A report from the US Preventive Services Task Force (USPSTF) was published recently (February 25 issue) in the Annals of Internal Medicine. This report focused on the use of vitamin, mineral, or multivitamin supplements for the prevention of cardiovascular disease and cancer. The conclusions of the task force were largely that the current evidence is insufficient to assess the benefits and harms of most single-nutrient and multivitamin/mineral supplements with respect to prevention of cardiovascular disease and cancer, although they did issue caution for vitamin E and beta carotene supplements. For the most part, experts at the Linus Pauling Institute (LPI) at Oregon State University agree with these findings, and state they are supported by an evidence-based review of the scientific literature on vitamin and mineral supplements.
One of the key words in the USPSTF report is “insufficient.” Although the report does not thoroughly examine the limitations prevalent in vitamin and mineral supplement trials, researchers at the LPI have already published their conclusions that many large, clinical trials of vitamin supplements employ imperfect or inappropriate methodologies that render them largely useless in determining the real value of these micronutrients on human health. LPI analysis of the literature also shows that the conventional randomized controlled trial (RCT) design – although the “gold standard” to evaluate the effects of pharmaceutical drugs – is strongly biased against showing benefits of essential nutrients.
Unfortunately, the report combines a very diverse set of nutrient interventions together into their recommendations. While a review of the scientific literature can be very powerful when the individual studies are conducted with standardized methodology and endpoints, lumping together studies of completely different designs and datasets leads to a dilution of the power of the all studies involved in the review and significantly weakens the overall conclusions. The USPSTF report acknowledges that limitations exist in the research conducted to date. To quote the report: “A general lack of standardized methods to determine relevant serum nutrient levels, agreement on thresholds for sufficiency and insufficiency, or predictive validity of current mechanistic models further hinders progress in understanding potential benefits of dietary supplements.” In general, this echoes the LPI message, and highlights all of the relevant points (or fatal flaws) that have limited micronutrient research.
Nevertheless, it is worth noting that much of the US population does not meet intake recommendations for many vitamins and minerals, including the vitamins A, C, D, E, and K, and also calcium, magnesium, and potassium. It is also important to note that when these gaps are addressed by the long-term use of multivitamin/mineral supplements, some disease protection has been found. The largest and longest trial on multivitamin use found a significant reduction in total cancer incidence in male physicians. This RCT also found a significant reduction in total cataract incidence. The fact that these conclusions were reached in a health-conscious group (medical doctors) and conducted with the conventional RCT design suggests that the results of these studies (and the effect of the multivitamin/mineral supplements) may be greater in the general population.
LPI has been on the forefront of supporting the use of multivitamin/mineral supplements to support a normal diet. To quote Balz Frei, director and endowed chair of the LPI: “The persistence of poorly controlled studies within the field of micronutrient research undermines efforts to recommend multivitamins/minerals as a safe, economical, and effective means of promoting health. It not only weakens efforts to fund additional, well-designed RCTs necessary to establish definitive health claims that are desperately needed, but serves to confuse and detract from the real issue of nutritional inadequacies that are of great public concern.” He goes on, saying that: “Taking a daily multivitamin/mineral supplements is a safe, affordable, and simple way to help fill nutritional gaps and improve micronutrient status of Americans. Adequate micronutrient status is needed for normal biological function and metabolism and to support good overall health.”