. "5. Hormonal Mediation of Physiological and Behavioral Processes That Influence Fertility." Offspring: Human Fertility Behavior in Biodemographic Perspective. Washington, DC: The National Academies Press, 2003.
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Offspring: Human Fertility Behavior in Biodemographic Perspective
age between plasma testosterone levels and degree of sexual desire and sexual activity (Halpern et al., 1998; Udry et al., 1985).
In females the rising tide of estrogen at puberty is the primary stimulus for development of most of the secondary sexual characteristics, including breast development, widening of the hips, and increased deposition of subcutaneous body fat. The growth of axillary and pubic hair is under androgenic control and is stimulated by an increase in dehydroepiandrosterone (DHEA) from the adrenal gland. This developmental increase in DHEA is referred to as adrenarche and generally precedes puberty by several months to several years. Increases in sexual desire and sexual behavior also occur in girls at puberty. And, as in adulthood, there is controversy as to which hormones may be mediating these increases. There are correlations between androgen levels in adolescent girls and sexual interest (Udry et al., 1986) and the initiation of coitus (Halpern et al., 1997). However, the role of estrogens, which tend to covary with androgens in females, has not been adequately examined. Moreover, there is evidence that social factors can be as important as hormonal factors in determining a girl’s sexual behavior (Udry et al., 1986).
Changes with Aging
In males, testosterone levels decrease slightly with aging and there is a mean decrease in sexual behavior, although again there are large individual variations (Meston and Frohlich, 2000). Although there have been a number of reports showing an improvement in libido and erectile function in older men with testosterone and dihydrotestosterone treatment (Bain, 2001; Kunelius et al., 2002; Morley, 2001; Nolten, 2000), these have been uncontrolled open studies, with no large-scale multicenter prospective studies performed to date. Moreover, although there is fairly consistent data showing that decreases in libido and sexual activity can occur with progressive age in males (Bain, 2001; Morales and Heaton, 2001; Nolten, 2000), there is a large degree of individual variability, and within individuals who have normal testosterone levels there is no correlation between libido and testosterone levels (Rhoden et al., 2002). Most men continue to produce sperm and remain fertile well into old age. In recent years recognition that the adrenal androgen DHEA decreases with aging has led to the popular notion that DHEA treatment may increase libido and erectile function. However, several controlled double-blind studies have failed to show significant effects of DHEA supplementation on sexual function (Flynn et al., 1999; Hermann and Berger, 2001; Reiter et al., 1999).
Changes in reproductive physiology with aging are much more dramatic in females (Burger et al., 2002). The term “menopause” refers to a woman’s last menstrual cycle. During the transition to ovarian quiescence