Hypothyroidism In Women With PCOS: Is There A Connection?

Polycystic ovary syndrome (PCOS) is a common endocrine disorder that affects people assigned female at birth (AFAB). Hypothyroidism, sometimes known as underactive thyroid is also more common in people with ovaries. Understanding the possible connection between the two conditions and how to manage them is important for your quality of life and your fertility. Here’s what the current science indicates.

What is the connection between PCOS and hypothyroidism?

PCOS is characterized by elevated androgens, insulin resistance, small cysts on the ovaries, and reduced fertility. Hypothyroidism happens when your thyroid isn’t producing enough hormones or when your body doesn’t recognize it and keeps releasing a pre-hormone (TSH) to produce more thyroid hormones.

Studies show a significantly higher prevalence of thyroid disorders, especially Hashimoto's thyroiditis (HT), in people with PCOS, but the mechanism of association hasn’t been established. As both diseases are known to be partially genetic, there may be common genes participating in their development, one of which is the FBN3 gene.¹

Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis, is an autoimmune disorder that causes inflammation of the thyroid, impairing the thyroid's ability to produce thyroid hormones. In the United States, it’s the most common cause of hypothyroidism. The disorder is typically diagnosed with symptoms of hypothyroidism and, often but not always, an enlarged thyroid gland (goiter).

Can PCOS and hypothyroidism be confused?

There’s some symptom overlap between PCOS and hypothyroidism. Specifically, both conditions can cause fatigue, weight gain, depression, and irregular or heavy menses. Because of this, it’s possible to misdiagnose them, particularly in middle-aged cisgender women (the group most often impacted by Hashimoto's thyroiditis).

Both conditions can affect the reproductive cycle and reduce fertility. Many people with PCOS are diagnosed younger, although some go undiagnosed until they attempt to have children.

Low levels of thyroid hormones can cause anovulatory cycles, luteal phase defects (badly developed follicles), and sex hormone imbalances. 

Luteal phase defects can cause polycystic ovaries, similar to the appearance of ovaries affected by PCOS. Because of this, many doctors check thyroid levels when investigating infertility, especially as the diagnosis can be made with a cheap blood test and treatment is an inexpensive oral medication.

Diagnosing PCOS and hypothyroidism

PCOS is often a diagnosis of exclusion, as other disorders can present similar symptoms. If you have symptoms of PCOS, such as hirsutism, irregular periods, and acne, your doctor will take samples to check your androgen and blood sugar levels. Hypothyroidism, as mentioned, is diagnosed with a simple test to look at levels of thyroid hormones in your blood.

Because PCOS is a diagnosis of exclusion, it’s not uncommon to check thyroid levels first and, if they’re out of balance, treat for hypothyroidism. This means that PCOS can sometimes be missed in people with hypothyroidism. If you have signs of elevated androgens, such as irregular menstrual periods and excess hair growth, you may consider asking your doctor to check for both conditions. 

Hypothyroidism cannot become PCOS, but there are indications that PCOS can lead to hypothyroidism. By causing elevated estrogen, PCOS can further increase the risk of developing hypothyroidism and autoimmune diseases in general.

Treating PCOS and hypothyroidism

The standard treatment for hypothyroidism is oral therapy with levothyroxine. Levothyroxine is typically taken as a single pill every day in the morning, with the dosage adjusted to keep thyroid hormones in balance. In some cases of infertility, levothyroxine therapy started at least three months before pregnancy is sufficient to allow conception. Hypothyroidism is thus much easier to manage than PCOS. One sign that you may have both is if levothyroxine therapy does not resolve your symptoms.

PCOS is typically treated with oral contraceptives if you aren’t currently trying to get pregnant. If you are attempting to conceive, the front-line treatment is metformin, a drug more normally used to treat diabetes and prediabetes. Metformin is an insulin sensitizer that reduces the insulin resistance associated with PCOS.

However, patients taking both drugs often show lower TSH (thyroid stimulating hormone) concentration. This isn’t caused by a direct interaction between the two medications and doesn’t affect other thyroid hormone levels. It appears that metformin may affect thyroxine receptors and enhance thyroxine bioavailability. This means that if you’re taking levothyroxine and start taking metformin, your levothyroxine dosage will likely need to be adjusted.

Levothyroxine shouldn’t be taken within four hours of calcium or fiber supplements, and you should avoid coffee immediately after taking the medication. But there’s no indication that you need to separate when you take metformin from when you take levothyroxine. However, levothyroxine should be taken on an empty stomach (typically 30-60 minutes before breakfast), while metformin is best taken with food to reduce potential gastric disturbances.²

Effects of PCOS and hypothyroidism on pregnancy

Both conditions can negatively impact your ability to conceive, and both should be treated if you’re attempting to become pregnant.

Levothyroxine is safe for use during pregnancy. In fact, it’s best to increase your dose as soon as pregnancy is confirmed and get frequent blood tests. Low levels of thyroid hormone are associated with pregnancy loss. If your thyroid is normal, it naturally increases production to provide for your baby's needs, but an impaired thyroid is not able to do so. 

Continue to check your dosage while breastfeeding since low thyroid hormones can reduce your milk supply. Levothyroxine won’t harm your baby, and while small levels will be secreted in breast milk, it’s normal for breast milk to contain thyroid hormones. You’ll need to stay on the elevated dosage if breastfeeding.

Metformin is safe during pregnancy and can improve your chances of conception. It also reduces your risk of pre-eclampsia. However, metformin can cause gastrointestinal side effects and thus could potentially worsen morning sickness. This actually seems to be less common if you have PCOS. It’s safe to continue to take metformin while breastfeeding, and, in fact, it may slightly increase your milk production.

If untreated, however, both conditions can increase your risk of pregnancy loss. It’s very important that you talk to your doctor as soon as you decide to attempt to become pregnant and continue to take your medication throughout. With levothyroxine, it’s important to switch to the higher dose as recommended and not switch back without talking to your doctor. You’ll most likely need to take a higher dose until your child is weaned.

Lifestyle changes to help control PCOS and hypothyroidism

The most important thing you can do if you have one or both of these conditions is to eat a healthy diet. It's a good idea to talk to a nutritionist, especially if you’re trying to get pregnant. Make sure to get the full list of foods you shouldn’t eat too close to the time you take your thyroid medication.

It’s also important to try to get enough sleep. Practice good sleep hygiene, such as keeping your bedroom slightly cool, not doing anything in bed other than sleeping and sex, and avoiding electronic use late at night.

Exercise can also help with symptoms of both and ease symptoms of depression. Try 30 minutes of moderate-intensity exercise at least five days a week. Choose activities you enjoy and will be able to keep up with.

The lowdown

There may be a connection between PCOS and hypothyroidism. Specifically, PCOS appears to be associated with autoimmune diseases in general, and this includes the most common form of hypothyroidism, Hashimoto's thyroiditis.

Both conditions can have similar symptoms, including the existence of multiple small cysts on the ovaries, and both can impact fertility. Because hypothyroidism must be ruled out before making a PCOS diagnosis, some cases may be missed because they coexist with hypothyroidism. If your symptoms don’t improve with medication, talk to your doctor about the possibility of having both.

Often, hypothyroidism is relatively easy to manage with oral medication. Having a doctor identify and treat both hypothyroidism and PCOS can help you feel your best and improve your reproductive health.