The Impact of Birth Control Pills on Thyroid Hormone Balance

Introduction

In hypothyroidism, the thyroid gland does not produce sufficient thyroid hormone. Birth control pills contain female sex hormones like estrogen and progesterone in the synthetic form. The combination of both comes in various forms. Birth control pills are available as patches, oral contraceptives, vaginal rings, and shots. Synthetic estrogens alter the thyroid hormone levels produced by the thyroid gland. It decreases the levels of thyroid hormones leading to hypothyroidism (underactive thyroid).

What Is the Function of Thyroid Hormones in the Body?

The functions of the thyroid gland are:

• The thyroid gland is in the neck below the larynx (voice box).

• The thyroid gland hormones regulate the heart and digestive system and help in bone and brain development. The hormones produced are thyroxine (T4) and triiodothyronine (T3). These hormones help regulate body weight, heart rate, muscle strength, breathing, blood lipid (fat) levels, menstrual cycle, and body temperature.

• It has an impact on every cell and organ. The thyroid hormone T3 controls the production of many proteins in the body’s cells by binding to the cell’s DNA (deoxyribonucleic acid).

• The thyroid hormone T4 is converted into T3, and the T3 binds to the specific T3 receptors in the nucleus. This bound T3 hormone stimulates the synthesis of specific proteins.

• The pituitary gland in the brain controls thyroid hormone secretion by releasing thyroid stimulating hormone (TSH), causing the release of T3 and T4. Excess T3 hormones inhibit the release of TSH from the pituitary gland, thus forming a negative feedback loop. So higher T3 concentration lowers the TSH levels in the body.

The thyroid hormone is important for the following functions:

• Normal growth.

• Regulation of body temperature.

• Digestion.

• Brain development.

• Production of energy.

What Is Hypothyroidism?

Hashimoto's thyroiditis is an autoimmune disorder that causes hypothyroidism. The symptoms of hypothyroidism are:

• Weight gain.

• Fatigue.

• Dry skin.

• Depression.

• Tolerating cold.

• Muscle and joint pain.

• Slow heart rate.

How Does Birth Control Work?

The working process of birth control is described below:

• Birth control pills are the most popular methods of preventing pregnancy. Birth control pills contain hormones that include progesterone and estrogen.

• Birth control pills are available in some forms, like shots, patches, hormonal intrauterine devices (IUDs), and vaginal rings.

• The estrogen in birth control pills alters how thyroid hormones are produced and used. The small amount of estrogen in the pills prevents ovulation by inhibiting the body's natural hormones.

• Hormonal contraceptives prevent the body from ovulating. Oral contraceptive pills contain estrogen and progestin to prevent pregnancy.

• There are three types of pills. They are - progestin-only pills, combination pills, and extended-use pills. Most of the pills contain 20 to 35 micrograms of estrogen along with progestin. Some pills have less than 10 micrograms of estrogen.

Can Birth Control Pills Affect the Thyroid?

The effects of OCP on the thyroid gland are described below:

• The estrogenic effect of birth control pills increases various proteins synthesized by the liver. The proteins include thyroxine-binding globulin (TBG).

• If the thyroxine-binding globulin (TBG) is very high, then it binds to more thyroxine hormones leaving less free circulating thyroxine. This leads to the release of more thyroid gland-stimulating hormone, which causes more production of thyroid hormones.

• Increased estrogen resulted in decreased thyroxine-binding globulin renal clearance, leading to increased TBG available for binding to thyroid hormones. The increased thyroxine-binding globulin causes decreases in the circulating thyroid hormone.

• The brain's hypothalamus and the anterior pituitary gland regulate thyroid hormone synthesis. The hypothalamus releases TRH (thyroid-stimulating hormone), which stimulates the anterior pituitary gland to release thyroid-stimulating hormone (TSH).

• The increased levels of TSH trigger the thyroid gland to produce more thyroxine hormone.

• Estrogen in the OCP causes an increase in thyroxine-binding globulin (TBG) levels.

• Thyroxine-binding globulin is a liver protein that moves thyroid hormones through the circulatory system.

• When the thyroid hormone globulin protein level increases, the available free thyroid hormone decreases.

• The thyroid gland needs specific minerals and vitamins to make the thyroxine hormone.

• Magnesium, selenium, and zinc are important in overall thyroid function.

What Are the Effects of Birth Control Pills on the Thyroid Gland?

The effects of birth control pills on the thyroid gland are described below:

• It increases the thyroid hormone levels (T3 and T4).

• It alters thyroid function tests.

• It increases the risk of hypothyroidism in individuals who are taking medications for thyroid.

• It exacerbates autoimmune thyroid disorders.

• Birth control pills increase the risk of thyroid nodules or thyroid cancer.

What Is the Diagnosis of Hypothyroidism?

The tests for diagnosing hypothyroidism include:

• Blood Tests - Blood tests are done to diagnose hypothyroidism. It measures the level of thyroid-stimulating hormone in the blood.

• Thyroid-Stimulating Hormone (Tsh) Test - The diagnosis is hypothyroidism if the test shows high thyroid stimulating hormone and low thyroxine hormone. If the TSH levels are high and thyroxine hormone levels are standard, it is called subclinical hypothyroidism. The main test for diagnosing hypothyroidism is called the thyroid stimulating hormone (TSH) test. The thyroid-stimulating hormone levels are normally between 0.4 to 4.5 milliunits per liter (mU/L).

The TSH levels higher than 4.5 mU/L indicate an underactive thyroid, and TSH levels below 0.4 mU/L indicate an overactive thyroid (hyperthyroidism). If a high TSH suggests an underactive thyroid gland (hypothyroidism), low TSH levels indicate an overactive thyroid.

• Other Tests - TSH, T3, T4, and thyroid antibody blood tests, imaging tests, and thyroid scans or ultrasound scans are done to uptake test measures of radioactive iodine that the thyroid takes up from the blood.

What Is the Treatment for Hypothyroidism?

The treatment for hypothyroidism depends on the severity of the symptoms. Some of the common treatments for hypothyroidism are:

• Levothyroxine is a synthetic hormone that replaces the missing thyroid hormone in the body. It is taken preferably in the morning, and the dosage depends on the patient's weight, age, and other medical conditions.

• Liothyronine is also a synthetic hormone that contains only the T3 hormone. Liothyronine is given when Levothyroxine does not work or when the patient has difficulty converting T4 to T3.

• Some dietary changes such as increasing iodine intake can help improve thyroid function and foods rich in iodine are seaweed, fish, dairy products, and eggs. Additionally, broccoli, cabbage, and soy can help reduce inflammation in the thyroid gland.

Conclusion

Estrogen-containing oral contraceptive pills decrease the circulating thyroid hormone levels leading to hypothyroidism. It increases the thyroid hormone-binding protein (THB) level, eventually decreasing thyroid hormone levels. To normalize the thyroid hormone levels, the patient is given high doses of thyroid hormones. Once the person stops taking the estrogen-containing pills, the thyroid medication can be given in low doses. The person taking Levothyroxine (synthetic T4) or Liothyronine sodium (synthetic T3) should be monitored for six to eight weeks after the birth control pills are started.