Every Canadian should take a vitamin D supplement — and in my opinion, you should take far more than Health Canada recommends.

Vitamin D is crucial to bone health, but it also helps prevent or slow the spread of a surprising number of diseases and conditions, from multiple sclerosis to cancer. No matter how healthy your diet, you can’t get enough from food. And Canadians live too far north to deliver enough ultraviolet light from the sun, which produces most of our vitamin D.

Based on my research, I recommend that all adult Canadians take 2,000 IUs of vitamin D per day, and children should take at least 400 IUs in the winter. Those with darker skin are particularly at risk for low levels of D because darker skin absorbs less ultraviolet light from the sun. This is especially true when social stigma plays a role: it’s rarely talked about in public, but non-white people often tell me they avoid the sun because they don’t want to be darker.

Health Canada still recommends only 600 IUs a day, based on the belief that we only need a blood test result of 50nmol per litre. But is this optimal? Studies of lifeguards and people who live traditional ways of life in Africa show natural blood levels of vitamin D that are more than twice as high. Taking 2,000 IUs of vitamin D should raise your blood serum levels to about 80 nmol/L — still far lower than an outdoor lifeguard, who typically hits 130 nmol/L.

The more conservative experts worry that too much of a good thing could be harmful. Evidence is like a pendulum, sometimes good, sometimes bad. But until it settles, some fixate on risk, ignoring any benefit.

I have long argued that the real cause of confusion about vitamin D is the annual yo-yo of vitamin D throughout the year. Lots of it in summer, followed by none in winter is not normal for humans. Your body is designed by evolution to live in the tropics, and to have stable vitamin D levels. If you turn this powerful nutrient on and off, you may be harming yourself. That’s why I discourage the practice among some doctors to prescribe massive amounts of vitamin D all at once to raise a person’s level quickly.

Skeptics often point to the clinical trial showing that a group of vitamin D users developed more bone fractures and falls than those who didn’t supplement. That apparent bad news about vitamin D isn’t surprising if you recognize the vitamin D was given as one huge 500,000 IU dose, once a year. In my opinion, it was a poorly conceived study. Why on Earth would anybody give any nutrient just once a year?

If you’re old enough to remember the vitamin C hype (when this little miracle was supposed to cure cancer single-handedly and ward off colds), I don’t blame you for being skeptical of this new wonder vitamin’s powers.

But consider this: vitamin D is not a one-trick pony. It does more than just prevent rickets in babies. Its importance goes far beyond its ability to lay down new bone. Vitamin D is a raw material the body uses to communicate information between the body’s tissues and its cells. Think of vitamin D as if it were a blank piece of paper — useless on its own as a communications tool, but crucial as the carrier for the written word. When we don’t have enough paper, we can’t communicate and mistakes happen.

It’s the same with the body: a lack of vitamin D impairs biological communication, and disease happens. In cancer prevention, vitamin D is an important signal — stopping cells from “going bad” and also telling cells to slow reproduction. Cancer is in essence the out-of-control reproduction of cells that have “gone bad.”

That’s why higher levels of vitamin D are thought to cut your risk of cancer and so many other diseases. If you have cancer, heart disease, multiple sclerosis or another illness, it’s worth checking with the patient advocacy group that represents your disease to learn what levels they recommend. And don’t be afraid of a little sun!

Dr. Reinhold Vieth is a retired professor in the Faculty of Medicine’s Department of Laboratory Medicine and Pathobiology and Department of Nutritional Sciences. Doctors’ Notes is a weekly column by members of the University of Toronto’s Faculty of Medicine. If you have a question or comment for one of our experts, email doctorsnotes@thestar.ca .

How to get more vitamin D

If the UV index is higher than 3 (i.e. your shadow length is shorter than your height) lie on your front for 10 minutes, then turn over and lie on your back for 10 minutes. This should give you 10,000 units if you have white skin. Darker skin requires longer exposure.

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If you are dark-skinned and don’t want to tan, your D levels are likely to be half the levels of white Canadians. Consider at least 2,000 IUs of vitamin D in pills or drop form.

Take vitamin D3 supplements with food; digestive juices help absorption of nutrients.