Studies about vitamin D and immunity:
Influence of Vitamin D Status on Respiratory Infection Incidence and Immune Function During 4 Months of Winter Training in Endurance Sport Athletes (2013)
Conclusion: In a 4-month winter study of 225 endurance athletes it was found that those with the lowest vitamin D levels suffered more upper respiratory tract infections compared to those with optimal vitamin D levels. Athletes with good vitamin D levels who did get sick also tended to recover faster than the deficient athletes.
Randomized Trial of Vitamin D Supplementation and Risk of Acute Respiratory Infection in Mongolia (2012)
Conclusion: In a randomized control trial involving 247 Mongolian schoolchildren during winter, those given a measly 300 IU of vitamin D daily through vitamin D-fortified milk experienced fewer acute respiratory infections compared to school children given non-fortified milk.
Conclusion: In a year-long study of 41 NCAA division 1 athletes, it was found that those with lower vitamin D levels suffered more illnesses compared to athletes with higher vitamin D levels.
Serum 25-Hydroxyvitamin D and the Incidence of Acute Viral Respiratory Tract Infections in Healthy Adults (2010)
Conclusion: People who maintain adequate vitamin D levels have a significantly lower risk of developing viral respiratory tract infections.
Randomized Trial of Vitamin D Supplementation to Prevent Seasonal Influenza A in Schoolchildren (2010)
Conclusion: In this randomized, double-blind, placebo-controlled trial involving 334 school children over a 4-month period, the vitamin D group experienced nearly 50% fewer colds and even fewer asthma attacks compared to the placebo group.
Association Between Serum 25-Hydroxyvitamin D Level and Upper Respiratory Tract Infection in the Third National Health and Nutrition Examination Survey (2009)
Conclusion: People with higher vitamin D levels experience fewer upper respiratory tract infections.
Conclusion: “Low vitamin D levels were associated with a 5-fold increased risk for progression to tuberculosis” in a study of Pakistan tuberculosis cases.
Conclusion: Tuberculosis rates were higher among people with lower vitamin D levels in this study.
Conclusion: Regular sun exposure increases immunity in children.