Healthy bones for sports and life

Young female athletes are at risk of low bone density. Building strong bones can help prevent sports injuries now and osteoporosis later.

Most teenage girls don't spend much time thinking about their bones. The threat of osteoporosis — a disease that makes bones fragile and prone to break — just is not on their radar. But adolescence is a critical time for bone health, because maximum bone development takes place in the years between puberty and age 18.

For girls and young women who train hard at sports, the problem of weak bones isn't just in the future. Female athletes are more likely than are nonathletes to have low bone mineral density. Bone mineral density (BMD) refers to how much calcium and other minerals are in bones. A bone's strength depends on its size and density. The higher the bone mineral content, the denser and generally stronger the bone is.

About 16 to 22 percent of high school female athletes have low BMD, which increases the risk of having stress fractures or other bone-related injuries.

Invest early in the "bone bank"

Bone is living, growing tissue that is constantly changing. Throughout life, bits of old bone are broken down and removed, and new bone is formed, a process known as bone remodeling.

In young girls, the body makes new bone faster than it breaks down old bone. The skeleton grows in both size and density. Bone mass — the amount of bone tissue in the skeleton — increases rapidly. The most critical time for girls to build bones is between ages 10 and 16. By age 18, girls have reached 90 percent of their peak bone mass, while boys do so by age 20. Peak bone mass is the maximum amount of bone mass a person will achieve in life.

Most individuals reach peak bone mass by age 30. After that, bone remodeling continues, but slightly more bone mass is lost than is gained. Think of it as a bank account. The higher peak bone mass is, the more bone is "in the bank" to draw from later in life. This reduces the likelihood of developing osteoporosis.

For young female athletes, doing everything possible to bank bone also pays off in the present. Strong bones help prevent injuries to bones and to muscles.

The big deal about BMD

Low BMD is one of the three components of the "female athlete triad," along with consuming fewer calories than the body needs for its activity level (low energy availability) and menstrual cycle disturbances. And either of these other two conditions can also cause low BMD.

Teenage girls who don't menstruate or who have longer than normal times between periods produce less estrogen, the hormone that regulates the rate at which bone is broken down (bone resorption). If estrogen becomes chronically low, then bone resorption can occur at a faster rate than it should. The result? Less bone mass is accumulated, and BMD is lower.

But even female athletes who have regular menstrual periods can still have low BMD. The physical and emotional stress of intense training can cause changes in growth hormone and cortisol production that also negatively affect BMD. A diet that is low in calcium, vitamin D and other nutrients needed for bone formation can all result in lower BMD.

Jan. 06, 2017