In nearly every culture on earth women outlive men — significantly so in the oldest years. But the men who do survive to become elderly are hardier than the women. A US National Institute of Aging study showed that 44% of men over age 80 are "robust and independent" compared with only 28% of women. And the percentage of surviving males increases from 15% at age 100 to 40% at age 105 in the United States.
If aging has been programmed by evolutionary forces, sex could be a very important contributor to the program. The reproductive organs of the human female exhibits a rate of aging that is among the most rapid of body systems. The complete shutdown of female fertility at menopause may be of value in preventing the birth of deformed children or death in childbirth of a mother who has several dependent children. For a species with a lengthy parenting period, it makes sense for fertility to cease long before the debilities of advancing age begin. Gonadotropin hormones from the pituitary gland are controlled by gonadotropin-releasing hormone, a 10-amino-acid peptide originating in neurons located in the arcuate nucleus of the hypothalamus. The two gonadotropin hormones (FSH & LH) are the same for females as for males, although their function is very different. Simplistically, FSH stimulates egg production in females & sperm production in males, whereas LH stimulates estrogen production in females & testosterone
production in males.
In fertile females FSH (Follicle-Stimulating Hormone) accelerates the growth of 6−12 primary follicles in the ovary each month — one of which may become a mature ovum. The follicles secrete estrogens, the most powerful of which is estradiol. A sudden increase in LH (Luteinizing Hormone) usually triggers ovulation (follicle rupture with discharge of the ovum) and the conversion of the follicle to the corpus luteum ("yellow body") — which also secretes estrogen, but primarily secretes progesterone. Progesterone stimulate the walls of the uterus to prepare it for implantation of the fertilized ovum. If pregnancy occurs, progesterone inhibits ovulation (by suppressing FSH & LH) and promotes uterine development until the placenta becomes more mature. (Progesterone is so-named because it promotes gestation, ie, the growth of offspring in the womb).
Aside from their role in the monthly cycle, estrogens are responsible for the development and maintenance of the female sexual organs, cause the deposition of fat in the breast&buttocks (which contributes to the feminine figure) and have a potent effect on bone development.
Menopause is the event in a woman's life when her ovary literally runs out of eggs. The loss of follicles to produce estradiol causes an end to menstrual cycling and production of estrogen & progesterone by the ovary. At age 30, a woman's period is normally 28−30 days, but by age 40 her period is typically closer to 25 days and her rate of egg-loss has accelerated. Further shortening (accompanied by periods when no ovulation occurs) eventually leads to menopause at an average age of 50 (plus or minus 10 years). The menopausal woman often experiences anxiety, irritability and fatigue. Beginning before menopause most women experience "hot flashes", ie, 3 minute surges of blood to the skin of the chest, shoulders & face leading to sudden hotness & sweating. Hot flashes are associated with a pulsatile release of LH from hypothalamic neurons associated with body temperature elevation. Estrogen therapy eliminates hot flashes. The rate of loss of ovarian follicles doubles around age 35, raising the suspicion that a hypothalamic mechanism may be the ultimate cause of menopause [SCIENCE 273:67-70 (1996)].
Graph of Female Hormonal Cycles
The most serious complications of menopause are osteoporosis and a decline in cardiovascular health. The Framingham Heart Study demonstrated that between ages 35 to 65 men have 10 times the incidence of heart attack as women — probably because estrogen protects against heart disease. Estrogen elevates HDL cholesterol and reduces LDL cholesterol in the bloodstream.
After menopause, nipples decrease in size and the surrounding alveolar tissue shrinks. Erection of these tissues with external stimulation is more difficult. Vaginal contractions during orgasm is reduced to 4−5 at 0.8-second intervals from 8−12 in young adults.
The testes have been regarded as the source of maleness at least since ancient Rome, where eunuchs & women were not permitted to "testify" (testis is Latin for "witness"). In the male, LH stimulates secretion of testosterone by the interstitial cells of Leydig in the testes. FSH stimulates spermatogenesis in the seminiferous tubules of the testes. Testosterone promotes development of male sexual organs in the foetus. At puberty testosterone stimulates hair growth on the face & pubis, causes enlargement of the larynx to deepen the voice, increases skin thickness, causes a 50% increase in muscle mass, promotes bone growth, increases basal metabolism up to 15% and increases red blood cell concentration.
There is no sudden "andropause" event in males that is comparable to the menopause event of females. Instead, testosterone levels tend to decline gradually with age. This decline occurs most dramatically in those with cardiovascular disease or a predisposition to adult-onset diabetes. Although sperm count declines, fatherhood has been verified for a male as old as 94. Semen production declines in the prostate as a man ages — and the smooth muscle is replaced by overgrowing connective tissue that enlarges the prostate, blocks urine and can lead to cancer. 85% of men over age 50 have symptoms arising from benign prostatic hyperplasia — a noncancerous overgrowth of prostate tissue possibly caused by excessive expression of the anti-apoptosis protein bcl−2 [HUMAN PATHOLOGY 27:668-675 (1996)]. In some tissues testosterone must be converted to dihydrotestosterone (by the enzyme 5−α reductase) in order to act. This occurs most notably in the prostate gland, which produces semen (a mixture of sugars, protein and water). Dihydrotestosterone has also been implicated in baldness. The European drug Permixon (an extract of the saw palmetto berry) inhibits 5−α reductase, and is used to prevent prostate hypertrophy and prostate cancer. The Life Extension Foundation sells saw palmetto berry extracts as a dietary supplement for this purpose.
Testosterone has been used in elderly men for "rejuvenation" — to restore virility & muscle strength. Testosterone increases the risk of cardiovascular disease — by increasing blood pressure, by lowering HDL cholesterol and by elevating LDL cholesterol. These same dangerous side effects are also seen in athletes who attempt to use androgens or other anabolic steroids to improve athletic performance. Eunuchs reportedly live longer, although there have been no controlled clinical trials to prove this
observation. Sterilization of a dog or cat (male or female) adds a couple of years to its lifespan. Any reduction in sex hormones would be expected to reduce cell proliferation and hence reduce the probability of cancer.
Male libido peaks in mid-adolescence, and does not correlate exactly with testosterone blood levels. In elderly men it may take from 10 seconds to several minutes to get an erection, in contrast to 3−5 seconds in young men. Contractions of the penile urethra during orgasm is reduced to 1−2 contractions per 0.8-seconds from 3−4 in young adults. Ejaculatory distance is reduced from 12−24 inches to 3−5 inches.
