Every day, thousands of women suffer from the uncertainty and aggravation of an irregular period. From the moment we have our first menstrual cycle until menopause arrives, we’re taught that a regular cycle is a critical indicator of our overall physical health. If your period comes at irregular intervals, it’s usually a sign that something is wrong.

Several underlying problems could impact your menstrual cycle. For example, prolonged stress or the use of birth control can disturb your period, as can more serious conditions afflicting the ovaries. However, one of the most common but overlooked reasons that your menstrual cycle arrives off-schedule is related to your thyroid.

Both hypothyroidism and hyperthyroidism can cause menstrual cycle irregularities. Here’s why.

What is the thyroid?

The thyroid is a butterfly-shaped gland located at the front of your neck. Its primary function is to secrete a hormone that affects a vast array of bodily functions. This hormone helps you stay warm and keeps your organs functioning as they should.

When your thyroid produces too much of this hormone, you might experience a condition called hyperthyroidism. When it makes too little hormone, you might have hypothyroidism.

If your thyroid is producing too much or too little thyroid hormone, you’ll begin to notice a variety of symptoms, including fatigue, dry skin, thinning hair, brain fog, increased feelings of cold and more.

Thyroid issues in women

Unfortunately, thyroid issues—especially hypothyroidism—are more common in women. What’s more, women can experience serious problems with their entire reproductive system as a result of these thyroid troubles.

In some cases, when a woman becomes pregnant, changes in her body chemistry can create the conditions that cause thyroid dysfunction. Other times, the body’s transformation after pregnancy can lead to thyroid problems. In even more cases, thyroid problems occur because of something else entirely.

Regardless of the underlying cause, one of the first signs of thyroid problems in women is irregularities in your menstrual cycle. Hyperthyroidism can lead to heavier-than-average flows, while hypothyroidism can result in extra-light flows and very irregular periods. It can also cause the absence of your menstrual cycle for months at a time.

But how, exactly, does the thyroid impact your menstrual cycle? There are actually a few ways this irregularity can occur.

The metabolism connection

Your thyroid plays a significant role in your body’s metabolism. You may not realize it, but your menstrual cycle is a key metabolic process.

The thyroid’s connection to your metabolic cycle means that when your thyroid begins pumping too much or too little thyroid hormone into your bloodstream, your body’s metabolism gets disturbed.

The prolactin problem

One of the byproducts of an under-active thyroid is a hormone known as prolactin. This little-discussed hormone is an integral part of what regulates immunity, blood cell formation, ovulation, the reproductive cycle and breast milk creation (which is the reason it’s often referred to as the “milk hormone”).

When your body is exposed to excessive amounts of prolactin, it can disrupt the production of other substances like estrogen and progesterone. When there is too much or too little of any of those substances, it can wreak havoc on your menstrual cycle.

Bleeding isn’t always a sign of health

You might think that if your period has arrived, you’re in good shape, but that might not be the case. In a typical menstrual cycle, the release of an egg during ovulation generates progesterone. In turn, progesterone regulates the menstrual cycle, the process by which your body ejects that unfertilized egg.

If hypothyroidism has caused an abundance of prolactin to flow through your system, it can hinder the production of progesterone. When that occurs, your egg might not release, and the lack of progesterone leads to an abundance of unfocused estrogen. This excess estrogen runs rampant, stimulating the thickening of your uterine lining and leading to heavy bleeding. This can resemble a period, but it’s not. It’s actually a condition known as anovulatory bleeding.

Thyroid problems can be treated

If you suspect that thyroid problems have interfered with your regular period, you should schedule an appointment with your doctor. A straightforward blood test is all it takes to confirm or deny your suspicions.

The good news is that most thyroid problems are treatable with lifestyle adjustments and help from a scientifically proven collection of minerals and supplements. Iodine is one of the most crucial of these nutrients. Behind iodine, you should consider supplementing your daily diet with vitamins A and D, selenium, zinc and iron.