Vitamin A is probably best known for promoting and maintaining healthy eyesight, it also has other important functions as well. One of its major contributions is to improve the body's resistance to infection, it helps maintain healthy, smooth skin and mucous membranes. Essential for keeping the eyes healthy and moist, and helping the body to form blood, bones

Carotene is the plant derivative converted by our bodies into Vitamin A. As a potent immune-system booster and a powerful Antioxidant, it counters the effects of cell-damaging molecules called free-radicals--beta-carotene has an important role to play in human health.

Vitamin D 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. In addition, Vitamin D supplements may slow or even reverse some cancers.

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.