A researcher measures skin colour in a University of Toronto lab. People with darker skin require longer sun exposure to make vitamin D. (CBC)More than a million Canadians are facing potentially serious health problems because their vitamin D levels are too low, according to a report released by Statistics Canada on March 23, 2010. Children who are vitamin D deficient are at risk of developing rickets — a softening of the bones that can lead to fractures and deformities. It's rare in Canada but among the most common childhood diseases in developing countries.

Not enough vitamin D can also lead to osteoporosis — reduced bone density that increases the risk of fractures — in older adults.

That Statistics Canada report also found that while most Canadians have enough vitamin D in their blood for bone health, only about a third are above the level believed necessary for overall health and disease prevention.

What is vitamin D?

Vitamin D helps the body absorb calcium thereby making bones stronger. Certain foods such as cow's milk and margarine are fortified with vitamin D and inexpensive supplements can help boost the body's vitamin D levels.

As breast milk doesn't contain sufficient levels of vitamin D, public health officials recommend that infants who are exclusively breastfed should take a supplement to prevent vitamin D deficiency.

People with darker skin tones are also often advised to take a supplement as they have more difficulty generating natural vitamin D from the sun's ultraviolet rays.

As well, patients with a reduced ability to absorb dietary fat, including people suffering from Crohn's disease, cystic fibrosis or liver disease, often have low vitamin D levels.

How much vitamin D do I need?

Osteoporosis Canada recommends daily supplements of:

• 400 to 1,000 IU for adults under age 50 without osteoporosis or conditions affecting vitamin D absorption.
• 800 to 2,000 IU for adults over 50.

The Canadian Cancer Society recommends Canadians take in 1,000 IU — 25 micrograms — of vitamin D every day. During the spring and summer, that can be accomplished through normal daily exposure to the sun. In the fall and winter months, a vitamin D supplement may be necessary.

Health Canada's guidelines remain at 400 IU — 10 micrograms.

A study released by the Institute of Health concludes that 600 IU of vitamin D meets the needs of almost everyone in the U.S. and Canada, although people 71 and older may require as much as 800 IUs per day because of potential physical and behavioral changes related to aging.

The study — commissioned by Health Canada and the American government — says there's still not enough evidence that vitamin D helps protect against cancer, heart disease, autoimmune diseases, and diabetes, but further investigation is warranted. The report notes that the risk of excessive vitamin D consumption —damage to the kidneys and heart — outweighs proven benefits.

How much vitamin D do you need to reach healthy levels if you are deficient?

While most researchers are recommending people take in 1,000 IU of vitamin D every day, it's estimated that people with low levels of vitamin D in their blood would need to take in 3,000 IU to raise their levels.

Osteoporosis Canada says people who need high doses to reach optimal vitamin D levels can take in up to 2,000 IU without medical supervision, but monitoring may be needed if higher doses are required. It takes about 18 minutes of midday sun exposure for your body to absorb that much vitamin D — or three times the daily recommended dosage in supplements, when sun is not an option.

How do I know whether my vitamin D levels are deficient?

Your doctor may recommend your vitamin D levels be tested. It's a simple blood test that costs between $32 and $93, depending on where you live. Demand for the test has skyrocketed in recent years. In Ontario, demand is up by 2500 per cent over the past five years. In B.C., demand is up 100 per cent in a year. B.C., Alberta, Saskatchewan, Manitoba, Ontario, and Newfoundland and Labrador are taking steps to limit the tests to people who have specific illnesses. B.C. and Manitoba have sent out reminders to doctors saying that healthy adults don't normally need to be tested.

What does the Canada Food Guide say about vitamin D?

The Canada Food Guide says men and women over the age of 50 should consume three servings of milk and alternatives along with a supplement equal to 10 micrograms or 400 IU of Vitamin D every day. One cup of milk has 100 IU of vitamin D. All other age groups are encouraged to have two cups of milk to ensure adequate vitamin-D levels.

Some companies have fortified their products with vitamin D but Health Canada notes that fatty fish and egg yolks are the only natural food sources.

Health Canada advises people to take a daily vitamin D supplement, as following the revised Canada Food Guide would only provide 200 IU of vitamin D a day.

Can't I just get mine from the sun?

While exposure to sun may be the best way to boost vitamin D levels — especially in the summer — this doesn't necessarily give sun lovers licence to tan. While being mindful of the threat of skin cancer, people should calculate how much time they spend in the sun depending on location, cloud cover, skin type, age and the amount of pollution in the area. Generally, doctors recommend that 10 to 15 minutes outdoors without sunscreen at least twice a week is adequate.

The Canadian Cancer Society, though, does not recommend that people rely solely on increasing their exposure to the sun to boost their levels of vitamin D. The society points out that there are other sources of vitamin D, including vitamin supplements, oily fish and fortified foods.

It also warns that — for some people — increasing exposure to the sun by even a few minutes a day could increase the risk of skin cancer. The society recommends that people consider a balance of vitamin D supplements and small amounts of sun exposure to maintain proper levels of the vitamin while keeping risks of skin cancer to a minimum.