Testosterone, a hormone produced primarily in the testicles, plays a critical role in a man's life experience. It helps maintain bone density, fat distribution, sperm production, muscle strength and mass, and red blood cell production. When it ebbs, testosterone also makes itself felt; low testosterone levels may cause physical changes, such as increased body fat, reduced muscle bulk and strength, and decreased bone density. In some cases, testosterone replacement therapy may be prescribed in the form of injections, pellets, patches, or gels to improve the symptoms of low testosterone.

Despite the presence of other androgens — the hormones that stimulate or control development and maintenance of male characteristics — scientists believe testosterone is the key component to the sex drive. Testosterone levels peak in the late teens and then gradually decline over time, typically about one percent a year after age 30. By age 60 to 65, though usually earlier, most men notice that their sexual inclinations and sexual abilities have changed; it takes longer for the penis to become erect and their erections may not be as firm. It may also take longer to achieve orgasmic and ejaculatory experiences. Erectile dysfunction also becomes more common.

Men also produce estrogen, the female sex hormone, and women similarly produce both testosterone and estrogen. Over the years, in both men and women, the proportions of hormones change. This shifting balance may be responsible for changes in behavior as men and women age. For instance, as levels of estrogen decline in women and their levels of testosterone become proportionately greater, they may become more assertive; on the flip side, men may become less so as their levels seesaw in the opposite direction.

Most people believe changes in hormone levels and therefore the subsiding of the libido are a natural part of the aging process but recent studies refute, to some extent, these notions.

Behavioral Impact

A 2012 study finds that the waning of testosterone levels in men is more likely a result of behavioral and health changes than by aging. "Declining testosterone levels are not an inevitable part of the aging process, as many people think," said study co-author Gary Wittert, MD, professor of medicine at the University of Adelaide in Adelaide, Australia.

In a study supported by the National Health and Medical Research Council of Australia, Wittert and his co-authors analyzed testosterone measurements in more than 1,500 men who had measurements taken at two clinic visits five years apart. According to Wittert, all blood testosterone samples underwent testing at the same time for each time point. They included 1,382 men in the data analysis after excluding any men who had abnormal lab values or who were taking medications or had medical conditions known to affect hormones. The participants ranged in age from 35 to 80 years, with an average age of 54.

On average, testosterone levels did not decline significantly over five years; rather, they decreased less than one percent each year, the authors reported. However, when the investigators analyzed the data by subgroups, they found that certain factors were linked to lower testosterone levels at five years than at the beginning of the study.

"Men who had declines in testosterone were more likely to be those who became obese, had stopped smoking or were depressed at either clinic visit," Wittert said. Past research has linked depression and low testosterone.

Unmarried men in the study had greater testosterone reductions than did married men. Wittert attributed this finding to past research showing that married men tend to be healthier and happier than unmarried men. "Also, regular sexual activity tends to increase testosterone," he explained.

Regular activity as well as other factors increase desire and influence the male sexual response, according to other researchers.

Porn Drive

From the Italians, we learn that porn is having a negative effect on the sex drives of young healthy men — so say researchers who posit that more and more men are suffering from 'sexual anorexia' and are unable to get erections because of Internet porn use that started in their mid-teens.

A survey of 28,000 users found that many Italian males started an "excessive consumption" of porn sites as early as 14 years old. After daily use in their early to mid-20s, they become inured to "even the most violent" images. The effects of developing their sexuality largely divorced from real-life relationships are gradual and devastating. "It starts with lower reactions to porn sites, then there is a general drop in libido and in the end it becomes impossible to get an erection," Carlo Foresta, head of the Italian Society of Andrology and Sexual Medicine (SIAMS), told reporters. However, the condition is not irreversible and a proper recovery is possible within just a few short months.

Was it simply the compartmentalization of libido that caused the crash? If so, sex may feed, to a certain extent, on the messy complications of relationship with a real, not digitized, partner. Seemingly, this study would indicate that testosterone alone is not responsible for the male sex drive as the participants in this study were young and healthy with presumably normal hormone levels. What, though, is a normal testosterone level?

Generation T

Over a 17-year period ending in 2004, levels of testosterone in men were shown to be falling, a study finds. The reasons for a decline are unclear as neither aging nor changes in certain health factors, such as obesity or smoking, can completely explain the phenomenon.

"Male serum testosterone levels appear to vary by generation, even after age is taken into account," said Thomas G. Travison, Ph.D., of the New England Research Institutes and lead author of the study. "In 1988, men who were 50 years old had higher serum testosterone concentrations than did comparable 50-year-old men in 1996. This suggests that some factor other than age may be contributing to the observed declines in testosterone over time."

The study involved collecting blood samples as well as health and biographical data from approximately 1,500 randomly selected men residing in the greater Boston area. The researchers pointed out that, although subjects' general health was considered as part of the analysis, it is impossible to account for health or environmental influences that may have impacted the subjects' testosterone levels prior to enrolling in the study.

 

Sources: Wittert G, et al. Low testosterone is not a natural result of aging. Endocrine News. 2012.

Travison TG, Araujo AB, O'Donnell AB, Kupelian V, McKinlay JB. A Population-Level Decline in Serum Testosterone Levels in American Men. Journal of Clinical Endocrinology and Metabolism. 2007.