For years people took vitamin D for granted. We got it from the sun, and there was no doubt that we got enough. Besides, it didn't seem to be a particularly important vitamin. It may surprise you how much ideas like this have changed in the last few years. Vitamin D now appears to give more protection from cancer than any other vitamin. And that's not all. It also protects us from various autoimmune diseases, including MS, Crohn's disease, and autoimmune diabetes. It has also been shown to control the amount of inflammation produced by various cells, and as you likely know, excess inflammation can be a problem.
The evidence for protection from cancer is quite dramatic. Some of the forms of cancer it has been shown to protect us from are: bladder, breast, colon, ovary, and rectal. It has been shown, for example, that the northern states, which get considerably less sunlight (and therefore less vitamin D) as compared to the southern states, have much more cancer per capita.
There are actually two forms of vitamin D referred to as D2 and D3. We are concerned primarily with D3 as it is the most common; it is created in the skin by UVB light from the sun, and it is the main type we get from food. D2 comes mainly from mushrooms. The vitamin D we take in is in an inactive form. It is "preactivated" in the liver and final activation takes place in the kidneys. The preactivated form from the liver is the main type that circulates in the blood; it is called 25D.
The major reason that vitamin D is so important is that it is capable of regulating genes -- in other words, turning them on and off. This means that it sends a message to our genes to start or stop producing protein, and at least 1000 different genes are regulated and therefore under the control of vitamin D.
Why is this important? One reason (and perhaps the most important one) is that cancer is caused by cells where the "turnoff" switch has been compromised, and as a result, rapid and uncontrolled growth is occurring. And since vitamin D controls this growth in many types of cells it is obviously important -- so important that we have to be sure we have a sufficient amount of vitamin D circulating in our blood at all times. Studies have shown, however, that a large fraction of the population does not. A recent study in Europe of adolescent girls showed that 97% had low levels of vitamin D, with 35% of them "seriously deficient" in this respect.
How much vitamin D do we need? The RDI for adults is 200-600 IU, depending on age, but many researchers believe that this is far too low. They recommend 1000 IU/day, and some even suggest as much as 2000/day. But it's important to remember that vitamin D is fat soluble so it is possible to overdose. Studies have shown, however, that toxicity doesn't occur until about 40,000 IU and you could never overdose from food or sunlight. This would only be possible by taking very high doses of pills.
What is the best source of vitamin D? The UVB light from the sun is, of course, at the top of the list. You can get all you need in a day from about 15 to 20 minutes of sun (assuming it is overhead). I should mention, however, that sun screen block about 98% of the UVB. Since we get much less sun in the winter (particularly in the northern latitudes) it is important to take a supplement during the winter months.
What about foods? Cod liver oil is best, but I know it doesn't appeal to most people. Other good sources are: tuna, sardines, salmon, eggs, fortified milk, and orange juice.
Most of this article is adapted from my book "Feel Great Feel Alive: Seven Steps to Super Health and Fitness.
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