Bone Health in Highly Trained Female Athletes:
A Review of the Current State of Knowledge
By B- FIT
As featured in the Web Only issue of Running Times Magazine
Highly trained female athletes are often at peak cardiovascular fitness but face important threats to their skeletal health. Women that train intensively may produce abnormally low levels of estrogen, which in turn, may lead to weakened bones. Low bone strength (or osteopenia), is a risk factor for stress fractures. Young adults with osteopenia are also more likely to develop osteoporosis later in life. It is generally accepted that exercise promotes bone health. However, research focusing on the relationship between intensive exercise, bone health, and estrogen produce alarming results concerning the health of female athletes. The hormone estrogen is responsible for growth and development of reproductive organs, as well as onset and regulation of menstruation. In addition, estrogen is essential for maintaining bone health in women. Events that result in rapid declines in a woman’s estrogen level, such as menopause and ovariectomy (removal of the ovaries), also result in rapid losses in her bone mass and bone strength.
Regular vigorous exercise is associated with decreased estrogen levels in the blood. In one study, healthy women who began training for a marathon reduced their estrogen levels by over 50%. These low estrogen levels often result in menstrual irregularity in a large proportion of intensively training athletes. Irregularities can include a late onset of menstrual periods, infrequent periods (oligomenorrhea), absent periods (amenhorrea), or more subtle abnormalities, such as a shortened luteal phase and anovulatory cycles. (The luteal phase refers to the phase of menstruation during which progesterone is released from the ovum and the uterine lining proliferates; anovulatory cycles are those menstrual cycles in which a woman does not ovulate properly. These abnormalities can only be detected by specific medical tests.) A recent survey of competitive collegiate cross-country runners found that 56% missed several menstrual periods a year or had no periods at all. Cumulative incidence of amenorrhea (loss of period) and oligomenorrhea among all athletes is even higher. Most studies have considered athletes with infrequent or absent periods and have not evaluated athletes with more subtle menstrual disturbances. However, one study found that runners who menstruate monthly but who have anovulatory cycles and/or shortened luteal phases also lose bone. This study is of particular interest because it demonstrates that highly training females who appear to be menstruating normally may still be at risk for osteopenia.
The cause of estrogen-deficiency and menstrual irregularity in athletes is not known with certainty. However, studies have identified these risk factors: earlier onset of training, more intense training, psychological stress, nutritional inadequacy, low body weight, low body mass, and changes in body composition.