How to (responsibly) get vitamin D

There's no better time than the summer solstice, the longest sunlit day of the year, to take in some rays and, with them, some complementary vitamin D. Just 15 minutes of sunshine on a clear day can help you produce up to 10,000 international units — and that could last you a while. Your body doesn't use the vitamin every day, so it gets stockpiled in fat tissues. Experts say its half-life up to 10 weeks, which means by the end of August, half of the vitamin D you produced on a day in June will still be in your body. The vitamin helps us absorb more calcium and phosphorus for strong bones and teeth, and it strengthens the immune system.

Related: Health benefits of vitamin D

Do: Go out between 10 a.m. and 4 p.m. (Your shadow should not be longer than your height.) When the sun is at too much of an angle, says Paul Veugelers, a professor of public health at the University of Alberta, UVB rays don’t penetrate the atmosphere. “You can sit and enjoy that beautiful 6 o’clock sunset, but the radiation is not sufficient to make vitamin D," he says. In Canada, vitamin D can only be synthesized in your skin when the UV index is above 3.

Don't: Lose track of the time. If you’re going to be outside for more than 15 minutes, slather on the SPF to avoid the risk of sunburn.

Do: Make sure at least 18 percent of your body — face, arms and hands — is exposed. People with dark skin tones have higher levels of melanin, the pigment that gives skin its colour, and require nearly five times more sun exposure to produce the same amount of vitamin D as light-skinned people. Melanin protects the skin from UVB damage, but as a result, less vitamin D is produced per minute.

Don't: Count on absorbing any in the winter. “Because we’re so far from the equator, we can make vitamin D only during spring, summer and early fall,” Veugelers says.

Do: Aim for 600 international units (IU) of vitamin D every day (for adults aged 19 to 50). It’s 800 IU for those over 50. Discuss sun exposure with your doctor to determine how much is safe for you.

Who needs vitamin D supplements?

Anyone who has tested positive for a deficiency. Approximately 32 percent of Canadians have levels that fall below 20 nanograms per millilitre (the amount that’s considered enough for healthy bones). Those at risk include people over 50 (the body’s ability to produce vitamin D declines with age), people with osteoporosis and melanoma, and those who can’t absorb it due to liver or bowel disease.