While most vitamins, like A, the B’s, C and E, are essential, vitamin D is technically nonessential. That’s because the skin produces vitamin D upon exposure to light. Despite this, it is still essential that you supplement with vitamin D. That is, if you want to reap all its benefits, which include better bone building, fewer colds, higher testosterone levels, more strength, better mood and brain function, and even greater fat loss.
There are two forms of vitamin D: D-3 (cholecalciferol) and D-2 (ergocalciferol). Vitamin D-2 is found in plant sources and some supplements and can only enter the body through the diet. As mentioned above, sunshine triggers vitamin D production in the skin by converting cholesterol into vitamin D-3. That form can also be acquired through the consumption of animal products like fatty fish or by supplementation. However, both those forms are inert and must be converted to the active form of the vitamin, a steroid hormone called 1,25-dihydroxyvitamin D, before the body can use it. That work is done by the liver and the kidneys, and because D-3 is more readily converted to the active form, it’s considered the more potent form of the vitamin. Any extra D that’s not immediately needed by the body is stored in fat tissue for future use.
Although in theory, the body should be able to make all the vitamin D it needs, in reality, it doesn’t even come close, regardless of how much sun time you get. Supplementing with vitamin D is, therefore, essential.
The D You Know
Some of vitamin D’s functions have been so well-publicized that you likely don’t need us to tell you about them. The most obvious is its role in promoting bone health. Vitamin D helps to maintain bone health by aiding calcium absorption and regulating the movement of calcium in and out of bone tissue. Without D, you would absorb less than half the calcium you do from food and supplements. (This is why dairy products are almost always fortified with D.) Vitamin D also bolsters the immune system, triggering the killer T cells that fight off germs like colds and flu before they can beat you down and force you to miss workouts.
Vitamin D also may help to protect from certain cancers. One study in the American Journal of Preventive Medicine reported that women living in sunnier regions of the world had higher blood levels of vitamin D, as well as a significantly lower risk of ovarian cancer, than those in less sunny regions. Another study found that sun exposure and a diet rich in vitamin D lowered the risk of breast cancer. And sunshine exposure also has been correlated with a lower risk of colon cancer.
You may know that vitamin D boasts brain benefits. Low levels of vitamin D are associated with psychiatric and neurological disorders, as well as a greater cognitive decline with aging. One study from the Washington University School of Medicine in St. Louis reported that vitamin D deficiency was associated with depression and diminishing cognitive performance. In fact, Georgia State University researchers reported that individuals with vitamin D deficiency have an 85 percent greater risk of developing depression.
The D You Don’t Know
In addition to the many health benefits covered above, vitamin D has several physique and performance benefits that are worth noting. Given that vitamin D gets converted into a steroid hormone in the body, it makes sense that it has effects on muscle fibers. The active form of D binds to specific receptors found on muscle cell membranes and in muscle cell nuclei. When it binds to these receptors, it enhances muscle contraction and protein synthesis — the buildup of muscle protein. Research shows that certain types of these receptors may be responsible for greater muscle size and strength. Although you can’t alter the type of vitamin D receptors you have in your muscles, making sure you have adequate levels of D in your body can help ensure your receptors are activated for optimal muscle function, strength and growth.
Another study reported that female students at the University of Southern California who had lower blood levels of vitamin D had significantly higher levels of fat in their muscles than those with high blood levels of vitamin D. (Yes, the body can store fat in muscles as well as under the skin.) Having fattier muscles not only means that you have more total body fat, but it also can result in weaker muscles with less endurance. Muscles with higher fat content have impaired mitochondrial function, so they produce less energy and can develop reduced insulin sensitivity.
Although researchers are not sure precisely how vitamin D prevents fat accumulation in muscle, it is well-known that vitamin D and calcium work together to encourage fat loss. One recent study published in the journal Clinical Nutrition reported that when men and women consumed a breakfast containing more than 500 milligrams of calcium and about 350 IU of vitamin D, they burned more calories and fat and ate 320 fewer calories throughout the day as compared to when they started the day with a breakfast containing about half as much calcium and D.
Because vitamin D is produced in the body from cholesterol, as is testosterone, it follows that higher vitamin D levels can encourage higher testosterone levels in men. In fact, Austrian scientists from the Medical University of Graz reported that men with higher blood levels of vitamin D had significantly higher levels of testosterone and lower levels of sex hormone-binding globulin than those with low levels of vitamin D in their blood. Having lower SHBG means that more of the testosterone produced is free to get into muscles and increase muscle growth. This group of researchers did a follow-up study on men to see whether vitamin D supplementation actually could raise testosterone levels. They reported in a recent issue of Hormone and Metabolic Research that the men receiving just more than 3,300 IU per day of vitamin D for one year had a 25 percent increase in testosterone levels, while those getting a placebo had no such rise.
So how much vitamin D do you have to take to increase bone health, promote better immune function, enhance mood and brain function, boost testosterone levels, increase muscle size and strength, and encourage fat loss? Although the Recommended Daily Allowance is 200 IU per day, many scientists and doctors are recommending that you get at least 10 times that amount per day. We suggest you go with 2,000 to 5,000 IU per day, taken with meals, to maximize all of D’s benefits.
But while it’s not important that you supplement with a particular brand of vitamin D, it is important that you supplement with D-3. One study from Creighton University reported that D-3 supplements were 90 percent more potent at raising levels of 25-hydroxyvitamin D, the storage form of vitamin D in the body, than vitamin D-2. It also increased stored levels of the vitamin three times more than D-2 did.