Nutrition Bytes: March 2023

Long-Term Vitamin D Supplementation Linked to Lower COVID Infection & Deaths

A 2022 study1 published in Nature Scientific Reports builds on the mountain of evidence linking vitamin D supplementation with protection from COVID-19 and improving the immune response and outcomes during infection. Specifically, researchers found that long-term vitamin D3 supplementation reduced the risk of COVID-19 infection and death in a large group (over 200,000) of United States Military veterans.

In the study, researchers analyzed data on veterans who supplemented with oral vitamin D3 or who did not supplement for a year prior to the pandemic and for at least nine months during the pandemic. Results revealed that supplementing continuously (compared to not supplementing) with vitamin D3 was linked to a 20 percent reduction in COVID-19 infection risk during the study period. Those receiving the greatest reduction in infection risk included those receiving higher doses of vitamin D3, as higher doses are more likely to increase blood levels to those necessary for protection from infection.

African American supplemented veterans also experienced greater reductions in infection risk compared to white patients (29% decrease versus 18% decrease). Although the exact mechanism for this was not determined, such results point to vitamin D supplementation as a useful tool in closing racial disparities in COVID-19 outcomes. Finally, among all veterans supplementing with vitamin D3, death within 30 days of COVID-19 infection was also 33 percent lower.

The researchers went on to say that if they extrapolated their results to the entire US population in 2020, “There would have been approximately 4 million fewer COVID-19 cases and 116,000 deaths avoided.” These findings, combined with the fact that approximately half the US population experience vitamin D insufficiency and deficiency, provide further reason to get your blood levels of vitamin D checked and maintain optimal levels of this important nutrient through supplementation. Research and experts suggest that optimal blood levels of vitamin D are between 30-65 ng/mL.

Fish Oil Improves Attention and Processing In Children

Child wearing a stethoscope and playing with a stuffed animalA study2 conducted in July of 2022 found that fish oil supplements improved attention and cognitive processing in children. Fish oil supplements provide two important omega-3 fats—EPA and DHA—which are known to play important roles in supporting brain function, including inhibition, attention, and problem solving. In the diet, EPA and DHA are mostly obtained from cold-water fish such as salmon and sardines, but since most children don’t eat these foods, researchers wanted to study the effects of a daily fish oil supplement (concentrated in DHA) taken for 12 weeks in children 6-12 years old. The researchers separated 120 cognitive healthy children into three groups, including a low-dose DHA (260mg) group, a high-dose DHA (520mg) group, and a placebo group. The participants were subjected to a series of computerized cognitive tests at the start of the study and at the end of the 12-week study period. While previous studies have measured the effects of fish oil on cognitive function, this study is unique because it also assessed real-time electrical brain activity with a non-invasive measurement device.

At the end of the 12-week period, the researchers found a significant increase in brain activity for the high-dose DHA group during all the cognitive function tests, indicating an improvement in processing of information and working memory. Additionally, there was a dose-dependent response effect of fish oil on brain activity during the cognitive tests, indicating improvements in attention and cognitive processing with higher doses of DHA concentrated fish oil.


  1. Gibbons JB, Norton EC, McCullough JS, et al. Association between vitamin D supplementation and COVID-19 infection and mortality. Sci Rep. 2022 Nov 12;12(1):19397. doi: 10.1038/s41598-022-24053-4.
  2. Sittiprapaporn, P., Bumrungpert, A., Suyajai, P., & Stough, C. (2022). Effectiveness of Fish Oil-DHA Supplementation for Cognitive Function in Thai Children: A Randomized, Doubled-Blind, Two-Dose, Placebo-Controlled Clinical Trial. Foods, 11(17), 2595.