Supplements (vitamins, minerals, antioxidants)

The US Preventive Services Task Force evaluated the published literature in 2002 and concluded that there is not enough evidence to recommend for or against the use of:
1) vitamins A, C or E;
2) multivitamins with folic acid; 3) antioxidants for the prevention of cancer or cardiovascular disease. The Task Force also recommended against the use of beta-carotene supplements. These conclusions do not mean that vitamins are without benefit, but the evidence against major diseases is lacking.

To read the evidence published in July 2002 Annals of Internal Medicine:

Cynthia D. Morris and Susan Carson. Routine Vitamin Supplementation To Prevent Cardiovascular Disease: A Summary of the Evidence for the U.S. Preventive Services Task Force Ann Intern Med, Jul 2003; 139: 56 - 70.

U.S. Preventive Services Task Force* Routine Vitamin Supplementation To Prevent Cancer and Cardiovascular Disease: Recommendations and Rationale
Ann Intern Med, Jul 2003; 139: 51 - 55.

http://www.ahrq.gov/clinic/uspstf/uspsvita.htm

Food rather than pharmacology – that is the bottom line. 

The evidence is unequivocal that high plant food diets protect against chronic diseases. But there is much less evidence that we know the active constituents. 

In the 1995 National Nutrition Survey, 15% of men and 27% of women in Australia had taken vitamin/mineral supplements on the day prior to the survey. 

Dietary supplements may contain many times the recommended dietary intake (RDI) and an overdose from inappropriate use is possible. Furthermore, if taking purified supplements one will miss out on phytochemicals and other beneficial unidentified compounds found in food. 

Supplements of one nutrient may inhibit absorption of other nutrients in foods e.g. an iron supplement may decrease absorption of calcium and zinc from food. 

Very large doses of certain vitamins may be toxic e.g. excessive vitamin A during early pregnancy can cause fetal malformation. Taking supplements may encourage people to become ‘laid-back’ about their diet and to develop a false sense of security that they have all the nutrients they need for good health. 

People at risk of nutrient deficiencies:

Elderly persons (Ca, Zn, Mg, B6, folate), the isolated, widowers
Teenagers/young adults
Women (pregnancy, lactation, menstruation)
Smokers (vitamin C, E, b-carotene)
Alcohol abuse (vitamin B, C, Mg, Zn)
Dieters, dancers, models (who consume <1200kcal per day)
Long-term drug medication (diuretics K, Mg)
Vegetarians, vegans (vitamin B12, Fe, Ca)
Intestinal malabsorption (fat soluble vitamins)
Chronic ailments (diabetics avoiding cereals/eggs/meat lead to chromium deficiency high blood sugar levels)

Vitamin/Mineral supplements may be needed in addition to a varied diet for the following:

Calcium - vegans, the lactose intolerant and post menopausal women who find it difficult to consume 3-4 serves of dairy foods daily

Iron/Zn - vegetarians who do not consume legumes or nuts daily, pregnant women who do not eat meat/ legumes or nuts daily.

B12 - vegans (e.g. if they do not choose food products fortified with B12 like some soy milks)

Folate - women of child bearing who do not consume enough fruit, vegetables, legumes and cereals; need 400mcg/day in the first month prior to conception and for first 3 months of pregnancy to reduce risk of having a baby with neural tube defects such as spina bifida.

Vitamin C - smokers use up twice as much vitamin C for their metabolic processes compared with non-smokers

Vitamin E - people on very low-fat diets

Multivitamins (preferably at the level of the Recommended Dietary Intakes or RDI's) - people on chronic low energy diets for weight loss (<1200kcal/day) or restrictive diets due to allergies/food intolerances or recovering from serious illness/surgery.

Antioxidant supplements

Clinical trials have either found no effect, or worse, found a slightly higher incidence of disease in those randomised to get antioxidant vitamin supplements. 

There is no evidence that changing blood levels of antioxidant vitamins and phytochemicals alters mortality. They exist in their thousands and work synergistically – which may be the reason for their potency. Some work better when co-ingested in a group of antioxidants and are also better absorbed e.g. enhancement of lycopene absorption in the presence of b-carotene. When isolated from their companion compounds, some function differently (and maybe undesirably) and not as effectively. 

A major problem with all antioxidants is they can also function as pro-oxidants. When given as a supplement, it is in a dose unlikely to be achieved from even a good diet where they occur/interact with many other antioxidants in food e.g. b-carotene does not occur in foods in isolation from its hundreds of carotenoid relatives. Another area of concern about supplements is how much suppression of oxidation may be compatible with good health as 'toxic' free radicals are required for defence mechanisms. 

Epidemiological data gave us the first clues on antioxidants, with several hundred studies being published claiming those who ate foods high in various antioxidants have the lowest incidence of cancers at almost every site in the body. The first assumption was that antioxidant vitamins in protective foods were responsible for most of their advantageous effects. 

B-carotene was believed to be the active constituent in green leafy vegetables and other plant foods that protected against cancers and heart disease. So a number of trials were commenced. They had to be stopped because mortality was higher in the people taking the b-carotene supplements. 

In a study of 22,000 men taking b-carotene for 12 years, they were no better off than the men on placebo (Hennekens et al. NEJM 1996; 334: 1145-9). In another study, 18000 smokers and former smokers and the people who took b-carotene supplements had almost a 30% increased chance of developing lung cancer compared to those who took placebo, 17% increased chance of dying of any cause and 46% greater chance of dying from lung cancer compared to the placebo group. For these reasons the trial was stopped (Omenn et al. NEJM 1996; 334: 1150-5). In another study, subjects taking b-carotene supplements developed more bowel polyps. 

This does not mean the original studies showing protective effects from fruits and vegetables are wrong, but that the assumption that the benefit came from vitamins is unwarranted. The fault may lie in the interpretation of the original epidemiology. What this is saying is that it is the combination of a whole range of compounds, most of which we probably don't even know about, that are in plant foods, that is giving us the protection. When you artificially remove one of them and provide it completely out of context, it can, if anything, become a pro-oxidant. 

Vitamin E appears a bit more promising against heart disease. People who eat foods rich in vitamin E tend to have a reduced risk of heart disease, but the picture for vitamin E supplements is less clear. One large study involving 34,000 post menopausal women showed that vitamin E could be beneficial when it comes from food, but not in pills (Kushi et al. NEJM 1996; 334:1156-1162).

Supplements of vitamin E may be beneficial, especially in the elderly (Paolisso et al. AJCN 1995; 61 (4): 848-852) and for those who already have heart disease, or for those with elevated heart disease risk factors such as high cholesterol, family history or hypertension. This study reported lower insulin responses to glucose, blood fats and reduced oxidative metabolism, suggesting a greater anti-oxidant effect on free radicals. But more evidence is needed to see whether these results translate into fewer heart attacks. However, high doses of vitamin E have been associated with increased risk of mortality from some cancers, possibly fatal myocardial infarction and haemorrhagic stroke (Stephens et al. Lancet 1996; 347: 781-6). 

Also, it is not clear whether vitamin C in pills can cut the risk of cancer and it does not appear to reduce the risk of heart disease, but it may provide protection against loss of sight associated with cataracts in older people. It may turn out to have some benefit, but at levels you can quite easily get from food. 

Polyphenols, quercetin and resveratrol, in red wine are antioxidants and may explain why the French have less heart disease despite high intakes of saturated fat. Similarly, flavonoids in green tea may be partially responsible for fewer deaths from heart disease in Japan. 

A supplement called 'Juice plus' is supposedly made by juicing a variety of fruit and vegetables, drying them and
putting them in capsules. However a study has found that one capsule roughly equalled 10g of fresh fruit or vegies. 

In summary:

Many scientists believe it is the synergistic cocktail of protective compounds found in fruit, vegetables and wholegrain cereals that hit the target. This view allows for the possibility that some undiscovered substances may have even more potent antioxidant activity or that some phytochemicals may not act as antioxidants but will protect against disease in other ways.

The evidence so far suggests that benefits come from a combination of substances in foods working together. Variety is the key, so that you get different kinds of antioxidants and other potential health-enhancing compounds.

There is not enough evidence that large doses of certain nutrients or phytochemicals can improve health or decrease risk of disease where food cannot (Kushi et al., NEJM 1996; 334: 1156-62; Jha et al. Ann Intern Med 1995; 123: 860-72). 

Nor is hedging your bets by taking a range of individual supplements likely to provide the answer. 

We need more evidence about how individual supplements interact and the possibility of harm from certain combinations. 

For some people, taking a supplement may make them less inclined to make other important health-enhancing changes to their lifestyle - not smoking and avoiding excessive drinking could be more important for reducing free-radical damage to your body and improving health. 

Our best evidence is that eating more fruits, vegetables and cereals and fewer highly processed and polyunsaturated n-6 fats may offer some antioxidant protection. Claims that antioxidant supplements have a therapeutic benefit are scientifically unjustified and invitro antioxidant activity may not be relevant in vivo. Dose response data are required to evaluate pharamacologic and toxicologic effects. Their promotion as therapeutic agents is inappropriate when their efficacy is unproven and their toxicology uncertain.

See also an interesting article on antioxidant supplements in Choice Magazine (on-line) published in 2000.

For more information on antioxidants click here.

Last Updated: August 2003