In fact, the FDA cautioned Americans not to exceed 400 IUs daily of vitamin D3 as it would accumulate and cause toxicity.  We now know that most people are taking 5000 IUs or more of vitamin D3 without significant side effects.  Experts around the world are demanding that the recommended daily level of vitamin D3 be increased to a minimum of 1000 to 2000 IUs of vitamin D3 daily.  As a side note, a recent study of three groups of pregnant women were put on different levels of vitamin D3.  One group 2000 IUs daily, a second group 4000 IUs of vitamin D3 daily and the third group 6000 IUs daily.  The study lasted throughout the pregnancy and for an additional two years after the infant was born.  The ladies receiving 6000 IUs of vitamin D3 daily had less complications than the other two groups.  The group receiving the highest level of vitamin D3 had less gestational diabetes and high blood pressure, less toxemia, less post-partum depression, less premature births and fewer of the infants were born through C-section.  The infants upon birth were given 1000 IUs of vitamin D3 daily.  At their second anniversary, there was 78% less juvenile diabetes than the other two groups.