This is the last of a series of five blogs. In chronological order they are:
Shrinking penises, dropping sperm counts and bigger heads: What’s going on here?
Temperament, Testosterone and 21st Century Culture: More on “What’s going on Here”?
Sperm, testosterone and penises: Male reproductive health in crisis.
Temperament, Final sperm comments and the Declining Male Brand.
Boys and Men in Crisis. Biology? Culture? Both!
Part I: What physical and social forces affect testosterone levels in men?
We have known for awhile that male testosterone levels have a lot of variability. There is a circadian rhythm, with T highest in the morning and dropping slowly through the day. There is even a seasonal pattern with T lowest in the spring. Midline obesity (waist and belly) produces its own testosterone disruptor in the release of estrogen from fat cells. (Strange but true, and not true in other areas of fat accumulation). This type of fat reduces adult levels of testosterone in many men. T also drops slowly with age and with decreasing muscular fitness.
More relevant here is the fact that adult levels of testosterone are also vulnerable to events in the social environment. For an obvious example, sexual arousal increases testosterone in multiple circumstances. Watching an explicit movie is enough to raise the level 35% and this does not peak until 60 to 90 minutes later. T even increases when men have brief conversations with women. Wikepedia reports that “Men who have sexual encounters with unfamiliar or multiple partners experience large increases the morning after.”* They also note that “Men who watch sexually explicit films also report increased optimism and decreased exhaustion.
That last finding about increased optimism is interesting and important. We naturally think of testosterone as simply a sexual hormone, but studies of men with low T have shown a number of other important functions supported by it. Maintaining good muscle/bone mass and strength is one important role. However, quoting again from Wikipedia* “Literature suggests that attention, memory and spatial ability are key cognitive functions affected by testosterone in humans. Preliminary evidence suggests that low testosterone levels may be a risk factor for cognitive decline and possibly for dementia of the Alzheimer’s type.” More recently, good new research indicates that testosterone may be protective against depression in men.** A large scale study in 2008 found that older men with low levels of T were 271 % more likely to have “clinically significant signs of depression” than those with normal levels. In general, women are far more likely to have serious depression than are men and this continues to about age 65, when the difference fades away. It is thought that this action of testosterone may explain at least part of this difference. Continue reading