The Potential Link Between PCOS and Hypothyroidism

When investigating the cause of missed or absent periods accompanied by weight gain and/or abnormal hair growth or loss, doctors will consider two diseases associated with hormonal irregularities: polycystic ovary syndrome (PCOS) and Hashimoto's thyroiditis, which is the most common cause of hypothyroidism. Despite their unique biologies, these two conditions share features that suggest a potential link exists between them, albeit one that is complex and not fully sorted out yet.

Irregular menstrual periods are a hallmark feature of PCOS and occur as a result of increased androgen (male hormone) levels, which prevent regular, monthly ovulation (egg release). Besides irregular menstrual cycles, other potential symptoms of PCOS include excessive facial hair growth, hair thinning, and/or acne.

Hashimoto's thyroiditis is the most common cause of hypothyroidism and occurs when your immune system attacks your thyroid tissue. This misguided attack on the thyroid gland impairs the production of thyroid hormone causing symptoms like fatigue, weight gain, hair loss, and irregular menstrual cycles.

Perhaps the most notable shared feature between PCOS and Hashimoto's thyroiditis is the presence of polycystic ovaries. The term "polycystic" refers to the presence of multiple fluid-filled sacs (cysts) within each ovary. These cysts are actually ovarian follicles that are unable to mature enough to release egg cells.

In PCOS, the follicles cannot grow and mature properly due to high androgen levels. In hypothyroidism, hormone changes (specifically, a rise in the level of a hormone called prolactin) prevent ovulation, leading to polycystic ovaries.

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are two hormones released by the pituitary gland—a pea-sized gland located at the base of your brain. These hormones work to regulate your menstrual cycle.

In women with PCOS, the LH-FSH ratio is higher than in women without PCOS. Likewise, research has found that the LH-FSH ratio is higher in people with Hashimoto's thyroiditis.

Thyroid-stimulating hormone (TSH) is higher in people with a high body mass index (BMI). While experts have not fully teased out this association—it may involve the complex workings of inflammatory markers and/or a hormone called leptin—they do know that raised TSH levels lead to the rapid reproduction of fat cells (adipocytes).

Likewise, women with PCOS are more likely to be obese or overweight, which may be due to their higher baseline TSH levels.

Most women with hypothyroidism from Hashimoto's thyroiditis have elevated thyroid peroxidase (TPO) antibodies and a hypoechogenic thyroids, a pattern seen on ultrasound that is compatible with thyroiditis.

Similarly, research has found that women with PCOS have more hypoechogenic thyroids when compared to women without PCOS. Women with PCOS also have higher thyroid antibody levels (for example, TPO antibodies) and are more likely to have a goiter (enlarged thyroid gland).

While the features above suggest a definite link between PCOS and hypothyroidism, exactly what the relationship is, or how it will affect women's care, remains unknown.

Regardless, it seems sensible to discuss testing for one condition if you have the other, assuming your doctor has not already done so.