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Can multivitamins have a clear preventive effect on chronic diseases?

December 18, 2013

Three new US studies conclude that studies evaluating potential effects of multivitamin supplementation in the prevention of cardiovascular disease, cancer and cognitive decline show insufficient evidence for benefits or harmful impacts. The researchers suggested that future studies are needed to clarify whether multivitamin supplementation may be more beneficial in persons with less optimal nutritional status or vitamin deficiencies.

A review included five large randomized controlled trials on the potential benefits and harms of multivitamin/ multimineral supplements in the primary prevention of cancer, cardiovascular disease, or all-cause mortality in healthy nourished adults, as well as 24 studies of single or paired micronutrients (1). The overall analysis of the five studies showed no significant benefits or harmful effects of multivitamin/multimineral supple- ments, which were used for up to ten years. For the single or paired micronutrients (vitamins A, C, E or D, folic acid, selenium or calcium) the analysis also showed no consistent evidence to support or refute a health effect on cardiovascular disease, cancer or all-cause mortality. While some older study results indicated a probable increased risk of lung cancer in high risk participant sub-groups (heavy smokers and asbestos workers) using large doses of beta-carotene, the new review concluded that there is adequate evidence that long-term supplementation with vitamin E has no significant harmful effect, and that there is insufficient data to conclude that calcium supplementation is harmful. The researchers commented that the review focused on randomized controlled trials, a study design used primarily to evaluate drug therapy, which might not be ideally suited to evaluating nutrients.

A randomized controlled trial evaluated potential positive effects of a supplementation with beta-carotene, vitamin C, vitamin E, a multivitamin or a placebo for up to 12 years on cognitive function (e.g., verbal me- mory) in 5947 male physicians aged 65 years or older (2). The study results showed no significant differen- ces in the change of cognitive function over the study period between the multivitamin and placebo groups. The results indicated a probable worse cognitive decline in the multivitamin group versus the placebo group. However, the researchers noted that these results must be interpreted cautiously given the small number of participants in the placebo group (372 participants) and the probably random increase in cognitive function at the first assessment for the multivitamin group. They said that future studies are needed to clarify whether multivitamin supplementation may be more beneficial in persons with less optimal nutritional status or vitamin deficiencies. This is of particular interest in an aging population because older persons are often at risk for nutritional deficiencies due to reduced micronutrient intake, altered absorption, and the metabolic requirements of vitamins.

Another randomized controlled trial evaluated the potential prevention of recurrent myocardial infarction, stroke or hospitalization for angina in 1708 patients aged 50 years or older who had previously experienced a myocardial infarction and received hereafter standard medications and a high-dose oral multivitamin/multi- mineral supplement or a placebo for an average of 31 months (3). The study results showed that multivita- min/multimineral use did not statistically significantly reduce cardiovascular events in patients compared to the placebo group. No evidence suggested harm from vitamin/mineral therapy in any category of adverse events. The researchers commented that, unfortunately, the adherence to the dosing regimen was discon- tinued by a large number of the participants due to a variety of factors, such that it was not possible to achieve any statistically meaningful or repeatable conclusion.

Experts commented the value of using a multivitamin/multimineral supplement depends on many factors: the quality of diet, health status, age, life-style factors, and genetics. Supplements can help people who are not consuming recommended amounts of nutrients to obtain the vitamins and minerals their bodies need. They are not substitutes for a good diet. They said that good nutrition needs to be part of a life plan, every day, every month, every year. However, it is not realistic to expect nutrients to act like drugs: drugs are used to treat and mitigate disease, while nutrients are needed for regular cell metabolism.

References

  1. Fortmann S. P. et al. Vitamin and Mineral Supplements in the Primary Prevention of Cardiovascular Disease and Cancer: An Updated Systematic Evidence Review for the U.S. Preventive Services Task Force. Ann Intern Med. 2013; 159:824–834.
  2. Grodstein F. et al. Long-Term Multivitamin Supplementation and Cognitive Function in Men – A Randomized Trial. Ann Intern Med. 2013; 159:806–814.
  3. Lamas G. A. et al. Oral High-Dose Multivitamins and Minerals After Myocardial Infarction – A Randomized Trial. Ann Intern Med. 2013; 159:797–804.