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What You Need to Know About Vitamin D

Chances are, you have probably been hearing about the “sunshine vitamin” in recent years; how it promotes your health in various ways and how we obtain this vitamin from the sun. It seems very evident from most research that we don’t seem to be getting enough. What do you really know about this vitamin and how it works inside our body?

Vitamin D is provided to us via either sun exposure, food or supplements and is biologically inert. This means it must undergo two conversions in the body, first from the liver and then from the kidney before it is physiologically active and can be utilized. This active form is known as calcitrol.

Apart from promoting a good mood, vitamin D’s most important role is probably that of its ability to remodel bone. Without it, bones will become very thin and brittle, even misshapen. It prevents rickets in children and osteomalacia in adults. It can protect older adults from osteoporosis in conjunction with calcium.

In addition, vitamin D promotes calcium absorption at the gastrointestinal system as well as reabsorption of calcium at the kidneys. Both result in more calcium in the body to add to bone. Apart from this, it is also important in promoting cellular growth, neuromuscular and immune function.

Vitamin D has also been shown to have a protective effect against colon, prostate and breast cancer and decrease inflammation in your body. There is even some data recently to suggest that vitamin D plays a role in type 2 diabetes, hypertension, and multiple sclerosis.

So are you deficient?

There are a few ways of testing for vitamin D status in the body. The most common is testing for the serum concentration of 25 hydroxyvitamin D (the first converted stage by the liver, and inactive form). This value reflects the vitamin D produced by the skin and that is obtained by food and supplements. It is not yet clear however, to what effect this relates to our health status or outcomes. Furthermore, serum levels do not indicate the amount of vitamin D that is stored in the tissues.

The second method of testing is to test for the serum concentration of 1, 25 dihydroxyvitamin D (the active form of vitamin D, having been converted by both the liver and kidney). This form has a very short half life which makes it difficult to test for and get accurate results.

There is considerable discussion as to whether testing for an inactive form of vitamin D (25 hydroxyvitamin) is associated with any sort of deficiency (ie. Rickets), or is indicative of bone health or optimal health. There are further problems with testing for vitamin D status which relates to how each laboratory conducts the analyses, depending on the lab it may lead to false values.

Daily reference values for vitamin D intake include a tolerable upper intake level of 4000IU/day for adults and children 9 years of age and older.

More on Vitamin D

Vitamin D Containing Foods:

Few foods contain vitamin D in nature. The flesh of fatty fish such as salmon, tuna and mackerel are among the best sources. Some small amounts are found in beef liver, and egg yolks. These foods contain mostly the active form of vitamin D. Some mushrooms will also provide some vitamin D, but in an inactive form.

Fortified foods such as dairy milk, almond milk, soy milk, and orange juice provide the most vitamin D in our diets. In Canada roughly 40 IU’s of vitamin D are in 100ml of liquid milk products. Even cereals often contain added vitamin D now! Cod liver oil contains the highest per serving amount of vitamin D at over 1000IU per serving!

Sun Exposure

The sun is an essential part in us forming vitamin D within our bodies. You probably have also heard that we are not getting enough sun exposure to provide us with sufficient vitamin D. But what if you live in a tropical area or travel there regularly? Surprisingly, geographic latitude has not consistently predicted average vitamin levels in a population. This suggests that there are ample opportunities to form vitamin D and store it in the liver and fat even in the northern latitudes. It is also known that most people do meet at least some of their vitamin D needs through exposure to sunlight (specifically UV–B rays) but it is essential that light penetrates uncovered or unprotected (i.e. no sunscreen) skin. When sunscreen is used correctly an SPF of 15 deflects about 90 percent of the UVB rays. Remember, that although these rays do produce the helpful vitamin D, they also can induce sunburn, DNA damage, and skin concerns. You cannot separate the wanted from unwanted effects when it comes to sun exposure. Therefore, it is recommended you protect your skin from excessive exposure and sunburn and obtain vitamin D through other methods (i.e. supplements and food).

Groups at Risk of Vitamin D Deficiency

Infants: Breastfeeding is by far the best way to ensure your baby gets the nutrients it needs; however, vitamin D status in the mother is directly correlated to vitamin D status in breast milk. It is essential that mothers supplement with vitamin D during breast feeding. The government of Canada suggests that 400IU/day in infants be supplemented.

Older adults: Older adults cannot synthesize vitamin D as well from their skin. They are likely to spend more time indoors as well as have lower nutritional intake from their diet. Since vitamin D is essential to bone health and reduction of risk of osteoporosis, it is important to make sure these levels are kept high.

People with dark skin: Dark skin means there is more of a pigment melanin in the epidermal layer. This can reduce the skins ability to produce vitamin D from the sun, although there is no conclusive evidence that darker skinned peoples suffer more health consequences. Studies that have been done actually suggest that there are lower rates of osteoporosis among those of African Amercian ancestry compared to those that are Caucasian.