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Underweight and Amenorrhea

By Elizabeth Wolfenden ; Updated July 18, 2017

Amenorrhea is when a woman of childbearing age fails to menstruate. This condition affects 2 to 5 percent of all women of childbearing age in the U.S., according to Aetna IntelihHealth website. One of the things that may trigger amenorrhea is being underweight. If you have concerns about your weight or amenorrhea, discuss it with your doctor.

Primary Amenorrhea

Primary amenorrhea occurs when a girl has not had her first period by the time she is 15 years old. Girls with primary amenorrhea typically go through other changes of puberty but just do not start menstruating when expected. Primary amenorrhea is typically caused by abnormal chromosomes, vaginal obstruction, pituitary disease or problems with the hypothalamus. Although it generally not caused by being underweight, anorexia and too much exercise may also trigger this condition.

Secondary Amenorrhea

Secondary amenorrhea occurs when a woman who was menstruating suddenly stops menstruating for three months or more. Secondary amenorrhea can occur from having an extremely low body weight, but it also may be caused by a number of other factors. Pregnancy, stress, birth control medications, thyroid problems, strenuous exercise and certain types of medications may cause secondary amenorrhea.

Healthy BMI

You may be able to prevent some cases of amenorrhea by maintaining a healthy weight, determined by body mass index. To calculate your BMI, multiply your height in inches by your height in inches. Use that number to divide the number of your weight in pounds, then multiply that number by 703. If you don’t want to do the math yourself, use one of the many online BMI calculators. Women who have a BMI lower than 18.5 are underweight. Those with a BMI between 18.5 and 24.9 are at a normal weight, while those with a BMI between 25 to 29.9 are overweight. Women with a BMI of 30 or above are obese.


Aim to keep your BMI in the healthy range by eating a healthy and balanced diet. Make sure you are meeting the recommended daily value amounts for each nutrient. Aim for a moderate amount of exercise, but avoid exercising excessively. If you are having difficulty maintaining an appropriate BMI, contact your doctor for advice.

Risks of Being Underweight

In addition to increasing the risk of amenorrhea, there are a number of other concerns associated with being underweight, according to the August 2008 issue of "Today’s Dietitian." Underweight individuals may consume too few nutrients, which may lead to a weakened immune system and an increased risk of infections. They may have lower muscle mass, disrupted hormone regulation and hair loss. Underweight women also have an increased risk of osteoporosis and anemia.


Always seek your doctor’s advice if you have missed periods. Although some cases of amenorrhea may be triggered by being underweight, you should always get a full evaluation to determine if this is really what is causing your lack of menstruation. Do not attempt to diagnose the cause or treat this condition yourself.

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