About 40% of Americans have insufficient vitamin D levels. Recent studies demonstrate that vitamin D boosts cold weather immunity.
References.
Impact of Vitamin D on Autoimmune Risk
A major clinical trial showed that supplementing with vitamin D3 and omega-3 reduced incidence of autoimmune disease by 25%-30%.
Human Autoimmune Study, Impressive Study Size and Design, Impact of Longer-Term Vitamin D Supplementation, Serendipitous Benefits of Vitamin D + Omega-3s, References.
Vitamin D’s Winter Immune Benefits
Clinical trials show that vitamin D decreases rates and severity of viral respiratory tract infections. More than 70% of Americans have either deficient or insufficient vitamin D blood levels.
Impact on Immune Function, Vitamin D’s Immune Benefits, Vitamin D and Viral Illness, Vitamin D’s Protective Actions, Oral Vitamin D Reduces Risk, Summary, References.