Check out your vitamins. If vitamin D2 (ergocalciferol) is listed you may need to switch brands. Research has found that it is much less potent than vitamin D3(cholecalciferol). It's recommended that we get 1,000 IU of vitamin D per day through supplements or fortified foods. This can help head off a lot of health problems including osteoporosis and some kinds of cancer. Check your multivitamin and make sure you are getting the D you need.