By Sheela Sinharoy, Student Blogger
Living up to its name, the Advances & Controversies in Clinical Nutrition conference began with sessions exploring the many controversies and uncertainties around micronutrients. Some of the issues explored by speakers included potential cancer-preventive and cancer-promoting effects of micronutrients, as well as the challenges of micronutrient research. Ultimately, it seems, questions remain about all of these areas and more.
The evidence on micronutrients is often contradictory and confusing. For example, Dr. Joel Mason spoke about micronutrients such as folate, selenium, and vitamin E, each of which has been shown to be cancer-preventive in some trials and cancer-promoting in others. He explained that the effects of these and other micronutrients may follow a curve in which they are protective in amounts up to a maximal optimal dose, after which the effect plateaus and may even become detrimental. However, even if this is the case, the optimal dose of each micronutrient remains unclear.
Similarly, other speakers discussed dietary supplements and their relationship to all-cause mortality, cardiovascular disease, cancer, and neurological diseases. Dr. Eliseo Guallar discussed meta-analyses of dietary supplements and concluded that most supplements have no effect or, in the worst cases, actually cause harm. He explained that there is very little evidence on multivitamins, because most studies focus on individual supplements rather than on multivitamins.
A further complicating factor is that different populations have different nutrient needs. Addressing this issue, Dr. Johanna Dwyer exhorted the audience to “mind the gaps” in micronutrient intakes in the US population. For example, she shared data indicating that women ages 20-29 years old in the US have borderline insufficient intakes of iodine. This has serious implications given the importance of iodine during pregnancy for neurological development of the fetus. Thus, special recommendations on iodine may be needed for women in this age group. Other sub-populations at risk, according to Dr. Dwyer, may include exclusively breastfed infants and some elder populations, especially those with heart failure.
Of course, more research is needed to better understand the role of micronutrients and dietary supplements, especially in the prevention of age-related chronic disease. However, as pointed out by multiple speakers, both observational studies and randomized controlled trials (RCTs) are fraught with challenges. Observational studies have a large potential for bias, and the observable effects will be small. At the same time, RCTs are problematic because, unlike pharmaceutical trials, there is never a true placebo group when studying micronutrients. As Dr. Balz Frei pointed out, everyone has some level of the essential micronutrients; at best, researchers can plan to measure the baseline levels and use those as inclusion or exclusion criteria for the study.
The goal of nutrition research, at least for many of us, is to generate evidence that can be used to guide others – whether clinicians, policy makers, or other program implementers – in making informed decisions. However, the current evidence base on micronutrients does not lend itself to clear guidance. One suspects that this will remain an area of advances and controversies for quite some time.