Healthy Bones: What do endurance athletes need to know?

author : AMSSM

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If a training program increases in intensity too quickly, or does not include enough time for recovery, injury can result.

Our bones are in a constant state of remodeling, with osteoclasts breaking down bone and osteoblasts building it back up. This process allows for repair of microdamage, allows the bone to adjust to forces placed on it, and releases calcium from our bones (where it is stored) out to the rest of our body for use. Like muscle, bone will respond to weight-bearing exercise and become stronger by building itself up. However, if a training program increases in intensity too quickly, or does not include enough time for recovery, injury can result.

Stress fractures are thought to develop when the constant stress of training causes tiny microfractures in the bone, thus setting off the remodeling cascade. This starts with the osteoclasts breaking down bone, followed later by the osteoblasts that build it back up. If there is not enough recovery time, the osteoclast activity will surpass the osteoblast activity and a stress fracture will develop.

Nutrition is another factor important to bone health. The most important nutrition component is taking in enough calories for the level of activity that you are doing. Poor nutrition can affect bone health directly, by not giving your body what it needs to recover and restore what was lost; but it can also have an indirect effect, adversely affecting the hormonal levels that are important to your bones. Calcium is important for bone health, and getting 1500mg each day is the goal. Our bodies can only effectively absorb about 500mg at a time, so 500mg 3 times daily is recommended. Vitamin D assists in the uptake of calcium, and 800 IU is recommended. The research on bone nutrition is by no means complete, and there are other vitamins and minerals that seem to play a part, but we do not know enough to make any solid recommendations at this point other than to eat a healthy well balanced diet or take a daily multi-vitamin with minerals.

Hormones play a part in bone health for women. The small studies that have been done in men have shown that bone mineral density does not seem to be affected by low testosterone levels, unless the levels are so low that the hypogonadism is causing other issues as well. In women, however, estrogen is important for maintaining normal bone mineral density. Women can have low estrogen for a number of reasons. The most common reason is menopause, when we worry about women developing osteoporosis from the rapid decrease in bone density that accompanies the loss of estrogen. Low levels of estrogen also occur in younger women who are not having normal menstrual cycles, which is a risk factor in endurance athletes. Having menstrual periods start at a later age and skipping periods during intense training reduces the amount of estrogen and places women at risk of having decreased bone density. It is thought that endurance athletes who are missing periods are doing it because of an energy deficit, and it has been shown that increased caloric intake, and/or scaling back the level of training allows normal periods to return, indicating a return to a normal energy level and normal hormonal levels.

As you can see, bone health requires careful attention to training, nutrition, and overall health. In women, estrogen levels also play an important role. For further details and for treatment specific to your body, see your sports medicine physician.

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date: July 17, 2005