This overlooked vitamin can help grow muscle, but don’t overdo it
Vitamin A plays an important role in maintaining the health of your eyesight, as well as your skin, teeth, bones and mucous membranes, including your respiratory tract. This important vitamin can improve your resistance to infection and assist in the growth and repair of body tissues, including muscle. Brand new research shows that vitamin A is critical for energy production in the body.
Yet megadoses of vitamin A can be harmful in some populations. High doses can lead to hip fractures in older men and women and, if too much is taken by pregnant women, it can increase the risk of birth defects. Unless you’re pregnant or elderly, though, you have little to worry about. Sure, if you routinely take 25,000 international units (IU) of vitamin A per day for several months, toxicity may develop, along with liver disease, because the body cannot easily flush out excess vitamin A. That’s because it’s fat-soluble and gets stored in fat cells. 
The body itself can make vitamin A from certain carotenoids, especially beta carotene, which is found in orange, red and leafy green vegetables and in fruits. Beta carotene is basically two vitamin A molecules bound end-to-end. What’s great about beta carotene is that if the body’s vitamin A sources are low, then and only then does it convert into active vitamin A.
The National Academy of Sciences’ Institute of Medicine, which sets the recommended daily allowances (RDA), suggests that men should strive for 3,000 IU of vitamin A per day. For women, the standard is 2,330 IU of vitamin A. The safe upper limit for both men and women is 10,000 IU of vitamin A. If you take a supplement, such as a multivitamin containing vitamin A, make sure it doesn’t go much above the RDA and that at least 25% of the vitamin A comes from beta carotene. Or simply supplement with beta-carotene by taking 5,000-25,000 IU Vitamin A activity per day with meals.
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