The mechanisms that link obesity to ovarian function are not yet known in depth, although it appears that there is an alteration in the hypothalamus–pituitary–ovarian axis.[14] Excess adiposity increases the aromatization of androgens to estrogen, decreasing the hepatic synthesis of sex hormone-binding globulin (SHBG).[13,15] This increases levels of estradiol and circulating testosterone (raising the free androgenic index), and thus increases the risk of menstruation irregularities. This evidence concerns the gene SHBG and obesity disorder.