[LRC Network] Fw: The Vitamin E Saga: Lessons in Patient-Oriented Evidence
Posted июль 5th, 2006 by Ibra
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From: "irina ibraghimova"
To: "irina ibraghimova"
Sent: Friday, June 30, 2006 8:48 PM
Subject: The Vitamin E Saga: Lessons in Patient-Oriented Evidence
The Vitamin E Saga: Lessons in Patient-Oriented Evidence
http://www.aafp.org/afp/20050601/editorials.html
MARK H. EBELL, M.D., M.S.
Athens, Georgia
"Physicians should consider two key factors when weighing new information
about the effectiveness of a treatment: the quality of the evidence
supporting its use and whether the evidence focuses on patient-oriented
outcomes or disease-oriented outcomes. Each of these factors is a continuum,
and each physician chooses the point at which he or she is comfortable
recommending something for patients."
"The continuum of study quality begins with case reports and case series,
progresses to observational studies (cohort or case control), and ends with
randomized controlled trials (RCTs). ...However, it is important to remember
that even large
observational studies are more subject to bias than well-designed RCTs. Such
was the case with many observational studies of hormone therapy that found
reductions-not increases-in cardiovascular mortality rates. RCTs are least
subject to bias and, although sometimes limited by their generalizability,
they are best able to prove causality."
"Human beings are complex, and positive changes in
biochemical markers do not always lead to a predictable benefit. In fact,
they can be associated with an unpredictable harm."
"The example of vitamin E, which is taken in a dosage of at least 400 IU by
one in five adults older than 55 years, illustrates this seeming
contradiction.1 Vitamin E prevents oxidation of low-density lipoproteins and
prevents platelet adhesion, which theoretically should reduce the risk of
cardiovascular disease.2,3 Observational studies 4-6 found that patients
with
coronary artery disease (CAD) had lower vitamin E levels and were less
likely to have taken vitamin E when compared with control patients. "
"The first RCT 7 of vitamin E in patients with heart disease was published
in
1996. It randomized 2,002 patients with CAD to treatment with 400 or 800 IU
of vitamin E per day or matching placebo. In the conclusion of their
abstract, the authors emphasize that vitamin E substantially reduces the
rate of nonfatal myocardial infarction, with beneficial effects apparent
after one year of treatment. A careful reading of the study, though, shows
what the authors do not emphasize: a nonsignificant increase in all-cause
mortality among treated patients (i.e., 36 deaths of 1,035 in the treatment
groups compared with 27 deaths of 967 in the control group)."
"More recently, a series of large, well-designed RCTs8-10 in patients at
high
risk for developing CAD (the kind of patients who typically take vitamin E)
showed no benefit among the patients taking vitamin E. Despite the lack of
benefit, millions of physicians continued to recommend this drug in 20 times
the recommended daily allowance to their patients. "
"The first indication that vitamin E might be harmful came from a study 11
of 423 postmenopausal women
with CAD who were randomized to 400 IU of vitamin E twice daily plus 500 mg
of vitamin C twice daily or matching placebo (the study also randomized
women to hormone therapy or placebo)."
" It found a consistent dose-response relationship between vitamin E and
all-cause
mortality, with an estimated excess risk of 39 per 10,000 persons who took
high dosages of vitamin E (i.e., at least 400 IU per day) for at least one
year (95 percent confidence interval, 3 to 74)."
"By learning to value well-designed studies over weaker evidence,
and by focusing on patient-oriented evidence instead of disease-oriented
evidence, we can be more confident that our decisions to adopt a new test or
treatment will help our patients."
REFERENCES
1. Millen AE, Dodd KW, Subar AF. Use of vitamin, mineral, nonvitamin, and
nonmineral supplements in the United States: the 1987, 1992, and 2000
National Health Interview Survey results. J Am Diet Assoc 2004;104:942-50.
2. Fuller CJ, Huet BA, Jialal I. Effects of increasing doses of
alpha-tocopherol in providing protection of low-density lipoprotein from
oxidation. Am J Cardiol 1998;81:231-3.
3. Janero DR. Therapeutic potential of vitamin E in the pathogenesis of
spontaneous atherosclerosis. Free Radic Biol Med 1991;11:129-44.
4. Cherubini A, Zuliani G, Costantini F, Pierdomenico SD, Volpato S,
Mezzetti A, et al. High vitamin E plasma levels and low low-density
lipoprotein oxidation are associated with the absence of atherosclerosis in
octogenarians. J Am Geriatr Soc 2001;49:651-4.
5. Bonithon-Kopp C, Coudray C, Berr C, Touboul PJ, Feve JM, Favier A, et al.
Combined effects of lipid peroxidation and antioxidant status on carotid
atherosclerosis in a population aged 59-71 y: the EVA Study. Etude sur le
Vieillisement Arteriel. Am J Clin Nutr 1997;65:121-7.
6. Stanner SA, Hughes J, Kelly CN, Buttriss J. A review of the
epidemiological evidence for the 'antioxidant hypothesis'. Public Health
Nutr 2004;7:407-22.
7. Stephens NG, Parsons A, Schofield PM, Kelly F, Cheeseman K, Mitchinson
MJ. Randomised controlled trial of vitamin E in patients with coronary
disease: Cambridge Heart Antioxidant Study (CHAOS). Lancet 1996;347:781-6.
8. Sacco M, Pellegrini F, Roncaglioni MC, Avanzini F, Tognoni G, Nicolucci
A. Primary prevention of cardiovascular events with low-dose aspirin and
vitamin E in type 2 diabetic patients: results of the Primary Prevention
Project (PPP) trial. Diabetes Care 2003;26:3264-72.
9. Heart Protection Study Collaborative Group. MRC/BHF Heart Protection
Study of antioxidant vitamin supplementation in 20,536 high-risk
individuals: a randomised placebo-controlled trial. Lancet 2002;360:23-33.
10. Yusuf S, Dagenais G, Pogue J, Bosch J, Sleight P. Vitamin E
supplementation and cardiovascular events in high-risk patients. The Heart
Outcomes Prevention Evaluation Study Investigators. N Engl J Med
2000;342:154-60.
11. Waters DD, Alderman EL, Hsia J, Howard BV, Cobb FR, Rogers WJ, et al.
Effects of hormone replacement therapy and antioxidant vitamin supplements
on coronary atherosclerosis in postmenopausal women: a randomized controlled
trial. JAMA 2002;288:2432-40.
12. Miller ER 3d, Pastor-Barriuso R, Dalal D, Riemersma RA, Appel LJ,
Guallar E. Meta-analysis: high-dosage vitamin E supplementation may increase
all-cause mortality. Ann Intern Med 2005;142:37-46.
13. Ebell MH, Barry HC, Slawson DC, Shaughnessy AF. Finding POEMs in the
medical literature. J Fam Pract 1999;48:350-5.
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