Fact is, low levels of Vitamin D makes us susceptible to a variety of illnesses (cancer, heart disease and even diabetes has been implicated), not the least of which is possibly multiple sclerosis, according to some experts. I personally have never had my levels tested, but since I wear sunscreen (we have a hot, tropical sun overhead most days of the year) and tend to avoid too much sun exposure (I have a little each day ranging from 5 minutes to half an hour), I take daily supplements of vitamin D3 (the active form of vitamin D).