This issue comes up from time to time. I have been contemplating an answer that will be accurate and not highly complex. Unfortunately the entire subject requires a knowledge of embryology, physiology and histology. Please understand that I do not say that to imply that the list members will not be able to understand it, only that my ability to explain it may be lacking.
The vocal folds undergo thickening under the influence of testosterone at puberty. There is some growth for women also, but it is not in the same way as in men. The larynx itself grows also in addition to the pharynx, jaws, nasal passages and so on.
A woman's vocal folds and muscles maintain their structure under the influence of her estrogen. Depending on the balance of estrogen and progesterone, she has more or less variation throughout the menstrual cycle. If she has "normal" weight, things cycle normally. Normal differs for every woman. That is why some women have vocal problems at the menses and some do not. Birth control pills can benefit, harm or have no effect depending on the balance of hormones and how they are metabolized in her body. The effect is similarly variable with hormone replacement after menopause.
The body weight affects how much estradiol (E2) is converted to estrone (E3). E3 is longer lasting and very estrogenic in certain tissues. E2 is converted to E3 in fat. The number of estrogen receptors in various tissues is genetically mediated. A woman with a lot of estrone, a lot of estrogen receptors on her vocal apparatus and low levels of progesterone will have an entirely different type of effect from her weight than a thin woman with few estrogen receptors. The fat also can convert adrenal intermediates into androgen-like hormones or not depending on the woman's genetic makeup.
Some overweight women have polycystic ovary syndrome. In this situation, she may have too much testosterone and other androgenic hormones.
If a woman has less than about 10 percent body fat, such as, through anorexi a nervosa or other process, her E3 levels fall. There is feedback to the hypothalamus and pituitary to reduce the surge of two hormones responsible for stimulating ovulation (this is probably a survival feature to prevent conception during a period of inadequate calories). The normal cycling is inhibited allowing a reduction in estrogen due to lower pituitary stimulation. The voice can be affected if it has not reached maturation most likely, but unless she is at the point of malnutrition, if her voice is formed, it will likely stay OK. This disregards the effects of estrogen receptor levels.
There are so many ifs, ands and buts that there is no one correct answer to the question of weight and hormones and singing. I will point out that fat cells do not absorb testosterone or anything else besides fat.
Unfortunately, the complete explanation requires a lot more reading in medicine and physiology. There are many aspects that are not even known due to the extreme variability in E2, E3, progesterone and testosterone levels in women.
I hope this shed some light on this complex issue.
John
John J. Messmer, M.D. Assistant Professor, Family & Community Medicine Penn State College of Medicine
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