VITAMIN D
Technically not a "vitamin," vitamin D is in a class by itself. Its metabolic product, calcitriol, is actually a secosteroid hormone that targets over 2000 genes (about 10% of the human genome) in the human body. Current research has implicated vitamin D deficiency as a major factor in the pathology of at least 17 varieties of cancer as well as heart disease, stroke, hypertension, autoimmune diseases, diabetes, depression, chronic pain, osteoarthritis, osteoporosis, muscle weakness, muscle wasting, birth defects, periodontal disease, and more.
If well adults and adolescents regularly avoid sunlight exposure, research indicates a necessity to supplement with at least 5,000 units (IU) of vitamin D daily. To obtain this amount from milk one would need to consume 50 glasses. With a multivitamin more than 10 tablets would be necessary. The skin produces approximately 10,000 IU vitamin D in response 20–30 minutes summer sun exposure—50 times more than the US government's recommendation of 200 IU per day!
How To Get Enough Vitamin D
There are 2 healthy ways for adults to insure adequate levels of vitamin D:
* regularly receive midday sun exposure in the late spring, summer, and early fall, exposing as much of the skin as possible (being careful to never burn).

* take 5,000 IU per day