Most people don’t need to take extra vitamin D and calcium supplements — and taking too much can actually be harmful. This is because both vitamin D and calcium can build up in the body, causing serious health problems. Vitamin D is fat-soluble, which means that it is stored in the fat cells of the body and can thus accumulate to toxic levels over time, causing nausea, fatigue, deafness and bone loss. Likewise, too much calcium in the body can impair kidney function and lead to constipation, nausea and even a coma.