Vitamins and dietary supplements constitute a multi-billion dollar industry worldwide, which happens to play an important role in the health and healthcare of many adults. Although effectiveness of these supplements in preventing illness is questionable, as well as not being supported by practice guidelines, they are still widely used by older adults.
The US Preventive Services Task Force (USPSTF) states there is insufficient evidence to recommend for or against the use of vitamins A, C, E, or multivitamins with folic acid or antioxidants. Specifically, the USPSTF is concerned regarding the balance of benefits vs. harms of these supplements.
The American Medical Association recommends supplements for seniors who have generalized decreased food intake, while the American Dietetic Association advises low-dose multivitamin and mineral supplements depending on individualized dietary assessment. The American Heart Association emphasizes healthy eating patterns rather than supplementation with specific nutrients.
Recommendations against the routine use of supplements are grounded in good clinical evidence. A review of 77 randomized controlled trials with 232,550 participants founds no evidence to recommend antioxidant supplementation for primary or secondary prevention of mortality. Moreover, there exists the possibility of harm with the use of some supplements. As an example, the Alpha-Tocopherol Beta-Carotene Cancer Prevention Trial demonstrated that beta-carotene supplements increased the risk of lung cancer among male smokers.
41,836 women between the ages of 55 and 69 years were enrolled in a study in 1986, with the main outcome being the relationship between supplement use and all-cause mortality. The results were adjusted to account for the following factors: age, energy intake, educational level, place of residence, smoking status, body mass index (BMI), waist-to-hip ratio, physical activity, diet composition, alcohol consumption, estrogen therapy, and the presence of diabetes mellitus and hypertension. Serum lipids or blood pressure where not measured as part of the study.
In the study participants, the use of dietary supplements were found to have increased with time; 62.7% of women reported use of at least 1 supplement in 1986, and this figure rose to 85.1% by 2004. The most commonly used supplements were calcium, multivitamins, vitamin C, and vitamin E.
Generally, women who used supplements were found to have better health characteristics compared with nonusers. They had higher educational status, lower BMI and waist-to-hip ratio, and lower rates of diabetes and hypertension compared with nonusers, and they were also less likely to smoke and had a healthier dietary profile. Supplement users were also more likely to use estrogen therapy compared with nonusers.
In total, there were 15,594 deaths (40.2% of the study) during a mean follow-up period of 19 years. In fully adjusted models, the use of multiple supplements was associated with a higher risk of mortality, including multivitamins, vitamin B6, folic acid, iron, magnesium, zinc, and copper. The use of vitamin A, beta-carotene, and selenium were associated with non-significant trends towards a higher risk of mortality; and the use of vitamins C, D, and E had nearly no effect on mortality. In contrast, taking calcium supplements significantly reduced the risk of mortality.
A further analysis using shorter follow-up intervals also confirmed the finds of higher risks of mortality with the use of iron. Moreover, there was evidence of a positive dose-response relationship between iron supplements and the risk of mortality. No dose-response effect was found for vitamins A, C, D, and E as well as the minerals selenium and zinc.
The higher risk of mortality associated with the use of iron supplements was a most interesting finding of this study. While higher levels of serum iron and transferrin saturation have been associated with a lower risk of mortality, another study found that men with a serum ferritin level of 200 mcg/l or more experienced more than a twofold increase in the risk of myocardial infarction. Both increase serum iron levels and higher transferrin saturation have been associated with an increased risk of death due to cancer.
In this study, women with existing anemia due to any number of chronic serious medical conditions, such as cancer or chronic kidney disease, could have been directed to take iron supplements by their physician, and these illnesses might thus account for their higher rate of mortality. Either way, it appears that the role of iron among adults without iron deficiency anemia is controversial, and there is little data from clinical trials to suggest a benefit to the routine use of iron supplementation among adults.
An additional interesting finding in the current study is the effect of calcium, but not vitamin D, supplements in reducing the risk of mortality. This is another controversial area since calcium supplements have been previously implicated in promoting a higher risk of myocardial infarction among women. This is while, in the Women’s Health Initiative trial, the use of calcium plus vitamin D reduced the risk of some types of cancer without an overall effect on the risk of mortality.
The finding from the current study offer several lessons to physicians, on the whole. Physicians need to pay close attention to nonprescription therapies used by patients; these treatments are routinely omitted from the history of many patients. Physicians should be a trusted resource for patients interested in dietary supplements, aiding in setting the balance between self-treatment practices that might be effective against those that appear harmful or excessive.
The overall findings of the study could be summarized as follows:
- Nearly half of older adults routinely use dietary supplements, with higher rates of use among women than men.
- The routine use of many dietary supplements is discouraged in practice guidelines.
- The use of multivitamins, vitamin B6, folic acid, iron, magnesium, zinc, and copper was associated with a higher risk of mortality among older women in the current study.
- Conversely, calcium supplements were associated with a lower risk of mortality.
- Physicians need to analyze non-prescription therapies used by patients and warn them of potential harms associated with the use of supplements.