Human: My doctor says I should start taking vitamin D supplements. What are vitamin D supplements and are there any side effects? Assistant: 
Vitamin D is a fat-soluble vitamin that helps the body absorb calcium and phosphorus, which are essential for bone health. It can also help with muscle function, immunity, and inflammation. There are several forms of vitamin D, including D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D3 is produced in the skin when it is exposed to sunlight. Vitamin D2 is usually derived from plant sources such as fortified milk or eggs. The recommended daily intake for adults is 600 IU per day. Side effects associated with high doses of vitamin D include nausea, vomiting, constipation, dizziness, headache, and weakness.