years) with gradable lens photographs, whowere also participants in the Nutritional Factors in EyeDisease Study, were randomly chosen to be includedin the present study. The number of subjects was cho-sen to allow an 80 to 90% chance for detecting rela-tionships between carotenoids and severity of nuclearsclerosis (if one did exist) with odds ratios betweenextreme quintile levels of 1.2 or greater. Recruitmentand participation in the Nutritional Factors in EyeDisease Study16 and the Beaver Dam Eye Study havebeen described in detail elsewhere.17 The Beaver Damcohort includes the entire population of persons aged43 to 84 years of age residing in Beaver Dam, Wiscon-sin identified by a private census in 1987, who werewilling and able to participate in the study (n = 4926).Participants in the Nutritional Factors in Eye DiseaseStudy were a 50% random sample of the free-livingBeaver Dam Eye Study participants who were willingand able to participate (n = 2152). The sample fromwhich participants were randomly selected for thepresent study excluded 74 participants who were apha-kic (10 persons), had intraocular lenses in both eyes(30 persons), or whose photographs were otherwisenot gradable (34 persons). This study followed thetenets of the Declaration of Helsinki and was approvedby the University of Wisconsin Human Study ReviewBoard. Informed consent was obtained from each par-ticipant.

Examination and Lens Photography

The procedures used for lens photography during theBeaver Dam Eye Study examination have been de-tailed elsewhere.18 Briefly, photographs were made of

the lens after assessing anterior chamber depth anddilating pupils with one drop each of 1 % tropicamideand 2.5% phenylephrine. A Topcon SL5 Slit Lampcamera (Paramus, NJ) with the illuminating beam at45° to the viewing system and specially designed fixa-tion targets for each eye was used for photographsfor assessing nuclear sclerosis. Cortical opacities werephotographed with a retroillumination camera (CR-T, Neitz, Torrance, CA) specifically modified for thisstudy. Photographs were graded for the severity of lensopacities according to standard protocols. Graderswere masked to subject characteristics. Photographscorresponding to each eye, for each subject, were sep-arated and graded independently.

Nuclear sclerosis was graded on a five-step scaleby comparing each photograph with a set of standardphotographs. Because few subjects had nuclear sclero-sis at severity level 5, subjects with nuclear sclerosis atlevels 4 and 5 were combined for the purposes of theseanalyses. Because early nuclear opacities (level 2 or 3)were present in the majority of participants sampled,a four-level nuclear opacity score ranging from 1 to4/5 was employed. Cortical opacities were defined aspresent when opacities occupied 5% or more of thecortical area photographed. Data for the worse eye ofeach participant were used in analyses.

A standardized interview about social and demo-graphic characteristics and medical history was admin-istered at the time of the eye examination. This sourceprovided data on the potentially confounding factorsof heavy alcohol use, smoking, diabetes, sunlight expo-sure, body mass index, and education. A positive his-tory of heavy drinking was defined as reporting anaverage current consumption of four or more drinksper day or a positive response to the question "Hasthere ever been a time in your life when you drankfour or more alcoholic beverages daily?" The numberof pack-years smoked was calculated as the number ofpacks of cigarettes smoked per day times the totalnumber of years the participant reported smoking. Apositive history of diabetes was defined as a historyof diabetes mellitus treated with either insulin, oralhypoglycemic agents, and/or diet, or high levels ofboth casual blood glucose (>11.1 mmol/1) and gly-cated hemoglobin (>2 SD from the mean) in theblood.19 Average ambient ultraviolet-B sunlight expo-sure was estimated as described elsewhere.1*0 Heightand weight measurements were made at the examina-tion (with clothing, but without shoes) to calculatebody mass index (wt/ht2).

Laboratory Analyses

Blood specimens were collected from nonfasting parti-cipants at the time of examination. An aliquot portionof serum from these specimens was used immediatelyfor determination of total cholesterol.21 Remaining

278 Investigative Ophthalmology & Visual Science, February 1995, Vol. 36, No. 2

serum was stored at — 80°C in cryogenic vials with Orings for up to 4.5 years until shipment on dry icefor laboratory analysis. Serum, a-carotene, /?-carotene,lutein/zeaxanthin, lycopene, /3-cryptoxanthin, a-to-copherol, and y-tocopherol were determined by highperformance liquid chromatography.14

Assessment of Diet and Supplement Use

Usual daily intake of individual and total carotenoids,vitamin A and vitamin E were determined from foodsand supplements using responses to a diet history in-terview administered in person in the participants'homes approximately 1 month after eye examinations.Dietary habits during the preceding year were que-ried. The questionnaire was a modification of version2.1 of the National Cancer Institute Diet History Ques-tionnaire developed by Block.22 A detailed descriptionof the questionnaire and subsequent nutrient analyseswas given in a previous report.16 The relative validityof nutrient data in this population using this methodhas also been described.23

Statistical Analyses

Participants were categorized into quintiles for con-centrations of individual carotenoids and tocopherolsin the serum and for the sum of all measured carot-enoids in the serum. Quintile rank for estimated usualintake of these nutrients in the diet (per 4.18 MJ or1000 kilocalories) was also computed. Odds ratioswere computed using ordinal logistic regression, ad-justing only for age, for each quintile compared withthe first quintile. Linear trend was assessed in analysessubstituting quintile median levels of nutrients forquintile rank.

The odds ratio for severity of nuclear opacitiesapproximates the risk of being one step higher on afour-step severity scale. This method is valid only whenthe odds do not vaiy significantly among levels of se-verity. This was confirmed by the finding of no signifi-cant differences (P > 0.05) in the proportional oddstest, indicating that the logistic regression models fitthe data in this four-level format.

Variables identified in this or other studies to berelated to both the serum nutrient levels2425 and nu-clear or cortical opacities7'8'20'26'27 were evaluated aspossible confounders. For nuclear sclerosis, these in-cluded gender, serum cholesterol (as a marker forserum lipids), smoking, education, body mass index,heavy drinking, beer drinking, multivitamin use (yes/no), and the use of any supplements containing vita-min A or vitamin E. For cortical opacities, these in-cluded gender, smoking, heavy drinking, multivitaminuse (yes/no), use of any supplements containing vita-min A or vitamin E, diabetes, and average ambientultraviolet-B exposure. Variables that altered odds ra-tios for at least one nutrient by 10% or more were

included in the final adjusted logistic regressionmodel.

Interactive effects of several variables were testedas effect modifiers including gender, multivitamin use,age, and smoking. When significant interactive effectswere identified, results are presented separately forrelevant subgroups. In such subgroups, quintile levelsof serum nutrients were redefined for each subgroupevaluated.

Additional analyses were conducted to determinewhether associations with serum nutrients were similarfor cortical and nuclear opacities considered sepa-rately and to determine whether results for one typewere independent of possible influences of differentdistributions of another type of opacity in comparisongroups. Analyses of each opacity were stratified bypresence or absence of severe nuclear opacities (levels4 or 5) or presence or absence of cortical opacities(which cover greater than 5% of the grading areas inlens photographs).

RESULTS

Sample Characteristics

The distribution of nuclear and cortical opacities andcharacteristics of persons in this sample are given inTable 1. Persons with more severe nuclear sclerosisand cortical opacities were more likely to be older.The proportion of men who smoked or had a historyof smoking or a history of heavy drinking was higherthan women within each category of nuclear sclerosis.Supplement use was less common in men.

Mean levels of a- and /3-carotene, /3-cryptoxan-thin, and total carotenoids determined by analysis ofvariance (adjusting for age) were higher (P < 0.05)in women than in men. The data in Table 2 indicatethese carotenoids are generally higher in women ateach quintile level. Similar gender-related differencesfor a-tocopherol existed but means were not signifi-cantly different (P > 0.05).

Correlations between carotenoid levels in plasmawere tested in men and women. Levels of individualcarotenoids were significantly correlated (P < 0.05)except for lycopene and cryptoxanthin in women.However, correlation coefficients varied substantially.In men, Spearman correlation coefficients rangedfrom 0.21 for lycopene versus a-carotene to 0.75 fora-carotene versus /3-carotene. In women, correlationsranged from 0.13 for lycopene versus /3-cryptoxanthinto 0.75 for a-carotene versus /3-carotene.

Nuclear Sclerosis and Carotenoids

In logistic regression analyses, adjusting only for age,persons with serum levels of total carotenoids in thehighest quintile were more likely to have more severe


TABLE i. Percent of Sample With Indicated Characteristics by Opacity Level and Type

Age (years)Women

50-5960-6970-7980-86

Men50-5960-6970-7980-86

Cortical Opacities PresentWomenMen

Nuclear Opacities PresentWomenMen

Education (years)*Women

<12>12

Men<12>12

History of Diabetes*Women (n = 217)Men (n = 179)

Smokers (1988-90)*WomenMen

History of Smoking*WomenMen

History of Drinking*^WomenMen

UseJ of Supplements ContainingBeta-carotene*

WomenMen

Vitamin A*WomenMen

Vitamin E*WomenMen

Level 1(n = 11)

45

802000

100000

00

031

3020

00

130

51100

020

00

021

1937

Nuclear Sclerosis

Level 2(n = 153)

47

5440

60

573760

811

1526

4121

85

1221

3666

321

137

3426

3626

Level 3(n = 153)

59

2336347

2144296

2617

3419

2832

84

1925

3975

341

95

3224

3631

Level 4(n = 83)

64

8195519

3305017

4713

3219

3321

83

1542

3087

839

43

3313

3917

P value

0.05

<0.001

<0.001

<0.001

0.080.30

0.390.49

0.84 .0.80

0.510.06

0.610.24

0.340.03

0.180.64

0.760.34

0.700.64

Cortical Opacity

Absent(n = 320)

52

393721

2

3938185

——

17171

2621

3624

54

1923

3976

531

86

2923

3427

Presenti (n = 80)

69

6195422

213342

4

—

4617

2823

2630

188

737

2763

228

94

4224

4324

P value

.005

<.001

.04

—

<.001.53

.78

.76

0.27.59

.01

.35

.11

.15

.28

.17

.65

.78

.77

.77

.09

.92

.25

.74

* Age-adjusted.f Heavy drinking is defined as four or more drinks per day.% Use defined as at leasl weekly.

nuclear sclerosis compared with those in the lowestquintile (odds ratio 1.72; 95% confidence interval[CI] 0.90, 3.20). However, the odds ratio was not statis-tically significant. Risk for nuclear sclerosis was alsonot associated positively or negatively with lower levelsof individual carotenoids in these crude analyses (datanot shown).

When potential confounding factors of gender,serum cholesterol (as a marker for serum lipids),smoking, education, body mass index, heavy drinking,beer drinking, multivitamin use, and use of any sup-plements containing vitamin A were investigated, onlyserum cholesterol and gender affected the models inimportant ways. The addition of serum cholesterol


TABLE 2. Median Nutrient Levels in Serum by Gender* in Adults50-86 Years of Age

Nutrient (/imol/l)

CarotenoidsAlpha-carotene

WomenMen

Beta-caroteneWomenMen

LycopeneWomenMen

Beta-cryptoxanthinWomenMen

LuteinWomenMen

Total CarotenoidsWomenMen

Vitamin Ea-tocopherol

WomenMen

y-tocopherolWomenMen

1

0.030.02

0.130.09

0.180.21

0.070.04

0.160.14

0.790.69

18.216.9

2.82.9

2

0.060.04

0.230.16

0.350.36

0.120.09

0.210.21

1.100.99

23.520.5

4.85.0

Quintile

3

0.090.06

0.340.22

0.460.46

0.180.12

0.270.26

1.461.21

26.824.6

6.06.7

4

0.120.08

0.480.32

0.600.59

0.240.18

0.340.31

1.811.45

32.928.5

7.98.4

5

0.180.14

0.780.52

0.810.81

0.370.31

0.450.43

2.201.93

46.537.8

11.710.9

* n = 220 women; n = 180 men.

altered the /^-coefficient for some carotenoids and to-copherols and was therefore retained in the adjustedmodel. After controlling for these factors, a significanttrend for higher odds for nuclear sclerosis was presentwith increasing levels of total carotenoids in serum(Table 3). The patterns for individual carotenoidswere similar for all but /3-cryptoxanthin.

There were significant interactions between gen-der and levels of serum (P < 0.10) carotenoids. Thedifference in odds ratios for linear trend was signifi-cant for a-carotene (P= 0.06), /3-cryptoxanthin, (P =0.03), lutein (P = 0.02), and total carotenoids (P =0.02). Consequendy, data were analyzed separately inmen and women.

Contrary to results in the overall sample, adjustedodds ratios in men were <1 for all carotenoids exceptlycopene (Table 3). However, these relationships werenot statistically significant. In women, odds ratios > 1 ,indicating adverse associations, were observed for highserum levels of all carotenoids. Relationships were ei-ther statistically significant or marginally significant (P= 0.05 to 0.10) for all individual carotenoids. Furtheradjustment for potential nondietary confoundersadded singly or together did not influence odds ratiosin men or women.

One explanation for the observation of more se-vere nuclear sclerosis associated with higher serumlevels of carotenoids in women could be that knowl-edge of this opacity may have altered their behaviorin ways that would increase blood carotenoid levels.However, women with nuclear sclerosis greater thanlevel 3 who had been told they had cataracts by theirphysicians (mean [±SD] 1.61 ± 0.54 //mol/1; n = 20)had similar levels of total carotenoids compared withthose who had not been told (mean [±SD] 1.64 ±0.64/Limol/1; n = 33).

In women, the presence of more severe nuclearopacities was related to the presence of cortical opacities(Table 1). However, stratification by presence (n = 166)or absence (n = 56) of cortical opacities did not influ-ence direct relationships between nuclear sclerosis andserum levels of carotenoids or tocopherols. Similarly, inmen, odds ratios for nuclear sclerosis were similar inthose without cortical opacities (n = 156) as they werein the sample overall (data not shown). There were toofew men (n = 24) with cortical opacities to test relation-ships with nuclear opacities in this subgroup.

The concordance in result when using serum ver-sus dietary levels of nutrients was evaluated. Averagelevels of carotenoids in the diet (individual and total)


TABLE 3. Adjusted Odds Ratios* for More Severe Nuclear Sclerosisin the Highest Versus Lowest Quintile of Serum Nutrient inAdultsf 50-86 Years of Age

Carotenoids

Alpha-caroteneEntire SampleWomenMen

Beta<aroteneEntire SampleWomenMen

LycopeneEntire SampleWomenMen

Beta-cryptoxanthinEntire SampleWomenMen

LuteinEntire SampleWomenMen

TotalEntire SampleWomenMen

Tocopherols

a-tocopherolEntire SampleWomenMen

•y-tocopherolEntire SampleWomenMen

OddsRatio

1.142.620.60

1.542.800.86

1.962.261.69

0.841.560.56

1.454.090.71

1.903.950.55

2.131.473.74

0.610.590.53

95% Confidence Interval

0.61,1.12,0.23,

0.81,1.21,0.33,

0.98,0.91,0.56,

0.45,0.68,0.22,

0.75,1.67,0.27,

0.99,1.65,0.20,

1.05,0.57,1.25,

0.32,0.24,0.20,

2.146.131.55

2.916.482.28

3.955.635.14

1.573.571.45

2.8010.031.89

3.669.471.49

4.343.8211.2

1.191.461.45

TrendP Valuet

0.360.090.34

0.120.060.88

0.040.040.45

0.780.080.20

0.130.0060.93

0.030.0020.52

0.050.330.14

0.040.110.11

* Adjusted for age and level of cholesterol in the serum.t « = 220 women; re = 180 men.X Tested across five quintiles using quintile medians.

were generally higher in men and women in thehigher quintiles for serum carotenoids (data notshown). Thus, as expected, relationships between di-etary levels and nuclear sclerosis were similar to thoseobserved for serum levels (Table 4).

Interactions by factors that could modify nutri-tional modification of risk for nuclear sclerosis weretested. Multivitamin use did not influence associa-tions. Relationships generally remained inverse andnonsignificant in men who used multivitamin supple-ments and in those who did not (data not shown).Similarly, relationships in women remained direct re-gardless of multivitamin use.

Relationships were sometimes influenced by age.A significant interaction between age (years) and fi-

carotene levels in the highest versus lowest quintilewas noted in men (P = 0.005). Odds ratios (95% CI)for more severe nuclear sclerosis computed with thisinteraction term for men in high versus low quintilesof/3-carotene were 0.20 (95% CI 0.05,0.88) at 55 yearsof age, 1.13 (95% CI 0.42,3.04) at 65 years of age, and6.33 (95% CI 1.21,32.88) at 75 years of age. Significant(P < 0.05) age interactions were not evident for othercarotenoids.

Smoking status at the time of interview did notalter the direct association in women (Table 5). How-ever, inverse relationships were sometimes stronger inmen who smoked: higher serum levels of a-carotene,/?-cryptoxanthin, and lutein were associated with lesssevere nuclear sclerosis in smokers (Table 5).


TABLE 4. Adjusted* Odds Ratios for NuclearSclerosis in the Highest Versus LowestQuintile for Usual Daily Intake ofNutrientsf in the Diet of Adults^ 50 to 86Years of Age

Alpha-caroteneWomenMen



LuteinWomenMen

LycopeneWomenMen

Total CarotenoidsWomenMen

Vitamin EWomenMen

Odds Ratio

2.090.30§

1.310.44

4.10§1.07

1.430.77

1.210.62

1.720.41

1.890.85

95% Confidence Interval

0.87,0.11,

0.56,0.44,

1.72,0.40,

0.61,0.30,

0.52,0.23,

0.74,0.15,

0.82,0.32,

5.040.84

3.101.23

9.762.87

3.372.01

2.791.66

3.991.10

4.352.25

* Adjusted for heavy drinking and pack-years smoking,f Carotenoid intake (fig) per 4.18 MJ (1000/kcal).X n = 220 women; n — 180 men.§ P < 0.05.

Nuclear Sclerosis and Tocopherols

Only levels of y-tocopherol, the tocopherol thoughtto have low biologic vitamin E activity, was inverselyrelated to the severity of nuclear sclerosis (Table 3).The relationship was similar in magnitude and direc-tion in men and women. Levels of a-tocopherol, themost biologically active vitamin E compound, werealso related to nuclear sclerosis, but in the oppositedirection. Persons in the highest versus lowest quintilewere two times more likely to have more severe nu-clear sclerosis (Table 3). In contrast to that observedfor carotenoids, this relationship was similar in menand women. We investigated whether prior knowledgeof the presence of a cataract might explain this rela-tionship. Levels of a-tocopherol were lower, ratherthan higher, in people with (mean [±SD] 33.3 ± 12.6limo\/\; n = 27) than without (mean [±SD] 34.2 ±14.9 /Ltmol/1; n = 56) knowledge of cataract.

Concordance of associations with dietary datawere also evaluated. Age-adjusted dietary and supple-mental levels of vitamin E were generally higher (P< 0.0001) in higher quintiles for serum levels of a-tocopherol. In contrast, higher levels of vitamin E inthe diet were related to lower quintile rank for y-tocopherol (P < 0.0001). Total dietary vitamin E in

these cross-sectional analyses was unrelated to nuclearsclerosis in men and women (Table 4). The positivedirection of the odds ratios persisted in women butnot in men.

Cortical Opacities and Any Cataract

In logistic regression analyses, adjusting only for age,levels of carotenoids or tocopherols in the serum wereunrelated to cortical opacities. Only the addition ofcholesterol and diabetes to the model significantly al-tered regression coefficients. After adjusting for thesecovariates, levels of individual or grouped carotenoidsremained unrelated to cortical opacities (Table 6).

Because odds ratios for men and women weredifferent (P< 0.05) for some carotenoids (/3-caroteneand lycopene), analyses were performed separately bygender. In men, a marginally significant (P = 0.05)trend was observed for lower levels of cortical opacitieswith higher levels of /3-carotene in the serum. Theodds ratio for levels of /^-carotene in the highest versuslowest quintile was 0.28 (95% CI 0.06,1.24). In women,odds ratios were frequently >1 , similar to the resultsobserved with nuclear sclerosis. Women with levels inthe highest versus lowest quintile for the sum of allmeasured carotenoids were almost four times morelikely to have cortical opacities (Pfor trend = 0.01).Similar to observations made for nuclear sclerosis, lev-els of a-tocopherol were directly related to corticalopacities (Table 6). For -y-tocopherol, odds ratios were> 1 as well but were not statistically significant.

Because most persons with cortical opacities alsohave more severe nuclear sclerosis, analyses were re-peated in persons without severe nuclear opacities(levels 4 or 5). In women without severe nuclear opaci-ties (n = 167), odds ratios for all serum nutrientsremained in a similar direction, except for /3-crypto-xanthin for which confidence intervals were wide(odds ratio 0.92, 95% CI 0.23,3.64). Similarly, oddsratios were in similar directions in men without nu-clear cataract (n = 150) as they were in all men (datanot shown).

Because associations were similar for many serumnutrients among opacity types, the associations withpresence of any cataract were considered. In men,but not women, a significant (P = 0.03) trend fordecreased odds for cataract with increasing serumlevel of/0-carotene was observed. In women, consistentwith results for individual opacities, serum levels oftotal carotenoids in the highest versus lowest quintilewere associated with higher risk for cataract.

DISCUSSION

Low levels of carotenoids or a-tocopherol in the serumwere not cross-sectionally related to higher risk fornuclear or cortical opacities in a representative sample


TABLE 5. Odds Ratios* for More Severe Nuclear Sclerosis by Gender and Current SmokingStatus in AdultsJ 50-86 Years of Age

Women

Nutrient (fim/l)

Not Smoking

(n = 184)

Smoking

(n = 36)

Men

Not Smoking

(n = 135)

Smoking

(n = 45)

CarotenoidsAlpha-caroteneMedian serum level in

quintile l:quintile 5Adjusted odds ratio*95% confidence limitsTrend (P value)

Beta-caroteneMedian serum level in

quintile l:quintile 5Adjusted odds ratio*95% confidence limitsTrend (/'value)

LycopeneMedian serum level in

quintile l:quintile 5Adjusted odds ratio*95% confidence limitsTrend (/"value)

Beta-cryptoxanthinMedian serum level in

quintile l:quintile 5Adjusted odds ratio*95% confidence limitsTrend (Pvaluue)

LuteinMedian serum level in


Total CarotenoidsMedian serum level in

quintile l:quindle 5Adjusted odds ratio*95% confidence limitsTrend (P value)

Tocopheroka-tocopherolMedian serum level in

quintile l:quintile 5Adjusted odds ratio*95% confidence limitsTrend (/"value)

7-tocopherolMedian serum level in


0.0:0.21.96

(0.78, 4.91)0.29

0.1:0.81.93

(0.77, 4.81)0.29

0.2:0.83.27

(1.17, 9.13)0.02

0.1:0.41.48

(0.60, 3.64)0.20

0.2:0.53.52

(1.33, 9.27)0.02

0.8:2.23.67

(1.41, 9.54)0.01

0.0:0.213.85

(1.00, 192.80)0.06

0.1:0.517.86

(1.47, 217.16)0.04

0.2:0.70.63

(0.06, 6.81)0.78

0.1:0.315.92

(1.25, 203.47)0.03

0.2:0.47.77

(0.40, 149.66)0.05

0.7:1.9169.66

(5.25, 999.00)0.01

0.0:0.10.91

(0.30, 2.82)0.96

0.1:0.51.94

(0.63, 6.03)0.26

0.2:0.82.13

(0.56, 8.17)0.13

0.1:0.31.13

(0.37, 3.43)0.93

0.2:0.50.82

(0.25, 2.71)0.62

0.7:1.92.32

(0.68, 7.90)0.16

0.0:0.10.27

(0.03, 2.70)0.04

0.1:0.40.37

(0.04, 3.15)0.14

0.2:0.81.29

(0.16, 10.31)0.40

0.0:0.30.04

(0.00, 0.41)0.03

0.1:0.30.17

(0.01, 1.91)0.05

0.7:1.90.37

(0.04, 3.81)0.14

19.1:47.91.52

(0.55, 4.22)0.34

2.9:11.70.56

(0.21, 1.48)0.10

17.5:38.91.06

(0.06, 18.76)0.69

2.2:11.70.31

(0.03, 3.19)0.57

16.5:37.54.33

(1.21, 15.57)0.06

2.9:10.90.55

(0.17, 1.75)0.20

17.0:38.45.49

(0.47, 63.68)0.58

2.9:10.00.42

(0.06, 3.15)0.63

; Adjusted for age and serum cholesterol.


TABLE 6. Adjusted* Odds Ratios for Cortical Cataract and Any Cataract in the HighestVersus Lowest Quintile for Nutrients in the Serum in Adultsf 50-86 Years of Age

Nutrient

Carotenoids

Alpha-caroteneWomenMen


LycopeneWomenMen


LuteinWomenMen

TotalWomenMen

Tocopherols

a-tocopherolWomenMen

y-tocopherolWomenMen

Cortical Cataract

Odds Ratio(95 % Confidence Interval)

0.87 (0.23, 3.25)0.82 (0.20, 3.44)

2.00 (0.57, 6.98)0.28 (0.06, 1.24)

3.21 (0.78, 13.2)0.37 (0.06, 2.36)

1.45 (0.43, 4.90)0.54 (0.08, 3.78)

1.75 (0.49, 6.21)4.84 (0.83, 28.1)

3.26 (0.92, 11.5)0.62 (0.12, 3.20)

2.11 (0.44, 10.06)3.94 (0.59, 26.2)

2.06 (0.55, 7.71)1.30 (0.25, 6.88)

TrendP Value%

0.850.68

0.290.05

0.150.35

0.340.24

0.990.03

0.050.49

0.890.22

0.290.88

Any Cataract

Odds Ratio(95 % Confidence Interval)

1.61 (0.49,5.36)0.45 (0.12, 1.67)

3.53 (1.16, 10.7)0.33 (0.09, 1.20)

2.63 (0.76, 9.04)0.48 (0.10, 2.32)

1.41 (0.48, 4.11)0.38 (0.10, 1.40)

3.30 (1.07, 10.14)1.50 (0.41, 5.50)

4.41 (1.39, 1.399)0.35 (0.09, 1.34)

3.19 (0.89, 11.43)3.95 (0.93, 16.87)

1.25 (0.39, 4.02)1.05 (0.29, 3.77)

TrendP ValueX

0.810.10

0.070.03

0.110.37

0.310.09

0.090.38

0.010.14

0.150.12

0.800.96

* Adjusted for age, serum cholesterol and presence of diabetes.f n = 217 women; 179 men (3 women and 1 man were excluded due to unknown diabetes status).X Presence of cortical opacities or nuclear opacities greater than level 3.

of middle-aged and older-aged adults participating inthe Nutritional Factors in Eye Disease Study in BeaverDam, Wisconsin. These findings are consistent withtwo previous reports of relationships with these lipid-phase antioxidant nutrients.1013 They contrast withfindings of other studies which suggest protective asso-ciations with at least one lipid phase antioxidant inthe blood.1112 Inconsistencies between studies indi-cate that these associations are either weak, hard tomeasure, or are influenced by differences betweenstudy populations or study designs.

Carotenoids

One reason for finding no overall protective relation-ship of serum carotenoids in the Beaver Dam popula-tion could be that levels of carotenoids may be eitherabove or below thresholds at which an effect may oc-cur. It is known that nutrients can have differing ef-fects depending on the level of nutrients in the tissue.The extent to which this may explain differing results

between studies cannot be directly evaluated becauseof the inconsistency in the types of carotenoids mea-sured (total carotenes versus individual carotenoids).For /3-carotene, levels in the serum in the Beaver Dampopulation were compared with levels in four otherstudy populations using comparable measurementtechniques. Levels in the Beaver Dam population were10 to 50% lower (in men and women) than levelsreported in other populations.1114'24'25 Thus, levels inthis study population may be too low to detect relation-ships if a high threshold exists for an effect of increas-ing blood carotenoids or the development of lensopacities. However, the observation of odds ratios > 1in women who also had higher serum levels of manycarotenoids, would not be consistent with the notionof a high threshold.

On the contrary, data from the present studywould be more consistent with the existence of a lowthreshold. Inverse relationships were found in menrather than women who also had lower levels of most


carotenoids. Significant inverse associations for somecarotenoids in men who smoked were accompanied bylower serum levels (Table 5). Furthermore, the largestdrop in odds ratios in men occurred between the firstand second quintiles indicating the possibility of lowthreshold (data not shown). Perhaps a greater propor-tion of men than women, particularly those whosmoked in this population, had levels of carotenoidsthat were low enough to observe protective relation-ships of increasing levels. Larger observational studiesand experimental studies are needed to determinewhether thresholds for protective effects of carot-enoids exist.

A second reason for finding no protective rela-tionships could be that availability of carotenoids onlyinfluences progression to the most severe types ofopacities. Two earlier reports of protective associa-tions of serum carotenoids with lens opacities werefrom persons with more severe cataract than thoseincluded in the present study.1112 However, data fromthe present study indicate that stronger inverse associ-ations for /S-carotene are more likely to occur inyounger men who have less severe opacities than oldermen. Thus, data from the present study do not sup-port stronger relationships in older persons (andtherefore persons with more severe opacities). Rather,our data suggest the relationship of carotenoid statuswith nuclear sclerosis risk (at least in men) may begreater in the earlier stages.

Another reason for the lack of overall protectiverelationships of serum carotenoids in this and someother studies1013 may be that protective relationshipsof higher serum carotenoids exist only within certainpopulation subgroups who may be represented tovarying degrees in the samples studied. The presentstudy indicates that protective relationships betweensome carotenoids and nuclear and cortical opacitiesmight exist only in men. Furthermore, some inverserelationships with nuclear opacities were observedonly in men who smoked. A lack of statistical powerdue to small sample size may explain the lack of statis-tical significance of relationships with some carot-enoids when analyzed in subgroups. For example, weestimated that the power to detect associations withobserved odds ratios ranged from 2% (for a-carotene)to 70% (for lycopene) if analyzed in our group of180 men, based on previously described calculations.28

Therefore, while statistical power may have been ade-quate for detecting relationships of some carotenoidsin the whole group (see Methods section), it may havebeen inadequate to detect relationships in smaller sub-groups such as in men or in smokers.

This is the first report of relationships betweenlens opacities and individual levels of carotenoids inthe serum other than /J-carotene. Results indicate theassociations with lens opacities differ among individ-

ual carotenoids. We found that higher levels of lyco-pene, the most abundant carotenoid in the serum,were associated with increased risk for more severenuclear sclerosis. These results are generally consis-tent with retrospective dietary data, which indicatetrends for more severe nuclear sclerosis with higherlevels of intake of this carotenoid.29

Vitamin E

Vitamin E is the most potent lipid-phase antioxidantin the serum.30 However, we found no inverse relation-ships between level of a-tocopherol in the serum andseverity of nuclear opacities in the present study. Simi-larly, dietary levels of vitamin E were not cross-section-ally related to nuclear opacities (Table 4). Low levelsof a-tocopherol, the most active form of vitamin E,were related to higher prevalence of nuclear cataractsin the Baltimore Longitudinal Study of Aging Co-hort.11 The reason for discrepant results between thetwo studies is unclear. Proportions of each sample withlow levels of a-tocopherol in the serum appear to besimilar. The 25th percentile cutoff for levels of a-to-copherol in this population (9 mg/dl) was similar tothat in the Baltimore population (8 mg/dl). Further-more, results for the present population are similarwhen using the analytic strategy used in the Baltimorepopulation (polytomous logistic regression). Theremay be other unidentified differences between studypopulations that explain the inconsistent findings be-tween these two studies.

In contrast to a-tocopherol, levels of •y-tocopherolin the serum were inversely related to nuclear butnot cortical opacities. Gamma-tocopherol is a far lessabundant vitamin E compound than a-tocopherol inthe serum (Table 2) and may have only a small frac-tion of the ability to quench free radicals comparedwith a-tocopherol.31 The reason for different findingsfrom those for a-tocopherol could be explained bythe reciprocal absorption of these two vitamin E com-pounds. The American diet now contains two to fourtimes more y-tocopherol than a-tocopherol.32 How-ever, a-tocopherol competes more favorably for ab-sorption and transport on lipoprotein particles. Theresult is a reciprocal relationship in serum concentra-tion of these two E vitamins, a common observationin population studies.33

Direct Associations With Nutrients

In women, an unexpected increase in risk for nuclearand cortical opacities associated with higher levels ofseveral carotenoids in the serum was observed. Simi-larly, higher levels of a-tocopherol were associatedwith higher risk for cortical opacities and marginallyhigher risk for nuclear opacities in both men andwomen. Neither smoking status (Table 5) nor age in-fluenced the direction of these relationships. The as-


Baseline (1988-90)Serum

WomenMen

IntakeWomen

Men

Past (1978-80)Intake

WomenMen

0 1 2 3 4 5 6 7

OR (95% Cl)

FIGURE 1. Odds ratios for more severe nuclear sclerosisamong persons in the highest versus lowest quintiles for a-carotene in the diet or serum. Odds ratios in dietary studiesare adjusted for age (years), pack-years of smoking, andheavy drinking. Odds ratios in serum study is adjusted forage (years) and level of total cholesterol in the serum. (Asso-ciations were not influenced by adjustments for pack-yearsof smoking or heavy drinking.) The sample includes 202women and 173 men from a random sample (n = 400) ofpersons aged 50 to 86 years in the Nutritional Factors inEye Disease Study of Beaver Dam, Wisconsin, 1988 to 1990(n = 2152).

sociation of higher risk with higher serum levels ofthese nutrients could indicate that people who eatfoods or take supplements that are higher in thesenutrients are also more likely to engage in unmeas-ured behaviors that may increase risk for one or bothopacities. However, no risk factors associated with nu-clear or cortical opacities that were measured in ourstudy have been able to explain these findings.

Direct relationships with carotenoids and a-to-copherol in the serum were unexpected and could beattributable to temporal confounding. Finding similarcarotenoid and tocopherols levels in people who knewthey had cataracts and those who did not indicatesthat diet change because of knowledge of cataracts isunlikely to explain this result. Yet, for most carot-enoids and vitamin E, direct relationships with levelsin serum and severity of nuclear sclerosis are inconsis-tent with retrospective dietary studies in a larger sam-ple (n = 1929) of the Beaver Dam population.29

Such inconsistency is illustrated in Figure 1, whichdescribes associations between nuclear sclerosis andlevels of a-carotene in the diet in cross-sectional stud-ies reported here and retrospective dietary studies inpersons in the present study who provided data atboth time periods (n = 202 women and 173 men). Inmen, the inverse association with dietary a-carotenein the past time period (1978 to 1980) is consistentwith the pattern observed in this report in cross-sec-tional studies of both diet and serum levels of thisnutrient. In contrast, in women, direct relationshipsobserved in these cross-sectional studies are inconsis-tent with results of retrospective dietary studies. The

consistency between cross-sectional and retrospectivedietary studies in men and inconsistency between suchstudies in women is also, seen when comparing resultsof dietary studies in the entire cohort participating inthe Nutritional Factors in Eye Disease Study {n =2152) (Mares-Perlman, unpublished data). These pat-terns of association in cross-sectional and retrospectivestudies are generally seen for all other individual ca-rotenoids (except lycopene) and vitamin E.

These inconsistencies between results of two sepa-rate study designs suggest the possibility of temporalconfounding due to change of diet. Because of therecency of government recommendations to increasefruit and vegetable intake, a higher rate of diet changein the few years preceding the baseline (1988 to 1990)can be expected. Carotenoid estimates in the year be-fore baseline and to a greater extent carotenoid esti-mates in serum at baseline, would more likely reflectthese recent changes whereas dietary carotenoid esti-mates from 10 years before may reflect dietary habitsover a larger part of adult life. One speculation fordifferent findings in cross-sectional and retrospectivestudies is that women (but not men) who have moresevere nuclear sclerosis are more likely to have begunto eat more fruits and vegetables (which are dietarysources of carotenoids) within the past 10 years. Con-sistent with this notion, women with severe nuclearsclerosis reported a slightly greater positive change inconsumption of fruits and vegetables from past diet(1978 to 1980) to baseline diet (1988 to 1990) thandid women with less severe nuclear sclerosis (data notshown). In contrast, men, particularly those with moresevere nuclear sclerosis, generally reported a decreasein intake of fruits and vegetables at baseline, relativeto 10 years earlier. While higher intake of fruits andvegetables in women is probably unrelated to knowl-edge of having cataracts specifically, it could be relatedto having other unidentified conditions of aging thatmight be linked to nuclear sclerosis.

An alternative explanation for discrepancies be-tween cross-sectional and retrospective studies areother biases associated with the retrospective design(e.g., loss of part of cohort due to mortality). Prospec-tive longitudinal studies are needed to assess the de-gree to which this type of temporal confounding mayinfluence the cross-sectional associations in this andother studies and the gender-related differences ob-served in the present study. In general, these observa-tions serve as a reminder that confounding (or mea-surement error) due to diet change might partly ex-plain the inconsistency between cross-sectional studiesof antioxidant nutrients and lens opacities publishedto date.

Gender DifferencesDifferences in associations with nuclear sclerosis be-tween men and women could be due to several factors.


Little is known about the etiology of these opacitiesand whether pathogenic mechanisms could differ inmen and women. Differences might be explained inpart by methodologic factors such as temporal con-founding, which was discussed previously. Anotherpossible explanation is that only very low serum levels,which are more likely in men, for most carotenoidsare associated with increased risk for nuclear sclerosis.Higher ievels in serum above a certain threshold mayconfer no additional protection. One final explana-tion is that there may be a difference in susceptibilityto carotenoid modification of nuclear sclerosis be-tween men and women. For example, this could occurif environmental exposure to oxidants was higher inmen, placing greater dependency on availability ofantioxidant nutrients. Smoking is one such risk factorthat more men than women are exposed to. Inverseassociations with levels of some carotenoids were obvi-ous in men but not women who smoked.

Other Considerations

Relationships of carotenoids and tocopherols with cor-tical opacities were often similar to those observedwith nuclear opacities although they were not alwaysstatistically significant. Sufficient statistical power wasavailable to test relationships with nuclear opacitiesbut not cortical opacities in the overall sample. Never-theless, similar patterns were observed for both opacit-ies even after stratifying by the absence or presenceof the other opacity; cortical opacities were often in-versely related to carotenoid levels in men and directlyrelated to levels in women. The similarity in patternsmay indicate a similarity in some process or processesinvolved in the development of these opacities despiteobservations that biochemical and structural charac-teristics and risk factors differ between these types ofopacities.

CONCLUSION

Previously hypothesized relationships between higheravailability of lipid-phase antioxidants, vitamin E, andcarotenoids, and reduced severity of nuclear opacitieswere not supported by this cross-sectional study of nu-clear opacities at levels common in people older than50 years in the general population. The present studyraises the possibility that these relationships exist onlyin vulnerable population subgroups, which warrantsfurther investigation.

Comparison of results with retrospective dietarystudies conducted in the same population indicatethat findings of increased risk for more severe nuclearsclerosis in women could be due to temporal con-founding by diet change for many carotenoids (exceptlycopene). Longitudinal studies are needed to evalu-ate the temporal validity of these associations.

Key Words

carotenoids, tocopherols, cataract, lens, serum

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