Hair loss is brought up on both hyperthyroid and hypothyroid forums, and those who have been both, like me, have noticed their hair coming and going. So what exactly is required for good hair? There are few human studies to cite, but there’s a lot of anecdotal evidence that I can report, and some of my own theories.
Hair cycles through a growth phase called anagen, a regression stage called catagen, a resting phase called telogen, and finally, the hair is shed in the last stage called exogen. I believe that when someone is hypothyroid, their whole body is in slow motion, so their hair stays in the resting phase far longer than normal. That means no new hair grows until there’s enough thyroid hormone to start the growth phase again. There is probably a minimum level of both T4 and T3 (the two thyroid hormones) required for normal hair growth. If you’re only on T4 or levothyroxine, then you might need to add a small amount of T3 to get your hair growing again. (A normal human secretes, on average, about 10 mcg of T3 daily.) Note, however, that T3 cannot be tolerated in those with insufficient iron or cortisol levels, so those need to be tested and addressed too. Cortisol, iodine, iron, selenium, zinc, and Vitamin A are all required for normal thyroid metabolism.
Hair loss is also reported by people with Graves’ Disease who are hyperthyroid, or on the T3-only protocol, or even on high doses of desiccated thyroid. They’ve got plenty of T3, so what’s the problem? Well unlike the hypothyroid body that’s in slow motion, a hyperthyroid body is moving at warp speed. Each strand of hair has a limited lifespan, and it progresses through all the stages sequentially. But the rate of the progression would be greatly increased in someone with too much T3. Maybe hair cycles too quickly with too much T3 and finishes the growth stage and enters the resting stage prematurely. My hairdresser noted that my hair strands were thinner when I was on too much T3. The other possibility is that too much T3 simply overwhelms the hair follicles, in the same way that it causes damage to other parts of the body. Excess T3 causes bone loss and muscle wasting, so the same type of mechanism may be at work that causes hair loss too.
T4, or levothyroxine, seems to have a positive effect on many patients’ hair. I know my hair improved when I went from 100% desiccated thyroid to a combo with T4. My hairdresser said my individual hair strands are thicker now. And I have heard multiple anecdotal accounts reporting the same thing. While some cells pull T3 straight out of the bloodstream, other cells prefer to get their T3 by conversion from T4. That way, the cells are never overwhelmed with an excess of T3. I believe hair follicles prefer T4 and know people on 100% T4 who have full heads of hair, but the lack of T3 causes other problems for them, like weight gain.
Hair loss may also be caused by androgenic hormones like DHEA or testosterone, which contribute to androgenetic alopecia or male pattern baldness. Even pregnenolone can convert into testosterone in some women. This is a male pattern type of hair loss, which consists of a receding hairline and hair loss at the temples. Low thyroid hair loss is usually a general thinning throughout the entire scalp. Evening primrose oil appears to help male pattern hair loss, and I’ve noticed positive effects from this supplement.
If your hair started thinning around menopause, then test your estradiol and progesterone levels and consider bioidentical hormone replacement. Healthy hair requires good levels of both hormones.
Vitamin D has positive effects on skin and hair too, so don’t ignore that supplement if your levels are low. Of course, as with all supplements mentioned, be aware of adverse reactions. People have had negative reactions to Vitamin D, iodine, iron, zinc, and hydrocortisone (for cortisol), even though they are all found in the human body.
Both thyroid hormones, T3 and T4, need to be at good levels for an individual to have healthy hair. Hair and eyebrows are really non-essential, and if there’s a deficit of thyroid hormone, the body will skimp on the hair’s portion and allocate it to more important organs where it’s needed. In general, good health is found when both Free T3 and Free T4 are in the upper half of the range. If raising T3 has not helped your thin hair and in fact made it worse, perhaps you need more T4 instead of more T3. Read more about optimal thyroid labs and misleading reference ranges.