Vitamin D is a fat soluble vitamin. These dissolve in fats and oils and are stored in body fat. It is the only vitamin that is also a hormone, and comes in different forms. The two main ones are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). When choosing a supplement, look for vitamin D3. Both forms of vitamin D are well absorbed, but vitamin D3 is better at raising blood levels of vitamin D.
Vitamin D is unique as it is made during exposure to the sun. It is often called the ‘sunshine vitamin.’ When skin is exposed to sunlight, UVB rays help the body make vitamin D.
Unfortunately, this very important vitamin appears naturally in only a few foods, such as fatty fish. Milk is one source that has vitamin D added to it. (See the sidebar on page 13 for other food sources of vitamin D.) Most people find it difficult to get enough vitamin D from foods alone.
Vitamin D helps our bodies use calcium and other minerals to build and maintain strong bones and teeth. Recent research has found that vitamin D may have several other important functions in the body. It seems to help with some autoimmune diseases, particularly multiple sclerosis. Studies have associated higher vitamin D intake with a lower risk of rheumatoid arthritis. Too little has been linked to diseases including fibromyalgia, Crohn’s disease, and certain types of cancers.
Very exciting research has been done in the area of cancer prevention. Evidence suggests that those with higher blood levels of vitamin D have a lower risk of breast and prostate cancers, and nearly half the risk of colon cancer.
Vitamin D offers other benefits, especially for the elderly. It may prevent falls by increasing muscle and bone strength, and helping with balance. A few small studies have shown low vitamin D blood levels may contribute to poor mental function in the elderly. This one vitamin seems to affect many different systems in the body.
|Under 50 years of age:||200 IU/day|
|51 to 70 years of age:||400 IU/day|
|Over 70 years of age:||600 IU/day|
A maximum safe level is also recommended. The following amounts are not likely to pose a risk for almost all healthy people.
|Birth to 12 months:||1000 IU/day|
|Over one year old:||2000 IU/day|
One microgram (µg) of vitamin D = 40 International Units (IU)
Recommendations for vitamin D intake are based on age. The older you get, the more you need. Currently, Health Canada recommends the following amounts of Vitamin D.
If you live in a sunny climate, are under age 50, have light skin, and are in the sun regularly, you will likely get enough vitamin D from the sun. Most people living in Canada do not get enough vitamin D from the sun for the following reasons.
Vitamin D is not very plentiful in our diets. It appears naturally in fatty fish, shellfish and eggs from hens that have been fed vitamin D. In Canada, milk, margarine and infant formula are fortified with vitamin D, as are some yogurts, soy milks, orange juice and breakfast cereals.
If you eat a healthy diet including milk and fish, get out in the sun regularly, have light skin, and are under 50, you may not need vitamin D supplements. However, blood tests show that many people lack vitamin D, especially during the winter months.
Health Canada recommends that all breastfed babies and anyone over age 50 take 400 IU of vitamin D daily. The Canadian Cancer Society suggests that all adults take 1000 IU of vitamin D daily during the fall and winter months. Those at higher risk of vitamin D deficiency might consider taking 1000 IU daily all year round.
Most multivitamins contain 400 IU of vitamin D. You can find vitamin D by itself, usually in a 400 or 1000 IU amount, or combined with calcium and other minerals. Your pharmacist can help you choose from the often large variety of available products.
Many doctors now check blood levels of vitamin D (25-hydroxyvitamin D) to find those who are deficient. Some studies found that even people taking 400 IU of vitamin D are still lacking according to their blood levels.
Many researchers believe current guidelines for vitamin D are too low and that most people would benefit from higher intakes. Will recommendations and upper tolerable limits for vitamin D increase? This depends on research findings and whether side effects appear in those taking higher doses. A recent review article in the American Journal of Clinical Nutrition concluded that up to 10,000 IU of vitamin D a day is not toxic.
|Food||Serving||Vitamin D (IU)|
|Milk||1 cup (250 mL)||100|
|Margarine||1 tsp (5 ml)||25|
|Salmon||100 grams (3.5 ounces)||300 to 780 (depends on type of salmon)|
|Herring, pickled||100 grams (3.5 ounces)||680|
|Tuna, canned||100 grams (3.5 ounces)||50 to 80 (depends on type of tuna)|
|Reference: Canadian Nutrient File – Health Canada. One microgram (µg) of vitamin D = 40 international units (IU)|
Vitamin D is involved in the production and secretion of insulin. Obesity is a risk factor for developing type 2 diabetes. Some research shows that people with lower vitamin D levels are more likely to be obese or have type 2 diabetes. However, no reliable evidence shows that taking vitamin D supplements will prevent type 2 diabetes.
Infants who receive daily vitamin D supplements during the first year of life are thought to have a lower chance of developing type 1 diabetes later on. Still, more research is needed.
Chances are most people living in Canada are deficient in vitamin D. At the moment, more evidence is needed before routine blood screening for vitamin D deficiency would be established. If you think you are at risk, talk to your doctor, pharmacist or registered dietitian. Eat a healthy, well-balanced diet that includes good food sources of vitamin D.
Some researchers are urging the US and Canada to raise the safe dose of vitamin D from 2000 IU to 10,000 IU daily. Keep an eye on the research, as it may affect current daily recommended intakes for vitamin D. At this time, however, the recommendations from Health Canada are in the process of being changed, so be sure to talk to your doctor before taking higher than recommended dosages.