Our bodies need vitamin D to absorb calcium — the major building block of bone. It boosts the body’s ability to absorb calcium by up to 30-80%. Vitamin D becomes especially important as we get older, when calcium is less efficiently absorbed. Together, calcium and vitamin D can prevent osteoporosis — a condition where bones become thin, brittle and break easily.

Vitamin D is often called "the sunshine vitamin," since our bodies can actually produce it themselves when exposed to sunlight. In the summer, having our arms, face and hands out in the sun for just 15 minutes a day can make a lot of vitamin D. Unfortunately, the sun may not be the safest or most reliable way to get enough of this vitamin. Using sunscreens to prevent skin cancer blocks the rays needed to produce vitamin D. Dark-skinned people absorb less sunlight than those with light skins, putting them at risk of vitamin D deficiency. Also, many people, especially the elderly, are at risk as they spend more time indoors. Finally, the long, cold and dark Canadian winters mean that the skin’s vitamin D production shuts down from early October until late March every year.

So how can we get enough vitamin D — and just how much do we need?

• Babies, children and adults need 400 IU (international units) per day
• Older adults should get between 400 and 800 IU daily.

In Canada, a glass of milk (250 mL) is enriched with 100 IU of vitamin D, making it a good source of this nutrient. Small amounts of vitamin D are in margarine, eggs, chicken liver, salmon, sardines, herring, mackerel, swordfish and fish liver oil. It may be hard to get enough vitamin D from food alone, though, so you may opt to take a supplement. Remember that most multivitamins contain 400 IU of vitamin D, which is enough for most people. Don’t be tempted to take higher doses — too much vitamin D can lead to loss of calcium from bone, too much calcium in the blood, and kidney problems.

It’s especially important that babies and children get enough vitamin D. Kids who are short on this vitamin can get rickets, a disease affecting bone development. Infant formulas are already fortified with vitamin D, so bottle-fed babies don’t need supplements. Breastfed babies, on the other hand, may need a supplement of 400 IU per day (800 IU per day is recommended for babies in northern communities) since breast milk is usually low in vitamin D. Breast milk is still the perfect food for babies but, if you’re breastfeeding, talk to your doctor about whether your baby needs extra vitamin D.