Vit D critical for immune system maintenance - cold/flus in winter, lack of Vit D
COMT (dopamine gene) is also influenced by your VDR Taq gene status - which makes dopamine from Vitamin D.
Vitamin D is best known for its role in calcium metabolism and bone health, but new roles are continually being discovered for it, including roles in mental health, blood sugar regulation, the immune system, and cancer prevention. Yet standard modern advice -- take cholesterol-lowering drugs, avoid the sun, eat a low-cholesterol diet -- combined with a recommended daily intake of vitamin D that is only a tenth of what many researchers believe to be sufficient all seems to pave the way for widespread vitamin D deficiency.
Daily dose in excess of 40,000 IC shown to cause an elevation in the blood calcium level (hypercalcemia), the first manifestation of vitamin D toxicity
Sunshine - 20 minutes sunbathing per day, light skinned absorb 20,000 IUs then synthesis shuts down for the day
Vit D3 is only form absorbed. D2 is useless
Don't Get A Flu Shot Article