Dietary Supplementation and RCTs: Context is Important
Vitamin A supplementation prevents death and illness in children 6 mo to 5 years of age. An editorial in JAMA published today states that further randomized-controlled trials (RCT) in children would not be ethical given the well-established benefits of supplementation – a 24% reduction in child mortality. Pretty strong stance on use of dietary supplements.
This statement is derived from a meta-analysis of 43 vitamin A supplementation trials including more than 215,000 children published in BMJ. Mayo-Wilson and colleagues demonstrate the importance of vitamin A for growth and development – the essentiality of micronutrients for health. When dietary intakes are suboptimal, supplementation is an important means to acquire essential vitamins and minerals.
In contrast, there have been numerous headlines this past week saying supplements are wasteful, if not dangerous to your health. What? Which message is right? Should I use supplements or not?
Measuring the impact of nutrient supplementations with RCTs is difficult. A control placebo group does not exist. Everybody has some level of nutrient intake. In most RCTs, participants have an exceptional interest in health and nutrition or they wouldn’t volunteer. Are their lifestyle behaviors typical of others? Does their interest wane with time?
In the vitamin E and prostate RCT, adherence to the treatments, measured by pill count, fell to 65% in year 5. This suggests a diminishing interest by volunteers. At what point does lack of compliance render the study meaningless? Is it valid to collect data almost two years after the study ends and draw conclusions on vitamin E use and prostate cancer?
RCTs seem to be most useful in understanding nutrient-health relationships when nutrient intakes by the population are low, such as with vitamin A and low- and middle-income 6mo to 5 year olds. Then researchers are testing the impact of added vitamin A against a low vitamin A dietary background. In subpopulations with higher socioeconomic status who have options to choose healthier diets and self-supplement, such as the SELECT study, RCTs have limited value. The men were asked to take 400 IU vitamin E daily. Compliance fell during the study. Vitamin E self-supplementation was much more prevalent in 2000 than 2010. Is vitamin E status and prostate cancer really understood? When discussing the value of supplementation, context is important.
Nutrients are not magic bullets which can prevent or mitigate disease. They are essential for life but more is not necessarily better. As written by two UI dietetic students, SeAnne Safaii and Tabitaha Sonnen, “Good nutrition is about balance.”