Figure 24-17Drastic changes in estrogen levels affect mood.

In a randomized, controlled, double-blind study, researchers injected 47 men each week for six weeks with large amounts of testosterone and made numerous measurements of each participant’s physical state. The testosterone caused more than just physical changes, though; after six weeks, one man said, “I feel great! I’m confident, happy, and productive. I want to be on this stuff forever.” The researchers said that this was a common response among the study’s participants.

Not only do hormones affect our physical traits and performance, they can also influence how we feel. Many hormones have pronounced effects on moods, defined as relatively long-lasting emotional states (shorter-lasting than a person’s temperament, but longer-lasting and less specific than a single emotion). Here we describe just a few of the documented effects of hormones on mood in humans.

Estrogen In women, the levels of estrogen in the bloodstream change throughout life. And the incidence of depression follows a similar pattern. The large increases in estrogen levels at puberty, the sharp drop-off in estrogen levels after a woman gives birth, and the reduced estrogen levels at the onset of menopause are all associated with increased occurrence of depression (FIGURE 24-17). Estrogen as part of hormone replacement therapy is effective at reducing depression in women going through menopause.

Interestingly, researchers investigating the effect of hormones on mood discovered that women exposed to a male partner’s semen during sex rated their mood as happier than those using condoms. The effect is believed to be a consequence of the mood-altering effects of the testosterone and estrogen that are present in semen and are absorbed through the vagina. (With unprotected sex, however, the potential for sexually transmitted diseases or unwanted pregnancy must also be factored into any long-term assessment of mood, complicating the research findings.)

Testosterone Many studies have demonstrated a link between testosterone and mood in human males, including increased self-esteem and a sense of overflowing with new ideas. In the study discussed above, the men were described by their significant others as energetic, euphoric, confident, and charismatic. In a small number of cases, however, the men became uncharacteristically aggressive and exhibited verbal hostility. The researchers even had to withdraw one participant from the study when he became “alarmingly” aggressive—consistent with anecdotal claims of so-called ’roid rage resulting from supplemental testosterone.

Several studies on competitive male athletes have documented that testosterone levels—and the mood changes they influence—rise prior to a competition. After the contest, testosterone levels in the losers of the competition drop quickly and dramatically, while testosterone levels in the winners remain high and sometimes even increase (FIGURE 24-18).

Figure 24-18Biological victory dance. Testosterone levels surge in victorious competitors and in fans, too.

Recent studies reveal that sports fans share in this biological “victory dance.” Measurements of testosterone levels in male fans of Brazilian and Italian soccer teams during World Cup finals (and replicated in fans of a college basketball team) revealed that the testosterone levels of the fans of the winning team rose, but not those of the losing team.

Figure 24-19Hiding in the dark. Rodents exposed to cortisol show anxious behavior.

Melatonin In randomized, controlled, double-blind studies, researchers have demonstrated that under certain conditions, oral melatonin can induce hypnotic, sedative-like effects and improve sleep efficiency. Other studies showed that, in comparison with placebo treatment, melatonin supplementation significantly reduced participant’s self-reported vigor, while increasing their fatigue and confusion.

Cortisol The majority of individuals suffering from Cushing’s disease, a condition in which the adrenal glands release unusually large amounts of cortisol, experience depression and anxiety. Also, an atypically high number of individuals treated with cortisone (a chemical variant of cortisol) to reduce tissue inflammation suffer from anxiety and depression. As a consequence of these observations, researchers conducted a controlled study exposing rodents to cortisol in their drinking water. Two weeks or more of cortisol exposure caused the animals to take significantly longer to emerge from small, dark compartments into a brightly lit area—a measure of anxiety-like behavior in rodents—as compared with animals not exposed to the cortisol (FIGURE 24-19).