The Link Between BMI and Menstruation

Aug 12, 2011
Estela Kennen

Your weight can affect your menstrual cycle. - Bandita

If your BMI is too low or too high, you are at risk for a host of health problems, including an irregular menstrual cycle.

Your body mass index, or BMI, is a number based on your height and weight. While BMI does not directly measure fat, it is an often used and a reliable screen for the amount of body fat someone has.

A healthy BMI for adults is between 18.5 and 24.9. Adults with a BMI below 18.5 are considered underweight and those with a BMI above 30 are considered obese.

Normal Menstruation

When it comes to periods, there is a wide variation in what is considered “normal”. While menstrual cycles average 28 days, Dr. Elizabeth McLemore, an Obstetrician/Gynecologist at the Virginia Commonwealth University Health System, explains that it is normal for cycles to last between 24 to 35 days. The period itself typically lasts between four and seven days. But, Dr. McLemore adds that “Any female regardless of weight may experience irregular periods the first 5-7 years after the beginning of menstruation.”

Menstruation can also come with a lot of unpleasant side effects for even the healthiest woman. You may experience any combination of cramping, bloating, breast tenderness, moodiness, headaches and increased appetite the week before and during her period -- or none of these symptoms at all. Hormonal birth control, such as birth control pills, can also affect your menstrual pattern.

High BMI and Menstruation

Women with high BMIs can have longer than normal menstrual cycles. Another risk is PCOS or polycystic ovarian syndrome, adds Dr. Dana Redick, Assistant Professor of Clinical Obstetrics and Gynecology at the University of Virginia. Women with PCOS typically also have acne, facial hair, or other signs of high levels of androgen.

“This disorder is associated with skipping cycles,” explains Dr. Redick, “and if untreated can be associated with infertility, metabolic syndrome, diabetes, and even abnormal changes in the uterine lining.”

Low BMI and Menstruation

“Women with low BMI and especially those women who exercise vigorously (marathon runners, competitive swimmers, etc) or who suffer from eating disorders - may skip or even stop having cycles,” says Dr. Redick. This is because something has derailed the normal hormonal messages between the women’s brain and ovaries. Dr. Redick explains that female athletes are at risk for not only having missed cycles, but also thin bones (osteoporosis) and low energy.

Diagnosing the Problem

BMI is quick and easy to measure, so doctors often use it as as a screening tool. However, a change in BMI does not directly cause menstrual problems. Instead, there might be one or more underlying issues that caused both the BMI and the menstrual change.

“We evaluate [any woman undergoing significant unintentional weight changes] for underlying causes such as thyroid, pituitary, or adrenal gland problems,” explains Dr. Redick. “Some medications can affect appetite and/or weight so part of the evaluation is reviewing a patient’s medications.

Remember, too, that even women with normal BMIs can have menstrual problems. If you have any concerns, please talk to your doctor.