We need UVB light is necessary to make vitamin D. The amount of exposure to sunlight is reviewed. The production of vitamin D is also reviewed. Organs that are prone to cancer convert the circulating 25 hydroxy vitamin D to the hormonal form of 1, 25 dihydroxy vitamin D (calcitriol), which is 1000 times more effective in fighting cancer. Too much of the hormonal form can lead to depositing calcium into our arteries and make us prone to heart attacks and strokes. Food sources of vitamin D are eggs from chickens exposed to sunlight, fish (from plankton), and some meats. Mushrooms irradiated with UVB can have substantial amounts of vitamin D. High levels of vitamin A blocks the receptor sites of vitamin D in bone and lead to osteoporosis. This is why taking more than 5000 IU of vitamin A per day is associated with osteoporosis.
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