Hypothyroid/Hyperthyroid & Hair Loss

Written by Philip Kingsley Trichologist, Elizabeth Cunnane Phillips.

Hypothyroid and hyperthyroid hair loss: what's the difference?

How the thyroid affects your hair

Both an underactive thyroid (hypothyroidism) and an overactive one (hyperthyroidism) can cause hair thinning and shedding, because thyroid hormones regulate the energy available to every cell in the body, hair follicles included. When hormone levels fall outside their normal range, hair growth is often one of the earliest visible signs, alongside fatigue, weight changes and mood changes.

What the thyroid does

The thyroid is part of the endocrine system, a butterfly-shaped gland situated in the lower neck, just below the Adam's apple and wrapped around the windpipe. It's composed of two lobes either side of the isthmus, the bridge connecting them; each lobe performs the same function and, much like the kidneys, can take on extra work if the other is compromised. Despite weighing only around an ounce, it affects every cell in the body.

The thyroid's single function is producing hormones released into the bloodstream. The brain's hypothalamus signals the pituitary gland to produce TSH, which in turn tells the thyroid to make thyroxine (T4) and triiodothyronine (T3), together known as thyroid hormone. These control metabolism and how much energy different body systems need; the pituitary gland reads hormone levels in the blood and adjusts T3 and T4 production accordingly.

Hypothyroidism (underactive thyroid) and hair loss

Hypothyroidism is one of the most common health problems in adults, meaning there isn't enough thyroid hormone (T3 and/or T4) circulating in the body. It ranges from mild to severe. Low hormone levels reduce the body's ability to regenerate cells; Iodine insufficiency is a primary cause in developing regions, while in developed countries, Hashimoto's disease, an autoimmune condition where white blood cells attack the thyroid, is responsible for up to 80% of cases according to the American Association of Clinical Endocrinologists. Women are five times more likely to be diagnosed than men, with the odds increasing with age.

Symptoms of an underactive thyroid include:

• Cardiovascular changes and cold sensitivity

• Depression and/or anxiety

• Weight gain without dietary or exercise changes

• An enlarged thyroid gland, often called a goitre

• Persistent fatigue, even after a full night's sleep

• Brittle nails, which may develop ridging

• Dry, brittle hair with visible thinning, along with changes in eyebrow, leg, arm and pubic hair, often the symptom that brings people to a Trichologist

• Elevated cholesterol, muscle cramping, memory and concentration changes, and dry, itchy skin

From a Trichology perspective, the added concern is that anaemia or low iron, often linked to heavy periods, can compound hair loss and density changes alongside a thyroid imbalance.

Hyperthyroidism (overactive thyroid) and hair loss

Hyperthyroidism results from an overproduction of T3 and T4. A large proportion of cases are caused by Graves' disease, an autoimmune condition in which the immune system attacks the thyroid, producing antibodies that push the thyroid to make excess hormone regardless of what the body actually needs.

Symptoms of an overactive thyroid include:

• Weight loss without dietary changes or exercise

• Hand tremors and difficulty concentrating

• Frequent, typically loose bowel movements

• Thinning hair and excess shedding

• Increased sweating and heart palpitations

• Dry eyes, light sensitivity and, in some cases, protruding eyes

• A visibly enlarged thyroid (goitre), insomnia and menstrual problems

When to see a doctor

General and conventional wisdom suggests that if you can say yes to three or more of the symptoms on either list it is time to speak with your doctor and discuss the need for a thorough evaluation.

If three or more symptoms from either list sound familiar, it's worth speaking to your doctor about a thorough thyroid evaluation rather than waiting for things to resolve on their own.

General dietary advice that supports thyroid health includes limiting processed foods where possible. It's rarely a single serving that causes problems, but long-term accumulation; mercury is a classic example, since it's chemically similar to iodine, so the thyroid stores it, and this can potentially trigger autoimmune thyroid conditions such as Graves' or Hashimoto's. As with any health concern, getting a proper diagnosis, agreeing a treatment plan with your doctor, and following up matters more than any single piece of dietary advice.