Vitamin D Where You Live
The darker a person's skin, the more difficult it is to get vitamin D from sunlight. Fair-skinned people might be willing to risk the 10 to 15 minutes they need to get enough. But there's still a problem. Unless you live south of a line from Los Angeles to Columbia, S.C., there isn't enough sunlight year round to produce all the vitamin D you need. Most people need other sources.
How Much Vitamin D Do You Need?
How much vitamin D you need depends on your age and risk factors. Recommendations for daily adequate intake, which are being reviewed, are 200 IU for adults under 50, 400 IU for ages 51 to 70, and 600 IU for ages 70 or over. Most experts, though, feel those levels are too low. The National Osteoporosis Foundation recommends 800 to 1,000 IU for all adults over age 50.
D2 or D3? That's the Question.
Vitamin D is available in supplements in two forms: D2 and D3. Both forms are effective, and either can be taken to ensure adequate levels of vitamin D. But 2 is not equal to 3. D3 is the kind of vitamin D the body makes, and recent studies suggest that D3 can be up to three times more effective in raising the vitamin D level quickly and staying longer.
Please consult with your physician before you take any dietary supplements.

Portions of the above content were provided by www.webmd.com