The thyroid gland is crucial in maintaining the body’s metabolism by controlling the production of proteins and tissue utilization of oxygen, thus affecting the hair follicles. Understanding thyroid function and its effect on hair growth is very complicated, and I do not want to tempt you to blame a thyroid dysfunction for your hair fall or thinning hair. On the other hand, it may be useful for you or your doctor to realize that there is a possibility of having thyroid readings in the normal reference range but it still having an effect on your hair. That is, as with many blood test results, low normals or high normals can be one of the triggers.
Hypothyroid (low) or hyperthyroid (high) definitely affects hair adversely, but these are easily diagnosed by low or high thyroid testing levels. It is the ones on the cusp that sometimes need a mild degree of medication, but it is only available on prescription. However, your doctor may be reluctant to prescribe it if you are in the normal reference ranges.
A further complication is that thyroid production can be affected by other conditions: drugs, oral contraceptives, pregnancy and menopause for example. Long-standing hypothyroids may result in anaemia; people from developing countries may suffer from low iodine intake, which effects the thyroid and therefore the hair.
Two quite common thyroid diseases are Hashimoto’s (hypo) and Grave’s (hyper). Either of these would have other symptoms apart from hair loss. The high thyroids, for example, may have high blood pressure, a rapid heartbeat, increased sweating, insomnia, slightly protruding eyes and weight loss in spite of increased appetite. The low thyroids may experience, amongst other things, a slower pulse, hoarser voice, intolerance to cold, weight gain, thinner and dryer hair and loss of some eyebrow hair. If you begin to notice any of these, it would be as well to check with your doctor.
Almost without exception, women in particular will have had their thyroid checked before coming to see me for a hair problem -many of them having mild symptoms, but still just in the normal range where medication is deemed unnecessary. Hair sensitive or hair sympathetic doctors seem in the minority, and as with blood tests and measurements for iron levels, thyroid measurements are accepted without due regard to their effect on the hair.