BMI and Menstruation

Factors that often play a role in the regularity and flow of a woman’s menstrual cycle include hormone changes, genetics, serious medical conditions and body mass index. Of all these factors, you have the most control over your body mass index, or BMI. Having a high or low BMI may cause you to experience an absence of menstruation, irregular menstruation and painful menstruation. Aim to keep your BMI within the normal range to promote regular and healthy menstrual cycles.

Body Mass Index

Your BMI, calculated from your weight and height, provides a numeric indication of the amount of fat you carry on your body. Calculate your BMI by first finding the square of your height in inches. Divide your weight in pounds by the number representing the square of your height in inches. Finally, multiply your answer by 703. A normal BMI falls between 18.5 and 24.9. If you have a BMI under 18.5, you have underweight. You are classified as having overweight if you have a BMI between 25 and 29.9, and you are considered as having obesity if your BMI is greater than 30.

Obesity and Menstruation

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Obesity may cause you to have no period, referred to as amenorrhea; infrequent periods, referred to as oligomenorrhea; no ovulation, referred to as anovulation; and heavy or long periods, referred to as menorrhagia. A young girl with a BMI over 30 has an increased risk of experiencing early menarche, meaning she has her first period before the age of 12. If this occurs, she has an increased risk of developing heart disease or dying from cardiovascular disease, according to a study published in the December 2009 issue of “The Journal of Clinical Endocrinology and Metabolism.” If you have a high BMI, consider losing weight in a healthy manner. A balanced, reduced-calorie diet packed full of nutrient-dense produce and whole grains, which allows you to lose 1 to 2 lbs. a week, provides the safest weight-loss option.

Underweight and Menstruation

A low BMI often stops menstruation. A low BMI may result from excess physical training, lack of calorie intake or genetics. If you get your BMI back to normal levels, you may start experiencing normal menstruation. However, some women, especially those with anorexia nervosa, continue to experience amenorrhea -- even after returning to normal BMI levels.


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If you miss more than two periods or notice your period becoming very light, very heavy or irregular, consult your doctor. Absence of periods and infertility are associated with both high and low BMIs. Also seek medical advice if you experience painful periods. Any major change in your menstrual cycle may result from medical conditions such as thyroid or pituitary problems, certain medications, polycystic ovary syndrome or endometriosis.