IFNG and vitamin D deficiency: This is important since a recent meta-analysis indicates that 25 nmol/L is a critical threshold of vitamin D deficiency associated with elevated risk for acute respiratory infection (7) and other studies demonstrate that vitamin D supplementation alters circulating IFN-g and IL-10 levels in individuals with vitamin D insufficiency (20), suggesting that vitamin D supplementation exerts most effect on human immunity in the context of severe vitamin D deficiency.