effects of metformin or rosiglitazone on serum concentrations of homocysteine, folate, and vitamin...

Journal of Diabetes and Its Comp

Effects of metformin or rosiglitazone on serum concentrations of

homocysteine, folate, and vitamin B12 in patients with type 2

diabetes mellitus

Mustafa Sahin4, Neslihan B. Tutuncu, Derun Ertugrul, Nedret Tanaci, Nilgun D. Guvener

Department of Endocrinology and Metabolic Diseases, Baskent University Faculty of Medicine, Ankara, Turkey

Received 30 June 2005; received in revised form 16 September 2005; accepted 20 October 2005

Abstract

Objectives: Metformin is widely used in patients with type 2 diabetes but may decrease vitamin B12 levels and increase levels of

homocysteine (Hcy), a cardiovascular risk factor. Rosiglitazone, a peroxisome proliferator-activated receptor-g agonist, may reduce markers

of inflammation. We investigated whether 6 weeks’ treatment with metformin or rosiglitazone affects serum concentrations of Hcy, folate, or

vitamin B12 in subjects with newly diagnosed type 2 diabetes compared with controls. Methods: We examined 165 patients with type 2

diabetes. Fasting blood samples, a physical examination, and a complete medical history were performed at the beginning and at the end of

the treatment. All blood samples were obtained after a 12-h fast. Results: After treatment, metformin use was associated with an increase in

levels of Hcy by 2.36 Amol/l and decreases in folate and vitamin B12 concentrations by �1.04 ng/ml and �20.17 pg/ml. During rosiglitazone

treatment, Hcy levels decreased by �0.92 Amol/l; folate and vitamin B12 levels remained unchanged. Metformin and rosiglitazone

significantly decreased levels of triglyceride (TG), low-density lipoprotein (LDL), total cholesterol (total-C), HbA1c, insulin, and

homeostasis model assessment (HOMA). Metformin also significantly decreased body weight. In controls, there was no change in Hcy, folic

acid, vitamin B12, TG, LDL, total-C, HbA1c, insulin, or HOMA levels. Homocysteine change did not correlate with insulin, folate, or

vitamin B12 changes in the metformin and rosiglitazone groups. Conclusions: In patients with type 2 diabetes, metformin reduces levels

of folate and vitamin B12 and increases Hcy. Conversely, rosiglitazone decreases Hcy levels in this time period. The clinical significance of

these findings remains to be investigated.

D 2007 Elsevier Inc. All rights reserved.

Keywords: Rosiglitazone; Metformin; Homocysteine

1. Introduction

An elevated plasma homocysteine (Hcy) level has been

found to be a risk factor for cardiovascular disease

(Eikelboom, Lonn, Genest, Hankey, & Yusuf, 1999). Recent

studies have demonstrated that plasma Hcy is an important

risk factor also in patients with type 2 diabetes (Hoogeveen

et al., 2000; Stehouwer, Gall, Hougaard, Jakobs, & Parving,

1056-8727/07/$ – see front matter D 2007 Elsevier Inc. All rights reserved.

doi:10.1016/j.jdiacomp.2005.10.005

4 Corresponding author. Department of Endocrinology and Metabo-

lism, Baskent University, Bahcelievler, Ankara, Turkey. Tel.: +90 312

2126868.

E-mail address: [email protected] (M. Sahin).

1999). Plasma Hcy is elevated in patients with type 2

diabetes who have coexistent cardiovascular disease

(Munshi, Stone, Fink, & Fonseca, 1996).

Many factors have been found to be important in

determining plasma Hcy concentrations (Jacobsen, 1996).

These include plasma levels and intake of folic acid and

vitamin B12 (which regulate fasting Hcy) and of pyridoxine

(which regulates postmeal or postmethionine plasma Hcy)

(Jacobsen, 1996). Also, various drugs and hormones play

a role in determining plasma Hcy (Fonseca, Guba, & Fink,

1999). Low serum folate and vitamin B12 levels are

thus strongly associated with increased serum Hcy (Naurath

et al., 1995).

lications 21 (2007) 118–123

Table 1

Baseline characteristics of patients with diabetes before treatment with

metformin (Group 1), rosiglitazone (Group 2), or control (Group 3)

Group 1

(n=74)

Group 2

(n=55)

Group 3

(n=36) P

Sex 43 F/31 M 35 F/20 M 21 F/15 M NS

Age (years) 58.36F7.58 57.92F8.67 59.06F3.08 NS

BMI 29.10F3.32 29.63F3.40 28.49F3.4 NS

Weight (kg) 77.66F6.90 78.05F6.62 77.82F2.5 NS

Hcy (Amol/l) 11.95F3.95 13.06F3.92 11.33F1.51 NS

Folic acid

(nmol/L)

10.06F5.16 10.86F4.86 8.58F2.53 NS

Vitamin B12

(insulin pmol/L)

310.4F149.5 306.0F116.8 265.9F39.82 NS

HOMA 2.55F1.35 2.62F1.46 2.93F1.09 NS

Total-C 206.7F32.4 202.4F26.2 204.52F35.1 NS

LDL 131.8F32.4 129.1F25.2 135.39F37.4 NS

HDL 48.52F8.82 50.43F6.87 47.39F9.3 NS

TG 186.6F54.9 189.7F61.6 188.16F53.3 NS

Microalbuminuria 13.93F16.69 14.84F17.40 10.78F11.04 NS

HbA1c 6.65F1.11 6.52F0.66 6.95F1.26 NS

FPG, lipid parameters that are captured as millimoles per liter.

M. Sahin et al. / Journal of Diabetes and Its Complications 21 (2007) 118–123 119

Serum vitamin B12 levels are known to decrease dur-

ing metformin treatment (Tomkin, Hadden, Weaver, &

Montgomery, 1971), probably due tomalabsorption (Caspary

et al., 1977). Thus, Hcy levels may increase during

metformin treatment (Hoogeveen et al., 1997).

Thiazolinediones are a class of antidiabetic agents that

directly target insulin resistance (Parulkar, Pendergrass,

Granada-Ayala, Lee, & Fonseca, 2001). Several studies

have demonstrated a relationship between plasma insulin

and Hcy levels (Emoto et al., 2001; Meigs et al., 2001).

In addition, a negative correlation between high levels

of Hcy and peroxisome proliferator-activated recep-

tor (PPAR) expression has been demonstrated (Brude

et al., 1999). Troglitazone lowers plasma Hcy in insulin-

Table 2

Changes in serum total Hcy, folate, vitamin B12, HbA1c, and HOMA after 6 we

Variable Group Initially 6 weeks l

Hcy (Amol/l) Rosiglitazone 13.06F3.92 12.14F3

Metformin 11.95F3.95 14.30F3

Control 11.33F1.51 11.25F1

Vitamin B12

(pmol/l)

Rosiglitazone 306.0F116.8 317.2F1

Metformin 319.3F149.6 290.22F1

Control 265.89F39.8 262.14F4

Folic acid

(nmol/l)

Rosiglitazone 10.56F4.87 10.21F6

Metformin 10.06F5.17 9.01F4

Control 8.58F2.53 8.62F2

HOMA Rosiglitazone 2.62F1.46 2.26F1


Control 2.94F1.09 2.92F1

HbA1c Rosiglitazone 6.52F0.69 6.38F0


Control 6.95F1.26 6.95F1

resistant animals (Fonseca et al., 2002). Rosiglitazone, a

selective PPARg agonist (Einhorn, Aroda, & Henry,

2004), is currently in therapeutic use. We therefore

investigated its potential to decrease plasma Hcy levels

in diabetic patients.

In view of these considerations, we studied the effects of

metformin and rosiglitazone treatment on serum levels of

Hcy, vitamin B12, and folate in patients with newly

diagnosed type 2 diabetes.

2. Materials and methods

2.1. Patients

The study sample included 165 patients (99 women and

66 men; aged 36–82 years) with newly diagnosed type 2

diabetes mellitus. The participants were identified at the

outpatient diabetes clinic in the Department of Endocrinol-

ogy and Metabolic Diseases at Baskent University Hospital

in Ankara, Turkey. Diabetes mellitus was diagnosed using

the World Health Organization definition for the oral

glucose tolerance test (Alberti & Zimmet, 1998). To avoid

confounding factors known to affect plasma markers of

endothelial function, coagulation, and/or inflammation, we

applied the following exclusion criteria to all subjects:

smoking any amount of cigarettes during the previous

6 months, cardiac arrhythmia, congestive heart failure,

recent stroke, chronic renal disease, microalbuminuria

(expressed as albumin to creatinine ratio N300 Ag/mg),

severe dyslipidemia (TGs N600 mg/dl [6.74 mmol/l] or

cholesterol N300 mg/dl [7.89 mmol/l]), any use of a

medicine that might affect Hcy levels, any severe chronic

disease, or any acute or chronic inflammatory illness. In

addition, subjects were excluded from the study if they

eks of treatment with either metformin or rosiglitazone

ater

P value

for difference

Mean

difference 95% CI

.60 .01 �0.92 �0.4 to �1.44

.38 .000 2.36 2.93–1.78

.65 .609

40.5 .233 11.18 29.7–7.4

40.5 .119 �20.2 �5.3 to �45.74.4 .631

.11 .504 – –

.53 .001 �1.04 �0.42 to �1.67

.34 .287

.26 .000 �0.36 �0.21 to �0.50

.92 .000 �0.49 �0.27 to �0.42

.03 .693

.66 .002 �0.14 �0.21 to �0.50

.93 .004 �0.31 �0.10 to �0.52

.25 .824

Table 3

Difference between delta changes (D) of Hcy, folic acid, and vitamin B12

levels in metformin or rosiglitazone groups

Variable Group Delta (D)

P value

(two-tailed)

difference

between

D of groups

DHcy (Amol/l) Rosiglitazone �5.70F16.8 .005

Metformin 24.37F23.1

DFolic acid (nmol/l) Rosiglitazone �3.02F27.8 .372

Metformin �7.02F27.2

DVitamin B12 (pmol/l) Rosiglitazone 3.65F20.6 .539

Metformin �1.57F48.0

M. Sahin et al. / Journal of Diabetes and Its Complications 21 (2007) 118–123120

exhibited any contraindication for the use of metformin.

The hospital ethics committee approved the protocol, and

all participants gave written informed consent.

From the beginning of the study, all subjects were given

advice for a healthy, moderately calorie-restricted diet and

an active lifestyle. After 4 weeks, all patients were randomly

assigned to receive metformin or rosiglitazone in addition to

following the recommended lifestyle modifications. All

patients receiving metformin (Group 1) successfully

increased the dosage from one to two tablets of 850 mg

per day over the 6-week study period. The first tablet was

taken at bedtime and the second at breakfast. Patients

receiving rosiglitazone (Group 2) took 4 mg at breakfast per

day. Thirty-six patients received only lifestyle modification

for 6 weeks (Group 3).

At the beginning and at the end of the 6-week

short-term treatment phase, fasting blood samples were

drawn, a physical examination was conducted, and a

complete medical history was taken. All blood samples

for the measurements were obtained after a 12-h fast

(at 0800 h) and a 24-h abstinence from alcohol and vigo-

rous exercise.

Table 4

Changes in serum FPG, fasting insulin, total-C, LDL, HDL, and TG after 6 wee

Variable Group Before treatment

Weight (kg) 1 77.65F6.9

2 78.06F6.6

BMI 1 29.10F3.32

2 29.63F3.4

FPG (mmol/L) 1 125.66F32.14

2 123.21F23.06

Insulin (pmol/l) 1 8.07F3.1

2 8.57F4.5

Total-C 1 206.7F32.37

2 202.4F26.21

HDL-C 1 48.52F8.82

2 49.74F6.81

LDL-C 1 131.79F32.44

2 129.12F25.20

TG 1 186.62F54.9

2 189.68F61.6

FPG, lipid parameters.

2.2. Laboratory investigation

Lipid profile [total cholesterol (total-C), high-density

lipoprotein cholesterol (HDL-C), low-density lipoprotein

cholesterol (LDL-C), triglyceride (TG), Hcy concentrations,

vitamin B12 levels, folic acid levels, and basal insulin levels]

was measured in serum. Levels of plasma fasting glucose,

total-C, HDL-C, and TG were determined by the calori-

metric method using a Cobas Mira Plus autoanalyzer

(Roche Diagnostics, Mannheim, Germany). Low-density

lipoprotein cholesterol levels were calculated by the

Friedwald formula.

Plasma insulin, Hcy, folic acid, and vitamin B12 concen-

trations were measured with the chemiluminescent method

using an Immulite 2000 immunoassay analyser (DPC, Los

Angeles, USA). Insulin sensitivity was calculated using

the homeostasis model assessment (HOMA) [formula:

fasting glucose (mmol/l)�fasting insulin (mU/ml)/22.5]

(Matthews et al., 1985).

Microalbuminuria and HbA1c were measured with

immunoturbidimetric method using a PP modular auto-

analyzer (Roche Diagnostics).

2.3. Statistical analyses

Statistical analyses were performed using SPSS software

(Statistical Package for the Social Sciences, version 10,

SSPS, Chicago, IL, USA). Data are expressed as meansFS.D. An analysis of variance test was used to analyze

differences between groups. Differences between the

two groups were analyzed using the independent Student’s

t test. The paired-samples t test was used to analyze changes

in variables before and after treatment in groups overall.

The changes in plasma Hcy were expressed as a change

from the referral value in percentages. The correlation

was tested by the Pearson correlation test. In all results

ks of treatment with either metformin or rosiglitazone

After treatment Mean difference (95% CI) P

77.17F7.03 0.48 (0.34–0.63) .000

78.17F6.54 .456

28.91F3.34 0.18 (0.13–0.24) .000

29.67F3.37 .415

115.40F21.95 10.26 (3.48–17.03) .004

116.63F21.72 6.58 (2.85–10.30) .001

7.17F2.9 0.90 (0.30–1.51) .004

7.8F4.14 0.78 (0.42–1.15) .000

192.4F28.19 14.32 (8.14–20.5) .000

194.1F27.9 8.35 (3.18–13.5) .002

48.51F8.55 .711

50.43F6.87 .268

121.75F27.77 10.04 (6.47–13.61) .000

120.29F21.55 8.83 (4.78–12.9) .000

172.05F53.01 14.57 (5.9–23.23) .001

173.76F55.74 15.90 (8.74–23.07) .000

Table 5

Correlation between Dhomocystine and in metformin or rosiglitazone


obtained, values for P less than .05 were considered statisti-

cally significant.
groups
Variable DFolic acid

DVitamin

B12 DInsulin DHOMA

Basal

HOMA

D Hcy

Rosiglitazone NS NS NS NS NS

Metformin NS NS NS P=.008

(r=�.336)P=.03

(r=.340)

3. Results

Table 1 shows the baseline characteristics of patients at

the start of the short-term active treatment phase. Patients

were randomized to receive either metformin or rosiglita-

zone. All baseline characteristics were comparable between

the three groups.

3.1. Hcy, folate, and vitamin B12

There were no significant changes in Hcy, vitamin B12,

or folic acid concentrations in patients in the control group

after 6 weeks.

During rosiglitazone treatment, Hcy decreased by

�0.92 Amol/l (95% CI, �0.4 to �1.44; P=.01). Folate

and vitamin B12 did not change significantly (Table 2).

Duringmetformin treatment,Hcy increased by 2.36Amol/l

[95% CI, 2.93–1.78 (24.37%); P=.000], folate decreased

by �1.04 ng/ml (95% CI, �0.42 to �1.67; P=.001), andvitamin B12 did not change significantly (Table 2).

There was a significant difference in Hcy changes but not

in folate or vitamin B12 between the metformin and

rosiglitazone groups (Table 3).

3.2. Body weight, glucose, and lipid

metabolism assessments

There were no significant changes in fasting plasma

glucose, HbA1c, insulin, HOMA index, total-C levels,

LDL-C, HDL-C, and TG levels in the control group after

6 weeks.

Fasting plasma glucose, HbA1c, insulin, HOMA index,

total-C levels, LDL-C, and TG levels decreased signifi-

Fig. 1. Correlation between Hcy change and HOMA change during

metformin treatment (Hcy, picomoles per liter).

cantly in both treatment groups. High-density lipoprotein

cholesterol levels did not change significantly in both

treatment groups. Weight and body mass index (BMI)

decreased significantly in the metformin group but did not

change in the rosiglitazone group (Table 4).

No significant correlation was found between Hcy levels

and age, BMI, insulin, HOMA, HbA1c, blood glucose level,

and vitamin B12 levels. There was a correlation between

microalbuminuria and Hcy levels (r=.303, P=.001). There

was a negative correlation between folic acid and Hcy levels

(r=�.227, P=.016).Also, there were no correlations between Hcy change and

folate, vitamin B12 or insulin, HOMA, blood glucose,

HbA1c, weight, and BMI changes during therapy. In the

metformin group, there was a correlation between Hcy

change and HOMA change (r=�.306 P=.008) (Fig. 1),

basal insulin level, and basal HOMA (r=.357, P=.002;

r=.340, P=.03). Patients with HOMA values greater than

2.2 had significantly higher changes in Hcy during

metformin treatment. In the rosiglitazone group, there was

a correlation between Hcy change and basal fasting glucose

(r=.270, P=.046) (Table 5).

4. Discussion

This is the first study to report on the effects of 6 weeks’

treatment (short term) with metformin on serum concen-

trations of Hcy, folate, and vitamin B12. We found that

6 weeks of metformin treatment in patients with type 2

diabetes was associated with a significant increase in serum

Hcy of about 2.36 Amol/l (24.37%) and with decreases in

serum folate by 1.04 ng/ml (7.02%). Vitamin B12 levels

decreased by 20.2 pg/ml, which was not statistically

significant. But metformin treatment may be associated

with a decrease in serum vitamin B12 earlier than expected.

Previous studies have reported that metformin treat-

ment is associated with decreases in serum vitamin B12

(Callaghan, Hadden, & Tomkin, 1980; Caspary et al., 1977).

Metformin is thought to induce malabsorption of vitamin

B12 in durations longer than the one used in our study

(Bauman, Shaw, Jayatilleke, Spungen, & Herbert, 2000;

Tomkin et al., 1971).

How metformin affects folate status is not known,

but findings similar to ours have been reported (Wulffele

et al., 2003).

M. Sahin et al. / Journal of Diabetes and Its Complications 21 (2007) 118–123122

The metformin-associated increase in serum Hcy in our

study is not correlated with folate or vitamin B12 during

treatment. Increasing insulin sensitivity during metformin

treatment may be the cause of early unexpected Hcy

increase. Increasing global insulin sensitivity by met-

formin may increase serum Hcy levels. Fonseca, Fink,

and Kern (2003) reported that insulin sensitivity corre-

lated with plasma Hcy levels also in nondiabetic patients.

The clinical significance of such an increase in Hcy is

not yet clear. A recent meta-analysis estimated that in

nondiabetic individuals, a persistent increase in serum

Hcy may be associated with increases in the risk of

coronary heart disease and stroke (Homocysteine Studies

Collaboration, 2002).

The effects of treatment with metformin on vitamin

status and Hcy concentrations may begin earlier than

expected, as in our study, and this is an issue that

merits further investigation. Our data raise the possibility

that these favorable effects of metformin may be even

more pronounced if decreases in folate and vitamin B12

are avoided.

This is the first study to assess the effects of PPARg

activation with rosiglitazone on serum concentrations of

Hcy, folate, and vitamin B12 in patients with newly

diagnosed type 2 diabetes. Our study showed that 6 weeks

of rosiglitazone treatment significantly reduced Hcy levels

(~5.7%). Kilicdag et al. (2005) have reported in PCOS

patients that 3 months of rosiglitazone therapy resulted in a

significant increase in plasma Hcy concentrations. The

study of Kilicdag et al. was in PCOS patients; thus, the

study population may change the results. Also, our

study period was shorter than the one used in the study

of Kilicdag et al., and therefore, the full glucose metabolic

effect may not have been reached in our study. In addition,

a recently published animal experiment showed a lowered

Hcy level when using rosiglitazone treatment (Murthy

et al., 2005).

How rosiglitazone affects Hcy metabolism is not known.

Insulin-sensitizing PPARg agonists probably reverse the

insulin-resistant proinflammatory state toward normality;

thus, it is possible that the anti-inflammatory and insulin-

sensitizing effects are related. However, in our study, there

was no correlation between Hcy and insulin change. A study

by Haffner et al. (2002) previously demonstrated a reduction

in plasma C-reactive protein concentrations after a longer

period of rosiglitazone. Thiazolidinediones have been

shown to have many effects independent of their glucose-

lowering effect (Parulkar et al., 2001). The Hcy-lowering

effects of rosiglitazone may also be mediated by changes in

metabolism in Hcy (Fonseca et al., 2002). Further research

is needed to confirm this relationship and to elucidate

its mechanism.

These observations may have implications for athero-

genesis in patients treated with rosiglitazone and possibly

other thiazolidinediones. The clinical consequences of these

changes remain unclear and merit further study.

References

Alberti, K. G., & Zimmet, P. Z. (1998). Definition, diagnosis and

classification of diabetes mellitus and its complications. Part 1:

Diagnosis and classification of diabetes mellitus provisional report of

a WHO consultation. Diabetic Medicine, 15, 539–553.

Bauman, W. A., Shaw, S., Jayatilleke, E., Spungen, A. M., & Herbert, V.

(2000). Increased intake of calcium reverses vitamin B12 malabsorption

induced by metformin. Diabetes Care, 23, 1227–1231.

Brude, I. R., Finstad, H. S., Seljeflot, I., Drevon, C. A., Solvoll, K.,

Sandstad, B., Hjermann, I., Arnesen, H., & Nenseter, M. S. (1999).

Plasma homocysteine concentration related to diet, endothelial

function and mononuclear cell gene expression among male hyper-

lipidaemic smokers. European Journal of Clinical Investigation, 29,

100–108.

Callaghan, T., Hadden, D., & Tomkin, G. (1980). Megaloblastic anaemia

due to vitamin B12 malabsorption associated with long-term metformin

treatment. British Medical Journal, 280, 1214–1215.

Caspary, W., Zavada, I., Reimold, W., Deuticke, U., Emrich, D., & Willms,

B. (1977). Alteration of bile acid metabolism and vitamin-B12—

absorption in diabetics on biguanides. Diabetologia, 13, 187–193.

Eikelboom, J. W., Lonn, E., Genest, J., Jr., Hankey, G., & Yusuf, S.

(1999). Homocyst(e)ine and cardiovascular disease: A critical review

of the epidemiologic evidence. Annals of Internal Medicine, 131,

363–375.

Einhorn, D., Aroda, V. R., & Henry, R. R. (2004). Glitazones and the

management of insulin resistance: What they do and how might they be

used. Endocrinology and Metabolism Clinics of North America, 33 (3),

595–616.

Emoto, M., Kanda, H., Shoji, T., Kawagishi, T., Komatsu, M., Mori, K.,

Tahara, H., Ishimura, E., Inaba, M., Okuno, Y., & Nishizawa, Y. (2001).

Impact of insulin resistance and nephropathy on homocysteine in type 2

diabetes. Diabetes Care, 24, 533–538.

Fonseca, V., Guba, S. C., & Fink, L. M. (1999). Hyperhomocysteinemia

and the endocrine system: Implications for atherosclerosis and

thrombosis. Endocrine Reviews, 20, 738–759.

Fonseca, V., Keebler, M., Dicker-Brown, A., Desouza, C., Poirier, L. A.,

Murthy, S. N., & McNamara, D. B. (2002). The effect of troglitazone on

plasma homocysteine, hepatic and red blood cell S-adenosyl methio-

nine, and S-adenosyl homocysteine and enzymes in homocysteine

metabolism in Zucker rats. Metabolism, 51 (6), 783–786.

Fonseca, V. A., Fink, L. M., & Kern, P. A. (2003). Insulin sensitivity and

plasma homocysteine concentrations in non-diabetic obese and normal

weight subjects. Atherosclerosis, 167 (1), 105–109.

Haffner, S. M., Greenberg, A. S., Weston, W. M., Chen, H., Williams, K., &

Freed, M. I. (2002). Effect of rosiglitazone treatment on nontraditional

markers of cardiovascular disease in patients with type 2 diabetes

mellitus. Circulation, 106, 679–684.

Homocysteine Studies Collaboration. (2002). Homocysteine and risk of

ischemic heart disease and stroke: A meta-analysis. Journal of the

American Medical Association, 288, 2015–2022.

Hoogeveen, E. K., Kostense, P. J., Jakobs, C., Bouter, L. M., Heine, R. J., &

Stehouwer, C. D. (1997). Does metformin increase the serum total

homocysteine level in non-insulin-dependent diabetes mellitus? Journal

of Internal Medicine, 242, 389–394.

Hoogeveen, E. K., Kostense, P. J., Jakobs, C., Dekker, J. M., Nijpels, G.,

Heine, R. J., Bouter, L. M., & Stehouwer, C. D. (2000). Hyper-

homocysteinemia increases risk of death, especially in type 2 diabetes:

5-year follow-up of the Hoorn Study. Circulation, 101, 1506–1511.

Jacobsen, D. W. (1996). Determinants of hyperhomocysteinemia: A matter

of nature and nurture. American Journal of Clinical Nutrition, 64,

641–642.

Kilicdag, E. B., Bagis, T., Zeyneloglu, H. B., Tarim, E., Aslan, E.,

Haydardedeoglu, B., & Erkanli, S. (2005). Homocysteine levels in

women with polycystic ovary syndrome treated with metformin versus

rosiglitazone: A randomized study. Human Reproduction, 20 (4),

849–894.


Matthews, D. R., Hosker, J. P., Rudenski, A. S., Naylor, B. A., Treacher, D.

F., & Turner, R. C. (1985). Homeostasis model assessment: Insulin

resistance and h cell function from fasting plasma glucose and insulin

concentrations in man. Diabetologia, 28, 412–419.

Meigs, J. B., Jacques, P. F., Selhub, J., Singer, D. E., Nathan, D. M., Rifai,

N., D’Agostino, R. B., Sr., & Wilson, P. W. (2001). Framingham

Offspring Study: Fasting plasma homocysteine levels in the insulin

resistance syndrome: The Framingham offspring study. Diabetes Care,

24, 1403–1410.

Munshi, M. N., Stone, A., Fink, L., & Fonseca, V. (1996). Hyper-

homocysteinemia following a methionine load in patients with

non-insulin-dependent diabetes mellitus and macrovascular disease.

Metabolism, 45, 133–135.

Murthy, S. N., Obregon, D. F., Chattergoon, N. N., Fonseca, N. A., Mondal,

D., Dunne, J. B., Diez, J. G., Jeter, J. R., Jr., Kadowitz, P. J., Agrawal,

K. C., McNamara, D. B., & Fonseca, V. A. (2005). Rosiglitazone

reduces serum homocysteine levels, smooth muscle proliferation, and

intimal hyperplasia in Sprague–Dawley rats fed a high methionine diet.

Metabolism, 54 (5), 645–652.

Naurath, H. J., Joosten, E., Riezler, R., Stabler, S. P., Allen, R. H., &

Lindenbaum, J. (1995). Effects of vitamin B12, folate, and vitamin B6

supplements in elderly people with normal serum vitamin concen-

trations. Lancet, 346, 85–89.

Parulkar, A. A., Pendergrass, M. L., Granada-Ayala, R., Lee, T. R., &

Fonseca, V. A. (2001). Nonhypoglycemic effects of thiazolidinediones.

Annals of Internal Medicine, 134, 61–71.

Stehouwer, C. D., Gall, M. A., Hougaard, P., Jakobs, C., & Parving, H. H.

(1999). Plasma homocysteine concentration predicts mortality in non-

insulin-dependent diabetic patients with and without albuminuria.

Kidney International, 55, 308–314.

Tomkin, G., Hadden, D., Weaver, J., & Montgomery, D. (1971). Vitamin-

B12 status of patients on long-term metformin therapy. British Medical

Journal, 2, 685–687.

Wulffele, M. G., Kooy, A., Lehert, P., Bets, D., Ogterop, J. C., Borger van der

Burg, B., Donker, A. J., & Stehouwer, C. D. (2003). Effects of short-

term treatment with metformin on serum concentrations of homocys-

teine, folate and vitamin B12 in type 2 diabetes mellitus: A randomized,

control-controlled trial. Journal of Internal Medicine, 254 (5), 455–463.

effects of metformin or rosiglitazone on serum concentrations of homocysteine, folate, and vitamin...

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