The female athlete triad. No, we’re not talking Serena Williams, Danica Patrick, and Annika Sorenstam here. This triad refers to an interconnected series of health issues that can plague young female athletes, one of which is osteoporosis.

Osteoporosis? At age 16? Sadly, even high school girls can develop osteoporosis. And their risk factors aren’t smoking, a sedentary lifestyle, or alcohol abuse, as they are with older women. Far from it. Osteoporosis in young women can be the result of fitness taken to an extreme: the female athlete triad.  

The three parts of this little-known yet devastating syndrome are energy deficiency, caused by too much exercise and too little nourishment; amenorrhea, when a young woman who’s started menstruating stops for longer than 3 months; and osteoporosis, caused by lack of calcium and estrogen. A girl can have one, two, or all three of these conditions. Let’s look at each alone, then consider how they can come together to destroy a seemingly super-fit young woman’s health.

• Energy deficiency: Many teenage girls diet. OK, let’s say it’s the rare one who doesn’t. But not many diet to the extreme, while also carrying on a regimen of intense physical training—training for a sport that may also place value on a lithe, svelte body, like figure skating or gymnastics. Or a sport that classifies girls by weight, like martial arts or rowing.

You’ve heard the expression calories in, calories out? Our bodies need a certain number of calories, provided by what we eat, to function normally. If you burn more calories than you take in, you lose weight. If you burn WAY more calories than you take in—by severely limiting the types and quantity of the foods you eat, and/or by exercising for hours every day—then you exhibit energy deficiency.

Anorexia and bulimia are examples of energy deficiency that are based on lack of calories, rather than too much exercise. But the effect is the same: painful thinness. And this condition leads to the second part of the triad:

• Amenorrhea: Losing too much weight causes a woman’s body to lower its estrogen production. This in turn can wreak havoc with the menstrual cycle, making periods irregular, or stopping them completely. (Some female athletes like swimmers and gymnasts, who start intense training at a very young age, may never even start menstruating until they lessen the intensity of their workouts.)

When a young woman who’s had regular periods stops having them for longer than three months, she has amenorrhea. And this helps lead to the third condition of the female athlete triad:

• Osteoporosis. Extreme thinness. Lack of calcium due to a severely restricted diet. Lack of estrogen. Sounds familiar, right? We’re talking major risk factors for osteoporosis in older women. Well, those same risk factors apply to younger women as well. Only it’s not menopause or failure to take vitamin D supplements that’s at the base of these risk factors. It’s exercise and lack of food, pure and simple.