Nearly all adult Americans have dietary deficiencies in one or more vitamins and should be taking multivitamin supplements, a new paper has asserted (JAMA 2002;287:3116-29).
Drs Robert Fletcher and Kathleen Fairfield of the Harvard Medical School's departments of public health, ambulatory medicine, and epidemiology, reached these conclusions after reviewing the literature on vitamins, nutritional supplements, toxicities, and disease states. They recommend that all adults take one multivitamin pill daily and that elderly people take two multivitamin pills as they are more susceptible to vitamin deficiencies.
The authors searched the Medline database for articles and randomised trials involving vitamins published from 1966 to January 2002.
Nine vitamins were selected for review: folic acid, vitamins B-6 and B-12, vitamin D, vitamin E, the provitamin A carotenoids, vitamin A, vitamin C, and vitamin K. Additionally, the carotenoid lycopene was included in the review because of evidence that it might help to prevent prostate and breast cancers. Thiamine (vitamin B-1) and riboflavin (B-2) were excluded because of scant evidence of their relation to chronic disease.
Although overt vitamin deficiency syndromes such as pellagra, beri-beri and scurvy are rare in developed countries, suboptimal vitamin levels are common and contribute to the chronic diseases that plague Western society, the researchers said. The literature search disclosed that people who have alcohol dependence, are elderly, are vegans, or have with malabsorptive disorders are especially at risk of vitamin deficiency. In particular, low levels of folic acid and vitamins B-6 and B-12 are risk factors for cardiovascular disease, neural tube defects, and breast and colon cancers.
High homocysteine levels are associated with atherosclerosis, and most US adults would benefit from folic acid supplementation. People with high homocysteine levels have twice the rate of coronary heart disease as those in the general population, making hyperhomocysteinaemia as much a risk factor for coronary artery disease as smoking.
Moreover, a polymorphism in the gene for methylene tetrahydrofolate reductase, which is responsible for metabolising folic acid, affects up to 15% of the population. People with this gene variant have a greater risk of colon cancer and need higher levels of folic acid supplementation than the rest of the population. Women attempting to conceive should take additional folic acid at 400µg day to decrease the possibility of giving birth to infants with neural tube defects.
The studies reviewed failed to show any toxicity associated with folic acid supplementation. Low intake of vitamin D and calcium continue to be common and contribute to osteopenia, osteoporosis, and some cancers. Vitamin E and lycopene may decrease the risk of prostate cancer.
However, clinical trials which investigated whether vitamin E could decrease coronary heart disease in high risk patients failed to confirm the lower rate of the disease seen in those taking vitamin E supplements in observational studies such as the physicians and nurses health studies.
Similarly, studies involving vitamin A, retinols, and lung cancer failed to find a beneficial effect, and although there is interest in whether retinols can help prevent breast and bladder cancers, the evidence is weak. Vitamin A is hepatotoxic in overdose and can also cause changes in vision, pseudotumour cerebri, and craniofacial anomalies in fetuses. Vitamin C is well tolerated even in high doses, and toxicities are rare.
Contrary to popular belief, calcium oxalate stones were not increased in incidence in patients taking high dose vitamin C. In addition to its role as a procoagulant, vitamin K may also have a role in preventing bone loss, the studies suggested.
The study's authors advised against routine iron supplementation because of the high prevalence of haemochromatosis in the general population.
They said that there is no evidence to support one vitamin brand over another and that the cheapest ones are fine. Generic multivitamins can be bought in bulk at a cost of about £6.50 annually, they concluded.
Commenting on the work, Dr Fletcher said: "It's rare to find a health promoter that offers such a substantial benefit with a relatively low cost and low risk of problems, and people should jump on it."
