During winter when sunlight is scarce, it's not hard to become vitamin D deficient without a supplement. Vitamin D deficiency actually afflicts 30 percent to 50 percent of the population, and it can be serious: deficiency has been linked to poor muscle function and weaker bones, plus a greater likelihood of developing autoimmune diseases, some cancers, diabetes, heart disease, and depression. There is mounting evidence that enough vitamin D in our bodies reduces the risk of nearly every disease that afflicts humans. Read on for the lowdown on how this vital vitamin works in the body.
Bone health Vitamin D plays a larger role in protecting and building bones than calcium. In addition to stimulating the absorption of calcium in the gastrointestinal tract, we can count on vitamin D to enhance bone-building activity by osteoblastic (bone) cells.
Muscle function Vitamin D is responsible for calcium transport, which is an integral part of muscle contraction and relaxation. Research even shows that maintaining vitamin D sufficiency can help increase muscle mass. A study on ballet dancers published in the Journal of Science and Medicine in Sport found that dancers given a vitamin D supplement of 2,000 IU daily during the winter increased their strength and vertical jump height and reduced frequency of injury compared to a control group . A 2012 study published in the same journal on competitive runners in the United Kingdom found that those who took 5,000 IU of vitamin D daily for eight weeks had faster sprint times and fewer injuries.
Immune system It’s not surprising that vitamin D plays a role in the strength of the immune systems since vitamin D receptors are expressed in all tissues, including immune cells, the brain, skin, kidneys, and all glands. Cancer We have vitamin D receptors on every cell in our bodies, regulating multiple gene and cellular functions associated with breast cancer suppression. An analysis of more than 19 studies published in Breast Cancer Research Treatment Journal found that 75 percent of women with breast cancer have inadequate vitamin D levels, and that women with the highest vitamin D levels were 45 percent less likely to get breast cancer. Studies published in the American Journal of Clinical Nutrition and Anticancer Research found a strong positive relationship between sufficient vitamin D status and lower rates of prostate, pancreas, lung, and endometrial cancers.
Diabetes types 1 and 2 Studies have shown that younger people who have higher vitamin D levels are less likely to develop type 2 diabetes later in life compared to those with lower vitamin D levels. Studies have also shown that vitamin D supplements can alleviate some symptoms of type 2 diabetes. As for type 1 diabetes (often termed juvenile diabetes), Finnish studies of children beginning in the 1960s and following them over a period of 30 years showed that vitamin D may help prevent this type of diabetes. In children given 2,000 IU of vitamin D daily during the first year of life, risk of developing type 1 diabetes dropped by a whopping 78 percent. Children in this study who were vitamin D deficient and not receiving supplements had an almost 300 percent greater risk of developing type 1 diabetes.
So, how much vitamin D should you take? 2,000 IU each day is enough to meet the needs of most people who have limited sun exposure, so look for a supplement that contains at least this much. (Editor's note: for a vitamin D supplement free of animal ingredients, check out Deva Nutrition Products' vegan vitamin D supplements.)
- Talia Fuhrman has a B.A. in nutritional sciences from Cornell University.