According to a new US study, taking combined calcium and vitamin D supplements before exercise may be an important factor for the skeleton to adapt to physical activity.
In the clinical study, 52 men age 18 to 45were randomly assigned to take 1,000 milligrams of calcium and 1,000 international units of vitamin D either 30 minutes before or one hour after exercise (1). The exercise comprised a simulated 35-kilometer time trial, and participants wore skin patches to absorb sweat. Blood levels of calcium and parathyroid hormone as well as body weight (adjusted for fluid intake) were measured 30 minutes before and 1 hour after exercise. In addition, the amount of calcium in the sweat from the skin patches was measured to estimate the calcium lost through the skin during exercise. The study results showed that the exercise-induced decrease in blood calcium occurred whether the supplements were taken before or after exercising. Pre-exercise supplementation, however, resulted in less of a decrease. Although not statistically significant, parathyroid hormone levels increased slightly less among cyclists who took calcium before exercising.
The researchers commented that these findings are relevant for individuals who engage in vigorous exercise and may lose a substantial amount of calcium through sweating. Taking calcium before exercise may help keep blood levels more stable during exercise, compared to taking the supplement afterwards, but the long-term effect of this on bone density is not yet known.
Previous research has shown that a year of intense training is associated with substantial decreases in bone mineral density among competitive road cyclists (2). Experts believe that this kind of exercise-induced bone loss could be related to the loss of calcium during exercise. As blood calcium levels drop, the parathyroid gland produces excess parathyroid hormone, which can mobilize calcium from the skeleton, weakening bones.