close up photograph of a womans thyroid

Heavy periods? Consider your thyroid

Heavy menstrual bleeding can affect up to 1 in 4 women (1). It’s defined as blood loss of greater than 80 mL or lasting longer than eight days (2). To visualize this, 80 mL equates to 16 fully soaked regular tampons, or eight fully soaked super-tampons over all the days of your period, or repeatedly soaking through a pad or tampon every two hours.

If you experience heavy menstrual bleeding, please see your healthcare provider. They will likely conduct investigations to determine the cause of your heavy bleeding. Possible causes include adenomyosis, fibroids, coagulation disorders, and “unopposed estrogen,” which means a hormone imbalance of too much estrogen and not enough progesterone (3).

Tip: Progesterone thins the uterine lining and prevents heavy menstrual flow (3).

Another possible cause of heavy periods is hypothyroidism, or underactive thyroid (4, 5).

Tip: The thyroid gland is located in the front of the throat and makes thyroid hormone, which regulates metabolism. When the thyroid is underactive, it cannot make sufficient thyroid hormone.

How can an underactive thyroid cause heavy periods?

There are several mechanisms by which an underactive thyroid can make periods heavier:

  • Without sufficient thyroid hormone, your ovaries may not be able to make enough of the flow-decreasing hormone progesterone (6).
  • Without sufficient thyroid hormone, you may not make enough of the coagulation factors you need to prevent heavy bleeding (7, 8).
  • Without sufficient thyroid hormone, you make less of the estrogen-binding protein SHBG and so are exposed to more estrogen (3, 7).

If your healthcare provider discovers that you have an underactive thyroid, then your best treatment for heavy periods may be to take thyroid hormone (9).

Lara Briden is a naturopathic doctor with 20 years of experience in women’s health. Her book is Period Repair Manual: Natural Treatment for Better Hormones and Better Periods. Follow her on Twitter and Instagram.

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