Can a low body fat percentage of 17.5% cause irregular periods?

Doctor's Answers 1

If a teenage girl does not get her period by the age of 16, she has primary amenorrhea (or absence of menses), which is typically caused by structural or chromosomal abnormalities or functional problems with the hypothalamus or pituitary gland. But when a woman who’s previously had her period stops menstruating for three months or longer, and she’s not pregnant or in menopause, it is called secondary amenorrhea. While secondary amenorrhea can have many causes, it’s important for a woman to find out why her periods have stopped.

Ovulation is a vital sign of general good health. Almost every organ in the body can disrupt the cascade that initiates and sustains normal menstrual cycles. It’s not normal for a woman to not have periods. Amenorrhea can lead to bone loss, including osteoporosis and infertility.

Causes of irregular periods

The most common cause of irregular periods in young women is polycystic ovary syndrome. Other causes of secondary amenorrhea, assuming the woman is not pregnant or going through menopause, are anorexia and excessive exercise.

Changes in body weight can change menstruation patterns. Extremes of body mass index are associated with changes in menstrual cycle patterns and fertility patterns. A minimum proportion of body weight is needed to initiate menstrual cycles and maintain them. Thus, women who lose too much weight or are underweight can have changes in menstruation including but not limited to cessation of menstruation or prolonged periods of amenorrhea. Low body weight may be the cause of amenorrhea (the absence of periods for at least three consecutive months) for some people. There’s evidence to suggest that substantially low body weight (specifically, ten percent or more under typical weight) can affect the body’s hormonal functions, and potentially stop ovulation.

Excessive physical activity or stress, specifically, rigorous activities that burn a lot of energy can interrupt a person’s menstrual cycle. Likewise, immense stress may temporarily inhibit the functioning of the hypothalamus — the part of the brain responsible for metabolic processes; subsequently, a person’s ability to ovulate and menstruate may be affected.

Female athletes, especially young women, are more likely to have amenorrhea. Exercise itself does not cause amenorrhea. But it is more likely in women who exercise very intensely or who increase the intensity of their exercise rapidly. The combination of low body weight and intense exercise causes amenorrhea if the body believes it is in a “starvation state.” When the amount of energy expended during exercise is not balanced by adequate nutritional intake, the body begins to shut down organ systems that are not absolutely essential for survival.

Amenorrhea triggered by anorexia is usually a temporary condition. If a girl’s periods have stopped and the likely cause is anorexia, they should resume once she gains weight. Eating disorders may induce different menstrual patterns, but after a patient starts to be consistent with nutrition and is at a healthy weight, periods usually return within 6 months.

Further explanation of the causes

A woman who has a very low body weight will need to increase her body weight. Treatment for anorexia may require inpatient care at a specialized facility which includes intensive therapy, nutrition education and medical care.

Losing weight may result in periods stopping. This can occur if your body mass index (BMI) goes below 19. If you have an eating disorder called anorexia nervosa, losing too much weight can result in your periods stopping. It may also happen to athletes, gymnasts, long-distance runners and people who do an excessive amount of exercise.

Even among female athletes that train hard and eat plenty, amenorrhea is common. The biological explanation for this lies in the release of “stress hormones” that are part of the body’s normal response to exercise. These “stress hormones” interfere with the brain’s production of the reproductive hormones necessary to keep the menstrual cycle flowing.

Because of the altered production of reproductive hormones, women with exercise-induced amenorrhea are estrogen-deficient. Estrogen is one of the most important female hormones, and when there is too little of it, the health risks include infertility, atrophy of the vagina and breast, and osteoporosis (which can lead to fractures of the spine, hip, and other areas). Prolonged exercise-induced amenorrhea may also increase the risk of heart attacks later in life.

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