Nutritionists have long known that vitamin D and calcium work together to build and repair strong bones. Both nutrients also affect the muscles and their movement, and vitamin D receptors have recently been discovered in muscle tissue. Because of their roles in supporting skeletal and muscular health, calcium and vitamin D may help improve athletic performance.
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Calcium and Vitamin D in the Body
Calcium is probably best known for its role in building and maintaining healthy bones, but it also contributes to nervous system and muscular functioning, circulation, and the release of hormones in the body. Vitamin D supports the absorption of calcium in the digestive system, and regulates the levels of calcium and other minerals in the body. Deficiency in calcium or vitamin D may lead to a greater incidence of stress fractures in athletes. In addition, a 2010 review published in the “Scandinavian Journal of Medicine & Science in Sports” noted that vitamin D plays a role in muscle structure and function, and that vitamin D deficiency may result in decreased muscle performance.
Calcium and Vitamin D Sources
Dairy products are rich in naturally occurring calcium, and dark greens like kale and broccoli are also excellent sources. In addition, many foods are fortified with calcium, including breakfast cereals, tofu and fruit juices. According to the National Institutes of Health, it is difficult for most people to get enough vitamin D from naturally occurring food sources such as fatty fish and fish oils. Most of the vitamin D in the American diet comes from fortified foods, including milk, fruit juices and breakfast cereal. In addition to food sources, the body can produce its own vitamin D when the skin is exposed to the ultraviolet radiation in sunlight.
Effectiveness of Calcium and Vitamin D Post-workout
Scientific research on the effect of calcium and vitamin D in post-workout nutrition is scarce. A study published in “Medicine & Science in Sports & Exercise” in 2010 found that women who drank fat-free milk after working out became stronger, gained more lean muscle mass and lost more body fat than women who drank a carbohydrate drink after their workouts. Because milk is high in calcium and vitamin D, these results are encouraging for supporters of the theory that post-workout calcium and vitamin D consumption increase athletic performance. It is unclear, though, whether the same results could be achieved with supplements or other dietary sources of the nutrients, or whether the protein content of the milk was responsible for the differences between the groups.
Both calcium and vitamin D can cause adverse effects if consumed in excess. Vitamin D toxicity can cause a range of non-specific symptoms, such as heart arrhythmia and weight loss. Because of its role in calcium absorption, vitamin D can also cause calcium levels to rise in the blood. Too much calcium can cause constipation, may affect the body's ability to absorb iron and zinc, and may cause kidney stones. Vitamin D or calcium supplements may also interact with some medications. Tell your doctor if you are taking any dietary supplements to avoid negative interactions.