You’ve probably already heard that vitamin D keeps your bones and teeth healthy, and helps protect against some cancers.

Now, new research, led by Dr. Pamela Goodwin at Mount Sinai Hospital's Samuel Lunenfeld Research Institute in Toronto and released by the American Society of Clinical Oncology, indicates that vitamin-D deficiency may result in higher-grade breast cancer tumours and almost double the likelihood that the cancer will spread, or metastasize.

But as the Globe and Mail’s Martin Mittelstaedt points out, dose recommendations still vary widely.

For healthy women aged 31 to 50, Health Canada recommends 200 international units (IU) daily. The Canadian Cancer Society recommends 1,000 IU for fair-skinned people during the fall and winter, and for dark-skinned people year round. Goodwin cautiously suggests 800 IU a day. Health Canada warns against exceeding 2,000 IU.

Fortified milk, eggs, fish and fish oils all deliver vitamin D, but a supplement would probably be required to reach some of the latter suggestions (in the fall and winter at least). One place you don’t want to get your vitamin D: a tanning bed. Keep wearing sunscreen for most of the day, too.

Personally, I take a 1,000 IU vitamin D supplement every day. But the best person to ask, of course, is your doctor.