I have written about the positive affects of vitamin D in previous posts

Vitamin D-Another Reason To Take It… Decrease Likelihood of Breast Cancer

Vitamin D, 70% of Kids are Deficient. Get 10-15 Minutes of Sun a Day!

Proper Vitamin D Levels Will Increase Your Chances of Living Longer

so hopefully you are supplementing… but with what?  If you have talked to me in my office in downtown San Francisco then you know I suggest D3.

A clinical trial demonstrated that supplementation with vitamin D3 was significantly more efficient at raising serum blood levels of the vitamin than vitamin D2.

Vitamin D refers to two biologically inactive precursors. Vitamin D3, known as cholecalciferol, and vitamin D2, known as ergocalciferol are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active ‘storage’ form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.

Source: Vitamin D3 Is More Potent Than Vitamin D2 in Humans