Many people suffer from subclinical deficiency, meaning there are no obvious symptoms signaling an insufficient amount of the vitamin. So, to make sure you are getting enough D, Zeratsky recommends taking a multivitamin, especially people living in cloudy climates or those who religiously wear sunscreen. "We need more research to decide what the optimal level of vitamin D really is, but in general, a multivitamin is a good idea as a safety net in addition to dietary sources," says Zeratsky. Overdosing on vitamin D is possible, but not likely. According to the Institute of Medicine, the upper limit for intake is 2000 IUs. Still, if deciding to take a supplement, it is always best to consult a doctor.