Are you getting enough calcium?

A study published recently in the Journal of Bone and Mineral Research suggests that some athletes may be at risk of bone loss. We often think of exercise as being good for bones. Under most circumstances, exercise helps improve bone density and reduces the risk of osteoporosis. This is particularly so for weight-bearing activities such as running and weight lifting. However, during prolonged exercise, especially in the heat, a large amount of calcium can be lost through sweating. It is possible that athletes who engage frequently in prolonged vigorous exercise are at risk of losing bone. This is because bone acts like a reservoir for calcium and in fact, 99% of calcium in the body is found in bone. When fluid levels of calcium drop due to sweating, bone must offer up some of its calcium to help maintain homeostasis. Under such conditions, it seems it is more important for the body to maintain fluid levels of calcium than it is to maintain bone calcium. Calcium is important for cell function, nerve conduction and muscle contraction.

Drs Daniel Barry and Wendy Kohrt from the University of Colorado in Denver studied 14 male competitive road cyclists over a 1-yr period to determine whether or not bone loss occurred in these athletes. The investigators measured calcium loss through sweating during several cycling sessions and they measured bone density before and after the 12-month period. Here is what they found:

Bone mineral density decreased in the hip bones over a 9-mon competitive season with some recovery during a 3-mon post-competitive season.

Calcium loss during 2 hrs of cycling was estimated to be 135 mg.

Calcium loss was associated with bone mineral density. The greater the loss, the lower the density.

What does this mean to paddlers? Paddling, like cycling, is a weight-supported activity. In contrast, running is a weight-bearing activity. Athletes who engage primarily in weight-supported activities such as cycling, paddling or swimming may be at greater risk of bone loss than those athletes who engage in weight-bearing activities. In addition, paddlers who sweat heavily over prolonged periods are at an even greater risk. Despite sweating less, women can also be at risk because they generally have lower bone mineral content than men. Calcium supplementation may be necessary and it is possible that the RDA for calcium is inadequate for long distance paddlers.

My advice to you is to bone up on the types of supplements and calcium-rich foods that are out there and make sure you are getting adequate amounts. A good source of information on calcium can be found at the National Institute of Health's Office of Dietary Supplements website: http://ods.od.nih.gov/factsheets/calcium.asp

Reference:
Barry D. & W. Kohrt. BMD decreases over the course of a year in competitive male cyclists. J. Bone Mineral Res. Vol23, 2008.