How much vitamin d a day should one take?

Depends: Really depends on whether or not there is deficiency. As a supplement for osteoporosis prevention 800iu daily should be adequate. Otherwise any deficiency needs higher amounts with followups on vitamin d 25oh level. If you are concerned, your doctor can order this test.

It depends: The institute of medicine sets recommended dietary allowance(rda) at 600 iu for people ages 1-70 with safe upper limits for daily intake ages 9 & above at 4, 000iu. Many people take doses much higher than this if their levels are low but should do so under the supervision of their physician. If levels are normal 1, 000 iu is a good maintenance dose for adults. Vit D3 is better absorbed than d2.

Vitamin D intake: Vitamin d intake depends on what the level of serum 25ohd is in the blood. The average normal person should take at least 1000 u of vitamin D3 daily.