by Joy Y. Kiddie, MSc, RD

Vitamin D is a fat-soluble vitamin that is naturally present in very few foods and is added to others (especially dairy products), and is also available as a dietary supplement. Vitamin D is also produced in the body when ultraviolet rays from the sun makes contact with exposed skin and triggers vitamin D synthesis.

Vitamin D is essential for bone growth and bone remodeling but without sufficient vitamin D, bones can become thin, brittle, or misshapen. Together with calcium, vitamin D helps protect older adults from osteoporosis and children against rickets.

A Statistics Canada Report released in 2010 entitled Vitamin D status of Canadians as measured in the 2007 to 2009 Canadian Health Measures Survey indicated that while 90% of Canadians aged 6 - 79 years old have enough vitamin D in their blood for bone health, 10% (or roughly 3 million people) have concentrations considered to be inadequate (< 27.5 nmol/L) and 1.1 million Canadians (or 4% of the population) is actually vitamin D deficient; levels low enough to cause rickets in children and osteoporosis in adults.  The highest prevalence of deficiency occurred among men aged 20 to 39; with about 7% of this group considered vitamin D deficient.

The report's authors state that much higher concentrations (> 75 nmol/L) are considered optimal for overall health and disease prevention and according to this report only 1/3 of people in Canada are above this level known to be associated with a lower risk of breast and colon cancer, some cardiovascular disease and other diseases like multiple sclerosis.

Since there are only small amounts of vitamin D naturally occurring in foods such as oily cold-water fish (85 gm of light canned tuna contains 200 IU) and only a small amount of vitamin D is found in fortified foods such as milk (1 cup of milk contains 100 IU of vitamin D), many healthcare professionals encourage the use of vitamin D supplements. This is especially true in northern climates such as Canada which resides above the 49th parallel, as there are insufficient UV rays for 6 months of the year or more for adequate vitamin D synthesis. Additional factors such as the time of day, amount of cloud cover, smog, and the natural colour of one’s skin (melanin content) all affect the amount of vitamin D synthesis available during the other 6 months a year and of course, if one uses sunscreen, hats or clothing to protect oneself from the skin cancer risk, vitamin D will be inadequately synthesized.

So what about taking supplements…?  How much is recommended?

Health Canada indicates that the current maximum dose for most children and adults is 2,000 IU from all sources, however it is important to note that men with inadequate blood levels of vitamin D of 30 nmol/L would need to consume about 3,000 international units (IU) of vitamin D supplements per day to reach the more desirable 75 nmol/L level associated with lower cardiovascular and cancer risk.