Androgenic alopecia is related to hormones called androgens, particularly an androgen called dihydrotestosterone (DHT).
In women, the hair becomes thinner all over the head, and the hairline does not recede. This is dubbed "Female pattern baldness" and may occur in males.
Male pattern baldness is caused by a genetic sensitivity of hair follicles to DHT, which causes them to shrink or "miniaturize" when exposed to it. This shortens their lifespan and prevents them from producing hair normally.
Men with androgenic alopecia typically have higher levels of 5-alpha-reductase, lower levels of total testosterone, higher levels of unbound/free testosterone, and higher levels of total free androgens including DHT.
5-alpha-reductase is responsible for converting free testosterone into DHT. The 5-alpha-reductase enzymes are present predominantly in the scalp and prostate.
Sex hormone binding globulin (SHBG), which is responsible for binding testosterone and preventing its bioavailability and conversion to DHT, is typically lower in individuals with high DHT. SHBG is downregulated (ie, decreased the quantity) by insulin.
Increased levels of Insulin Growth Factor-1 (IGF-1) have been correlated to vertex balding.
Lower insulin levels and reduced stress both result in raised levels of sex hormone-binding globulin (SHBG). SHBG binds to testosterone.
Only free testosterone improves muscle growth and insulin sensitivity, but free testosterone can also be converted to the ineffective (regarding insulin sensitivity) DHT. The levels of free androgens and not of total androgens are relevant to the levels of DHT in the scalp and the progression of male pattern baldness. In short, aerobic exercise is capable of significantly lowering DHT.
Androgenic alopecia correlates with metabolic syndrome because typically bald men have low testosterone levels (hypogonadism) which can easily trigger also diabetes mellitus and erectile dysfunction. [...] behaviors which help to keep insulin levels low and reduce chronic inflammation might also help to preserve hair.
Dihydrotestosterone (DHT) is an androgen, synthesized primarily in the prostate gland, testes, hair follicles, and adrenal glands by the enzyme 5α-reductase.
DHT is the primary contributing factor in male pattern baldness. DHT plays a role in the development and exacerbation of benign prostatic hyperplasia, as well as prostate cancer, by enlarging the prostate gland. Prostate growth and differentiation are highly dependent on sex steroid hormones, particularly DHT.
The drugs belonging to the 5α-reductase inhibitors group are commonly used for the treatment of those conditions. Dutasteride is approved for the treatment of BPH and is prescribed off-label for the treatment of MPB, whereas finasteride is approved for both conditions. Dutasteride is three times more potent than finasteride in inhibiting the Type II enzyme and 100 times more potent than finasteride in inhibiting the Type I form of the DHT-producing enzyme.
Inhibition of 5-alpha reductase results in decreased production of DHT, increased levels of testosterone, and, perhaps, increased levels of estradiol. Gynecomastia is a possible side-effect of 5-alpha reductase inhibition.
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