Vitamin D is a fat-soluble vitamin and because of this, it may absorb more efficiently when taken with your biggest meal of the day. Research performed at the Cleveland Clinic involved 17 volunteers whose blood levels of vitamin D were low.
The subjects raised their blood levels of vitamin D significantly when taking it to coincide with their biggest meal of the day. Within a few months, it was found that their blood levels of Vitamin D had increased by 50 percent.
"The researchers measured blood levels of the vitamin at the start of the study and two or three months later. Participants took a range of doses, and the researchers divided them into three groups: less than 50,000 IU a week, 50,000 IU, and more than 50,000 IU. The daily doses ranged from 1,000 IU to 50,000 IU."
Vitamin D keeps bones strong, and also supports the immune system. It helps to prevent cancer and cardiovascular disease.
http://www.webmd.com/news/20100507/take-vitamin-d-with-largest-meal?ecd=wnl_wmh_051910