Testosterone is the male sex hormone. The body produces the hormone only in the testes, where it is normally only present in very small amounts. It has a number of functions that have enabled our species to survive: it allows the male body to produce and secrete sperm, it regulates hair growth and courtship, and it is associated with other biological functions such as creating stress hormones and regulating immune system function. But in recent years, testosterone has also been touted as a major factor behind aggressive behaviour, as well as poor health and a short life span. In 1977, a study in Proceedings of the National Academy of Sciences reported that men who had low testosterone levels were more aggressive than men who had high levels.
Is testosterone supposed to make you more aggressive?
At the Institute of Cancer Research, London, Charles Swanton works with mice that have been engineered to lack any of the relevant genes. “You don’t have aggression and depressive-type behaviours,” he says. Instead, their brains are pre-programmed to prefer approach-avoidance strategies, avoiding predators and, as a result, being safer at home. Swanton says this is consistent with brain scans of people with more muscle mass. With more muscle, a person needs to use their arms less. For their brain to direct them into action without having to use their arms, their neural pathways must be strengthened. But, instead of being immediately driven towards battle, the neural pathways would have to be more easily redirected, into alternatives, the type of strategy employed by a hunter.
Side effects of too much testosterone
Testosterone is a hormone whose main role is to regulate male sexual function. But if men have an imbalance in this hormone, there can be negative side effects, including depression, fatigue, low libido and muscle weakness. The diagnosis of excess testosterone in a patient comes as a result of the laboratory analysis of circulating testosterone. An imbalance of this hormone can be measured using the medical test called the blood testosterone level test. This test is commonly used in prostate cancer patients.
Testosterone Replacement Therapy for Men
Ryan has lived with these side-effects since he was diagnosed. A decade ago, he had surgery to remove a tumour, and the next year he was diagnosed with prostate cancer. “That was a game-changer,” he says. Testosterone replacement therapy was on the horizon, and Ryan wondered if it would help. It has now become one of the most common treatments for prostate cancer. According to the US Food and Drug Administration, more than 400,000 American men received testosterone therapy in 2013. About half of those are over 55; over two-thirds are white men. Overall, however, the numbers are a drop in the ocean: There are 2.6 million US men over the age of 40 and only about one in eight men will develop prostate cancer.
As the rest of us age, our ability to build and maintain muscle mass, and especially to expend energy, declines. The secret to a long and healthy life, according to Mark Mattson, director of the National Institute on Aging’s Neurodegenerative Disease Research Program, is to keep a diverse diet, stick to an active lifestyle and take care of our bodies as we age. “Men should avoid high-protein diets,” he says. “Be moderate in alcohol, and consume a proper diet.” Mattson says men need a “cocktail” of lifestyle factors, including increased physical activity and a normal body weight, to maximise their odds of avoiding disease. They also need to keep their testosterone levels in check.