Strengthens the bones and teeth and also fosters normal muscle contraction and nerve function. It is also useful for promoting immunity and blood cell formation. Vitamin D helps to reduce the risk of falling associated with postural instability and muscle weakness. Falling is a risk factor for bone fractures among men and women 60 years of age and older.
Numerous studies link vitamin D and influenza, as well as vitamin D and respiratory infections more generally. This vitamin up-regulates genetic expression of various endogenous antimicrobial peptides (AMP), which exhibit broad-spectrum microbicidal activity against bacteria, fungi, and viruses. Susceptibility to influenza including H1N1 is reduced with higher levels of sun exposure or vitamin D supplementation. Seasonal variation of vitamin D levels in humans can help explain the seasonality of flu epidemics.