June 20, 2020
Data from the National Health and Nutrition Examination Survey (NHANES) of 2005-06 estimated the overall prevalence rate of Vitamin D deficiency (deficiency was defined as a serum 25-hydroxyvitamin D [25(OH)D] concentration of ≤ 20 ng/mL [50 nmol/L]) in the US to be 41.6% with the highest rate among older adults, nursing home residents, and African-Americans and Hispanics.
Does the high prevalence of vitamin D deficiency in the US matter at all?
There are numerous studies correlating low levels of vitamin D in plasma to increased risk of varying health maladies. Cancer, autoimmune disorders, general innate immunity, hypertension/other cardiovascular events, diabetes types 1 and 2, neuropsychiatric function, pregnancy outcomes, and all-cause mortality have all been cited as conditions potentially mediated by a patient’s Vitamin D status. Amidst a lack of consensus, either nationally or internationally, on how to deal with vitamin D deficiency at a population level, a large scale clinical trial was organized in order to uncover causal relationships in some of these cases. Vitamin D and Omega-3 Trial VITAL was a research study organized by Brigham and Women’s Hospital in Boston in 25,871 men and women across the U.S. investigating whether taking daily dietary supplements of vitamin D3 (2000 IU) or omega-3 fatty acids (Omacor® fish oil, 1 gram) reduces the risk for developing cancer, heart disease, and stroke in people who do not have a prior history of these illnesses. The findings from VITAL indicate that high-dose vitamin D does not lower the risk of developing cancer or cardiovascular disease in generally healthy men and women, although it does appear to lower the risk of cancer death. While the trial doesn’t address all therapeutic areas where vitamin D may be important, it certainly closes the door to much speculation.
Despite VITAL’s non-significant results, the debate around the importance of vitamin D supplementation has grown anew during the current COVID-19 pandemic. There has been recent commentary on the correlation between Vitamin D deficiency, Sars-CoV-2 PCR-positive patients, and poor COVID-19 outcomes. Several described mechanisms of vitamin D activity could support these observations: reduced viral replication, reduced pro-inflammatory cytokines, and increased anti-inflammatory cytokines. Vitamin D may also suppress CD26, a protein highly expressed on immune cells that binds to a structural protein on Sars-CoV-2 (see more here). While some researchers are calling for more randomized controlled trials and larger population studies to further understand these early observations, others are feeling urgency and arguing for Vitamin D dosing of at-risk populations as a public health intervention. As winter encroaches on the southern hemisphere, we may passively learn more about the role of Vitamin D in COVID-19 risk. But, should we wait to act?
– Casey Brooks, Jonathan Friedlander, PhD, Dac Nguyen, MD,PhD & Geoffrey W. Smith