Do multivitamins and mineral supplements prevent chronic diseases?

Do multivitamins and mineral supplements really prevent chronic diseases, and if so, how efficacious are they, and are they safe for this purpose? A recent review of published literature attempted to answer these questions1. The authors also wanted to know how the efficacy and safety of certain single nutrient supplements likely to be included in multivitamin/mineral supplements, in the primary prevention of chronic disease in the general population of adults and children. The researchers found that few trials in the US have addressed these issues, and that a trial on inadequately nourished Chinese indicated that combined Beta-carotene, vitamin E, and selenium supplementation reduced gastric cancer rate and mortality, and overall cancer mortality.

Combined vitamin C, vitamin E, Beta-carotene, selenium, and zinc supplementation reduced cancer risk in men but not in women in a French trial. The trials did not show that supplementation had any benefits of heart diseases, or on preventing cataract, although other trials did show that zinc/antioxidants helped prevent advanced age-related macular degeneration in individuals prone to the condition.The authors noted that beta-carotene or vitamin E had no benefits for preventing cancer, cardiovascular disease, cataract, and age-related macular degeneration in all but a few cases and that beta-carotene supplementation actually increased lung cancer risk in smokers and those exposed to asbestos.

They also found that folic acid alone or in combination with vitamin B12 and/or vitamin B6 did not improve cognitive function, that selenium may be useful to prevent cancer but not heart disease, and calcium to prevent bone mineral density loss in postmenopausal women, hence helps lower vertebral but not, non-vertebral fractures rates.Dose-dependent vitamin D with/without calcium helps retain bone mineral density and prevent hip fracture, non-vertebral fracture and falls. They did not find any consistent pattern of increased adverse effects of multivitamin/mineral supplements, although beta-carotene could make the skin turn yellow.

The researchers concluded that the use of multivitamin/mineral supplement might prevent cancer in persons in poor or suboptimal nutritional state, advanced age-related macular degeneration in high-risk persons, but not cardiovascular disease or cataract.The paucity of research on the safety of multivitamin/mineral supplements precluded firm conclusions by the researchers on the matter. The issue of benefits of multivitamin/mineral supplements on cardiovascular diseases, that is, diseases of the heart and blood vessels has been contentious for sometime now. For example, general population studies have suggested a link between high homocysteine levels and cardiovascular diseases, deaths from these diseases2, 3.

Homocysteine (HCY) levels increase in chronic kidney disease and as kidney function fails, cardiovascular risk rises with some studies linking this risk with increased homocysteine levels, and others showing that adjusting for kidney function, eliminates the link2.Research evidence shows that factors such as folate and B-vitamin deficiency, pre-existing atherosclerotic disease, diabetes and various drugs could increase homocysteine (HCY) levels and that folate, vitamin B6, and vitamin B12 could reduce homocysteine levels3.

Thus, should we routinely screen for, and treat high homocysteine levels? Some studies on patients with kidney failure did not demonstrate any cardiovascular benefit from homocysteine-lowering vitamins2. Indeed, that the use of folate and vitamins B6 and B12 to lower HCY levels significantly decreases cardiovascular risk remains controversial hence the need for more treatment trials for a definitive answer to this question.

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