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Sunshine on bare skin is our main source of vitamin D, outside of our diet. However, many things can impact our level of sun exposure. The latitude where we live, seasonal change, cloud cover, smog, and sunscreen can all restrict the amount of vitamin D our body synthesizes. If you stay inside, have darker skin, wear clothing that covers most skin, or are more than 50 years old, you may be at risk of vitamin D deficiency and could benefit from a vitamin D3 supplement.
Vitamin D does many things: It helps our bodies absorb calcium, and promotes strong bones and teeth. It also helps maintain and support immune function. Importantly vitamin D deficiency is being noted as a risk factor in more and more health conditions.
Immune cells have vitamin D receptors, making vitamin D necessary for optimal immune function.
Without enough vitamin D, our bodies work far below their potential. Vitamin D deﬁciency can contribute to muscle weakness, aches, and pains, as well as our susceptibility to viral illnesses. Studies have shown that people with low levels of vitamin D were more likely to catch a cold or ﬂu. As we age, less vitamin D is converted to its active form, and as many as half of elderly people with hip fractures due to osteoporosis have low levels of vitamin D. Sufficient intake of vitamin D and calcium, along with a healthy diet and regular exercise, may reduce the risk of developing osteoporosis.
Vitamin D dosage 
|Age group||Recommended Dietary Allowance (RDA) per day||Tolerable Upper Intake Level (UL) per day|
|Children and Adults 9–-70 years||600 IU (15 mcg)||4000 IU (100 mcg)|
|Adults >70 years||800 IU (20 mcg)||4000 IU (100 mcg)|
These are the best natural sources of vitamin D3 in the Canadian diet:
Cooked mushrooms are a good source of vitamin D2. 
Fortified foods may also be a good source of vitamin D. Cow’s milk, for example, is required to be fortified in Canada. While goat’s milk and plant-based milks may be fortified, it is not required, so be sure to read nutrition labels and choose fortified whenever possible.
|Foods||Serving Size||Amount Vitamin D||% Daily Value|
|Trout||100 g (3.5 oz)||645 IU D3||81|
|Salmon*||100 g (3.5 oz)||570 IU D3||71|
|Herring||100 g (3.5 oz)||200 IU D3||25|
|Sardines||100 g (3.5 oz)||46 IU D3||6|
|Egg yolk**||1 egg||44 IU D3||6|
|Mushrooms (raw, white, exposed to UV light)***||100 g (3.5 oz)||366 IU D2||46|
|Fortified Foods||Serving Size||Amount Vitamin D||% Daily Value|
|Cow’s milk||250 mL (1 cup)||120 IU D3||15|
|Soy milk||250 mL (1 cup)||100–144 IU D3||13–18|
|Orange juice||125 mL (½ cup)||42 IU||7|
* Wild-caught salmon has much more vitamin D than farmed salmon.
** Eggs from pasture-raised chickens have much more vitamin D than conventionally raised chickens.
***Wild mushrooms contain much more vitamin D than canned mushrooms.
Vitamin D is available in supplement form as either vitamin D2 or vitamin D3. Vitamin D3 is best, because it’s already in the active, useable form, which is particularly important for immune support. With vitamin D2, your body needs to convert it to D3, and that is not always efficient, especially as we get older.
A vitamin D supplement will list either ergocalciferol (D2) or cholecalciferol (D3) in the ingredients. The term vitamin D is often used interchangeably with vitamin D2. Be sure to choose a vitamin D3 supplement, as it is already in the active, usable form. Vitamin D3 (cholecalciferol) is particularly important for immune support.
Because vitamin D is fat-soluble vitamin, it is best absorbed when taken with meals that contain a small amount of fat. It may also be best taken earlier in the day during sunshine hours rather than in the evening, as one small study showed that vitamin D level may affect melatonin levels. While this hasn’t been confirmed, it may be best to take vitamin D earlier in the day, to minimize the small chance of interfering with sleep.
The great news is that vitamin D levels can be improved through sun exposure, foods with vitamin D, and dietary supplements, helping to support healthy immunity.
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