Dr. Louise Parker, an epidemiologist at Dalhousie University in Halifax, Nova Scotia, says vitamin D may be the "new aspirin" but it works in very complicated way, including changing the way cells work.

There is medical speculation that vitamin D may block cancer cell proliferation or improve immune system functions, but its role is not fully understood, Parker says.

The Canadian Cancer Society recommends that during the winter, Canadians take at least 1,000 units a day of vitamin D, Parker says.

Parker says that 1,000 units a day is well beyond what people can obtain from food sources -- it appears in fatty fish like salmon and sardines, cod liver oil and egg yolks.