A British study found Vitamin D3 to be significantly more effective at raising total serum 25-hydroxyvitamin D than Vitamin D2 in the wintertime. During the 12 week trial, each group received biscuits or juice fortified with 600 IU (15 micro grams) of D2 or D3. The recommended daily allowance is 600 IU per day (800 for those over 70 years), but a another study cautions almost 25% of Americans are taking excessive doses of 1000 IU or more.
PositiveTip: As in most everything, balance is important in maintaining health and preventing disease.