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Antioxidant vitamins - pills
fail to score over food
Epidemiological observations suggest that risk of
cardiovascular diseases and cancer is lower among people
who maintain a high dietary intake of whole grains,
fruits and vegetables. A commonly accepted explanation
has been that antioxidant vitamins present in these
foodstuffs prevent atherogenesis and carcinogenesis by
restricting oxidative damage to cells and cellular
macromolecules. These theories have been supported by
experiments in laboratory animals. As a result of these
observations, the belief has been mooted that large doses
of antioxidant vitamins would do even better and many
millions of dollars are spent annually on synthetic
beta-carotene, vitamin A and vitamin E formulations. Drug
companies encourage this belief - it is open secret that
vitamins stimulate their growth. Unfortunately, the
conclusions from some recent large-scale studies do not
support the hype.
The Alpha-tocoferol Beta-carotene Cancer Prevention Study
[ATBC] was conducted among 29,133 male smokers - they
were given daily supplementation of 20 mg of
beta-carotene and 50 mg of alpha-tocoferol for 5 - 8
years. The intervention revealed no reduction in the
incidence of lung cancer; there were in fact 876 new
cases. The Physicians’ Health Study on 22,071 male
physicians (50% of whom were past smokers and another 11%
current smokers) with alternate day dosing of 50 mg of
beta-carotene, revealed neither benefit nor harm in terms
of the incidence of malignant neoplasms, cardiovascular
disease and death from all causes, after 12 years. The
Beta-carotene and Retinol Efficacy Trial [CARET], which
provided daily supplementation of a combination of 30 mg
of beta-carotene and 25000 IU of retinol (vitamin A) to
18,314 smokers, former smokers or workers exposed to
asbestos, suggested that the combination had no benefit.
Furthermore, the combination may have had an adverse
effect on the incidence of lung cancer, death from this
cause, cardiovascular disease and death from any cause,
among smokers and workers exposed to asbestos. A nested
case-control study using participants enrolled in the
Multiple Risk Factor Intervention Trial [MRFIT] analyzed
734 serum samples (obtained at baseline and frozen for
approximately 20 years) for several antioxidants -
carotenoids, retinol, and alpha-, gamma- and total
tocopherol. This analysis of antioxidant concentrations
by quartiles indicated no significant association of
antioxidant levels with the risk of coronary heart
disease (CHD) death or nonfatal myocardial infarction.
Finally, a very large-scale trial, on 34,486
postmenopausal women without pre-existing cardiovascular
disease, revealed that dietary vitamin E intake is
inversely proportional to the risk of death from CHD and
that such women can lower risk without any vitamin
supplements. The intake of retinol and ascorbic acid were
however not associated with reduced risk of CHD-related
death.
Thus, randomized clinical trials remain inconclusive with
regard to the role of vitamin E in cancer prevention and
cardiovascular protection. The large trials of
beta-carotene in primary prevention show no effect and on
the contrary a potential for harm. Overall, the routine
use of antioxidant vitamins should not be instituted and
should await the results of further ongoing clinical
trials such as the SU.VI.MAX study. Smokers should also
avoid using high-dose dietary beta-carotene or vitamin E
supplements. In the final analysis, it is yet to be
proven that antioxidant vitamins, taken as
pharmacological supplements, provide the same level of
protection as diet that is rich in whole grains, fruits
and vegetables. On the contrary they may do harm.
Therefore the wiser course would be to stick to such a
diet and complement it with healthy lifestyle
modifications such as giving up smoking and taking more
exercise.
References
- Beta-carotene,
vitamin A and E may not prevent cancer or
cardiovascular diseases. WHO Drug Information
1997; 11(1): 10-1.
- Evans RW, Shaten BJ,
Day BW, Kuller LH. Prospective association
between lipid soluble antioxidants and coronary
heart disease in men. The Multiple Risk Factor
Intervention Trial. Am J Epidemiol 1998, 147(2):
180-6.
- Lonn EM, Yusuf S. Is
there a role for antioxidant vitamins in the
prevention of cardiovascular diseases? An update
on epidemiological and clinical trials data. Can
J Cardiol 1997; 13(10): 957-65.
- Omenn GS.
Chemoprevention of lung cancer: the rise and
demise of beta-carotene. Annu Rev Public Health
1998; 19: 73-99.
- Hercberg S, Galan P,
Preziosi P, et al. Background and rationale
behind the SUpplementation en VItamines et
Mineraux AntioXydants (SU.VI.MAX) Study, a
prevention trial using nutritional doses of a
combination of antioxidant vitamins and minerals
to reduce cardiovascular diseases and cancers.
Int J Vitam Nutr Res 1998; 68(1): 3-20.
- Handelman GJ.
High-dose vitamin supplements for cigarette
smokers: caution is indicated. Nutr Rev 1997;
55(10): 369-70.
- Ward JA. Should
antioxidant vitamins be routinely recommended for
older people? Drugs Aging 1998; 12(3): 169-75.
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