Hair loss and hormones: what is the cause?

Which endocrine diseases cause hair loss?

• hypothyroidism – reduced thyroid function;
• hyperthyroidism (thyrotoxicosis), including Graves’ disease – increased thyroid function;
• diabetes mellitus;
• excess testosterone in women;
• DHT activity in men;
• polycystic ovary syndrome (PCOS);
• autoimmune processes (for example, lupus).

How does the thyroid affect hair?

For hair and even eyebrows to stay strong, there must be enough thyroid hormone in the blood. When thyroid hormone is lacking, the whole metabolism slows down and the absorption of vitamins and minerals from the gut weakens – and this plays a big role in hair loss. An overactive thyroid also causes thinning and shedding.

With a thyroid hormone imbalance, the hair first becomes thinner, grows more slowly and starts falling out more than usual.

Patients taking thyroid medication sometimes complain of hair loss. These medicines do not increase hair loss in themselves, but if the dose is too high or too low, hair may fall out. In that case hormones should be measured again, and iron and zinc deficiency and anaemia should also be checked. If hair loss continues after hormone levels return to normal, other hormones should be examined.

Why do iron, ferritin and vitamins matter?

Iron is needed to make haemoglobin, which carries oxygen to the hair follicles as well. When follicles do not get enough oxygen and nutrients, they weaken, and hair becomes thin, brittle and sheds more. Since iron-deficiency anaemia and hair loss are very common, especially in women, iron deficiency should be ruled out first.

Ferritin is the most sensitive marker of the body’s iron stores. In women it drops quickly because of monthly blood loss, stores depleted by pregnancy and childbirth, long and heavy periods, and diets low in meat and protein. Low ferritin may show up not only as hair loss but also as constant fatigue, shortness of breath, brittle nails and sensitivity to cold.

It is important not only to get enough iron but also to absorb it well. Coeliac disease, and taking iron-rich foods together with calcium-rich foods, tea or coffee, can interfere with iron absorption.

Hair loss is one of the signs of vitamin B12 deficiency. Among the main causes of anaemia that develops in adulthood are iron deficiency as well as B12 and folic acid deficiency. Zinc is an important mineral for healthy hair and skin.

Vitamin D deficiency is widespread, and its level is often checked in patients who come with hair loss. However, taking vitamins on your own without tests is not the right approach.

PCOS and male hormones

Male-pattern hair loss in women results from increased testosterone, the male hormone, in the blood. Hair thins at the crown or along the forehead. Together with increased body hair, irregular periods and acne, it is one of the key signs of high androgens.

Elevated androgens usually come from the ovaries and adrenal glands; one of the main causes is polycystic ovary syndrome. In such cases ovarian and adrenal hormones need to be examined.

Which tests may be needed?

Your doctor decides which tests you need based on your complaints. The most commonly checked are:

• thyroid hormones (TSH, free T4);
• ferritin and a complete blood count for anaemia;
• zinc;
• B12 and vitamin D;
• in women with male-pattern hair loss, excess body hair or menstrual disorders – testosterone and other hormones, hormone tests on days 2–5 of the menstrual cycle and an ovarian ultrasound.