weight reduction in hypertension
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Weight Reduction in HypertensionTHOSE who have attempted to follow the continuing
argument about diet and blood-pressure1 will not besurprised to learn that two further careful studies haveproduced apparently contradictory results. One, fromMcMaster, was published last year;2 the other, fromSydney, is reported this week on p 1233. On thisoccasion the point at issue is whether clinically feasibleweight reduction yields a worthwhile reduction in
blood-pressure. The question is of the greatestimportance. Cardiovascular disease is the pre-ponderant cause of death in Western society. There isalso a close relation between blood-pressure and therisk of cardiovascular death. An excess risk is presenteven in the substantial proportion of the populationwhose blood-pressure lies in the "high normal" and"borderline hypertensive" range. For this reason asmall change in blood-pressure may have a large effectupon population (although not individual) health.Rose3 has calculated, for instance, that a downwardshift in blood-pressure distribution of 2-3 mm Hgwould probably have an effect upon cardiovasculardisease equal to that of treating all patients with adiastolic blood-pressure of 105 mm Hg or more. Theassumptions upon which such calculations are basedare untestable and likely to remain so, but it is a
reasonable conclusion that even small reductions in
1 Editorial Diet and hypertension Lancet 1984, ii: 671-732 Haynes RB, Harper AC, Costley SR, Johnston M, Logan AG, Flanagan PT, Sackett
DL Failure of weight reduction to reduce mildly elevated blood pressure. arandomised trial. J Hypertens 1984; 2: 535-39
3 Rose G Strategy of prevention. lessons learned from cardiovascular disease. Br Med J1981, 282: 1847-51
blood-pressure achieved in a harmless way would havegreat beneficial consequences.Dietary weight loss has much to commend it
as a possible non-pharmacological treatment of
hypertension. It is (at least from a health service pointof view) cheap; the principles of weight reduction arewidely discussed and approved if not actuallypractised; most important of all, the effect of weightloss upon cardiovascular risk factors other than
hypertension is likely to be beneficial rather than thereverse. There is also no doubt about the importantassociation between obesity and hypertension. In onelarge study, for instance, hypertension was twice asprevalent in younger overweight individuals and 50%more prevalent in older obese subjects than in normal-weight controls.4 The effect of dietary weightreduction upon hypertensive cardiovascular diseasehas not been examined: a study of sufficient statisticalpower to demonstrate a worthwhile effect needs to beso large that even the most enthusiastic have beendeterred. There have, however, been numerous studiesupon the efficacy of dietary weight loss in reducingblood-pressure. Benefit has usually been reported butin most cases the overall design has been flawed.Nevertheless, two groups, after critical review of thepublished work, have been impressed by the evidencefor benefit. Andrews et al/ who did a "meta-analysis",concluded that weight reduction had the largest effectupon blood-pressure of any non-pharmacologicaltherapy. Hove1l6 drew attention to the evidentdeficiencies in published work, such as the failure torandomise patients into control and treated groups andthe neglect of placebo effect and potential interactionswith concomitant antihypertensive therapy. Theinteractions need not be entirely pharmacological.Patients who comply with a diet are likely to complyalso with drug treatment, so their blood-pressure maybe unusually easy to control. Despite these difficultieshe concluded that the best studies demonstratedbenefit: as a crude approximation the strongest dataindicated that a weight loss of 12 kg gives a blood-pressure fall of 21/13 mm Hg and a weight loss of 3 kggives a fall of 7/4 mm Hg. Falls of this order have beenreported in both untreated obese hypertensivepatients7-9 and in patients receiving antihypertensivetherapy. 10,11
4 Stamler R. Stamler J, Reidlinger WF, Algera G, Roberts RH Weight and bloodpressure findings in hypertension screening of one million Americans JAMA1978; 240: 1607-10
5 Andrews G, MacMahon SW, Austin A, Byrne DG Hypertension comparison of drugand non-drug treatments. Br Med J 1982, 284: 1523-26
6 Hovell MF The experimental evidence for weight loss treatment of essential
hypertension a critical review Am J Publ Health 1982; 72: 359-687 Reisen E, Rachel A, Modan M, Siverberg DS, Eliahou HE, Modan B Effect of weight
loss without salt restriction on the reduction of blood pressure in overweighthypertensive patients N Engl J Med 1978, 298: 1-6
8 Tuck ML, Sowers J, Dornfeld L, Kledzik G, Maxwell M The effect of weightreduction on blood pressure, plasma renin activity and plasma aldosterone levels inother patients N Engl J Med 1981, 304: 930-33
9 Reisen E, Frohlich ED, Messerli FH Cardiovascular changes after weight reduction inobesity hypertension Ann Intern Med 1983, 98: 315-19
10 Ramsay LE, Ramsay MH, Hettiarachchi J, Davies DL, Winchester L Weightreduction in a blood pressure clinic. Br Med J 1978, ii: 244-45.
11 Tyroler HA. Heden S, Hames C Weight and hypertension In- Paul O, ed.
Epidemiology and control of hypertension Miami Stratton Intercontinental, 1977177-204
In view of the high prevalence of obesity in
hypertensive patients" the substitution of these figuresin Rose’s calculations would have enormous
implications for the prevention of cardiovasculardisease. There are, as always, caveats. Literature
surveys in contentious areas should be treated with
particular caution. There is an inevitable bias in
reporting and publishing positive results. In addition,the careful supervision and enthusiasm implicit in aspecifically designed short-term study is likely to yieldbetter results than do the same techniques employedfor long-term management in a clinic or surgery. Thismay be part of the reason for the apparent discrepancybetween the reports from McMaster and Sydney. Bothgroups used a rigorous design with randomisedallocation of patients to diet and control groups. In theAustralian study weight loss of 7-4 kg produced a fallin diastolic and systolic blood-pressures of the orderpredicted by Hovell’s calcu1ations.6 A unique featureof this study is the comparison with metoprolol, whichwas significantly less effective in reducing diastolicpressure. By contrast the McMaster workers recordeda weight reduction of 4 1 kg and no change in blood-pressure, even though the calculated power of the studywas sufficient for detection of an effect of the
magnitude predicted from Hovell’s analysis. Perhapsthe discrepancy is due to the lower initial blood-
pressures or the less frequent supervision in theCanadian study.In the absence of any direct information on the effect
of weight reduction on cardiovascular morbidity andmortality, the best that can be attempted is informed,deduction from physiology. As the Sydney workerspoint out, the changes in plasma lipids are likely to befavourable (compared with those induced by somedrugs), and there are other pointers to a beneficial effectof weight-lowering. In some physiological studies, thefall in blood-pressure with weight loss has beenassociated with a fall in cardiac output,9,12 probably dueto a reduction in vascular efferent sympathetic nerveactivity. 13,14 This may reflect the body’s normalhomoeostatic response to calorie restriction-ie, a
diminution of catecholamine-mediated metabolic
activity The blood-pressure fall induced by diet iscorrelated with a fall in circulating noradrenaline:’,"the response of noradrenaline to exercise is alsoreduced by dietary weight loss.’4 Whether such effectsare clinically beneficial is unknown but at least they areunlikely to be harmful. Reduced sympathetic nerveactivity may also help to lower blood-pressure lessdirectly. Plasma renin activity falls progressively withweight loss.8,14 Since the changes in sodium and fluid
12 Alexander JK, Peterson HL Cardiovascular effects of weight reduction. Circulation1972; 45: 310-18.
13. Jung RT, Shetty PS, Barrand M, Callingham BA, James WPT Role of catecholaminesin hypotensive response to dieting. Br Med J 1979, i: 12-13.
14 Sowers JR, Whitfield LA, Catania RA Role of sympathetic nervous system in bloodpressure maintenance in obesity. J Clin Endocrinol Metab 1982, 54: 1181-86
15. Landsberg L, Young JB. Fasting, feeding and regulation of the sympathetic nervoussystem N Engl J Med 1978, 298: 1295-301.
balance are likely to stimulate renin rather than reduceit, this effect too may well be traceable to reducedvascular efferent sympathetic activity.This explanation ascribes the blood-pressure-
lowering effect of weight reduction exclusively tocalorie restriction, but there may be more to the story:for instance, possible effects of alterations in lipidintake are attracting increasing attention.’ The earliersuggestion of Dahl’s team that the blood-pressure fallwas associated with decreased sodium intake" has notbeen confirmed by other studies.7,9,17 The discrepancybetween these and another recent observation is
probably more apparent than real. Andersson et all’treated two groups of obese hypertensives by dietaryweight reduction and restriction of dietary salt. Onegroup received salt supplements to restore salt intake tonormal while the other group did not. Only the lattergroup showed a significant fall in blood-pressure.However, the salt-supplemented group showed a fall inblood-pressure which, although not significant, lieswell within the confidence limits of the expected fallsuggested by Hovell’s analysis.6 It does seem possible,however, that salt restriction has an effect upon blood-pressure that is additive to weight loss. This
interpretation is supported by another study in whichthese two manoeuvres were used sequentially in twogroups of patients and independent effects were
observed." This is not unexpected: both the
sympathetic nervous system and the renin-angiotensinsystem protect the circulation against the blood-
pressure-lowering effects of fluid volume contraction,and if these systems are partly inhibited, potentiationof such an effect would be expected.There is sufficient evidence now to support the view
that every overweight hypertensive should be
encouraged strongly to lower weight. The benefitsseem directly related to the amount of weight lost. Theeffect upon hypertensive cardiovascular disease of
population measures to reduce weight is unmeasuredbut is likely to be substantial.
Systemic VasculitisTHE term systemic vasculitis encompasses a
heterogeneous group of disorders characterised byinflammatory destruction of blood vessel walls,occurring de novo (eg, polyarteritis nodosa) or as a
16. Dahl LK, Silver L, Christie RW Role of salt in the fall of blood pressure accompanyingreduction of obesity. N Engl J Med. 1958, 258: 1186-92
17. Gillum RF, Prineas RJ, Jeffery RW, et al. Non-pharmacological therapy for
hypertension the independent effects of weight reduction and sodium restriction inoverweight borderline hypertensive patients Am Heart J 1983, 105: 128-33
18 Andersson OK, Fagerberg B, Hedncr T. Importance of dietary salt in thehemodynamic adjustment to weight reduction in obese hypertensive menHypertension 1984, 6: 814-19.