THE BLOG
05/04/2010 05:12 am ET Updated Nov 17, 2011

Testosterone: Friend Or Foe?

He's a guy. They don't talk, they fight. It's all that crazy testosterone.

- Kim Cattrall as Samantha Jones on Sex in the City

If testosterone is responsible for all of the negative behaviors among men, wouldn't that mean that men with lower levels are healthier than those with normal or high levels of testosterone?

Most people know that testosterone (T) is responsible for sexual development in men and is important for libido and sexual function. However hormones, by definition, have effects throughout the body. There are testosterone receptors in nearly all tissues in the body, so this primary male hormone impacts nearly every organ system. We know that testosterone impacts hair growth in some areas (face, chest) and loss in others (scalp). It is also especially important in muscle and bone growth, impacts cardiac function and affects the central nervous system. Truth be told, it is linked to behaviors such as aggression, risk-taking and territoriality.

As a counter-point, the central nervous system effects of testosterone are not all negative. Testosterone has positive effects on mood, energy levels, feelings of well-being and vitality. Low T is associated with depression and with poor brain function on tests of memory and comprehension. Testosterone also has been shown to be an important anti-oxidant, protecting nerve cells against oxidative damage. In fact, low levels may make diseases like Alzheimer's worse.

Most testosterone is produced in the testes with stimulation from hormones secreted by the hypothalamus (GnRH) and pituitary glands (LH). The adrenal gland also produces some testosterone as well as other androgens (male hormones) such as DHEA. These other androgens are also important for libido and energy.

More and more, we are finding low T in our male patients. This does not appear to be only because we are checking levels more often. A large study showed that average T levels have fallen from 1987 to 2007. Among 1,532 randomly selected men at three time periods between those years, there was a slow, steady decline in T levels such that a 65 year old in 2007 had 15 percent lower T than a 65-year-old in 1987 -- even correcting for being over weight or smoking.

Symptoms of low Testosterone
Low libido
Decreased morning erections
Low energy or fatigue
Depressed mood
Irritability
Osteoporosis
Shrinking testicles
Loss of muscle mass or failure to gain muscle despite working out

Low testosterone may be caused by diseases of the hypothalamus, pituitary gland or testicles. Usually, however, low levels are the result of a natural decline with age (after the age of 40 or so) and/or lifestyle factors such as stress, physical inactivity, chronic illness, poor sleep or substance abuse (including tobacco and alcohol). To some degree this decrease in testosterone due to stress is evolutionary. The body's production of sex hormones is exquisitely sensitive to stress - be it physical or emotional. Testosterone in men drops in the face of chronic stress or anxiety, partly because the primal role of the sex hormone system is to drive reproduction. If the body senses an inability to care for itself, the last thing it wants is to produce a child needing to be taken care of in the face of such external stress. This system can't differentiate attack by tigers from the daily grind in an unhappy job - it is all translated chemically in the body and ends in low testosterone production.

Coming back to the initial question - is it better for men to have low T so that they will talk more and fight less? Unfortunately, such a trade-off has its cost.

Cardiovascular disease is the number one killer in men in the United States. Men with subnormal T levels have higher cholesterol and an increased risk of diabetes, both of which are significant risk factors for heart disease. Obesity also increases the risk for diabetes and heart disease, and men with low T have more body fat. In fact, the obesity-low T link manifests as a vicious cycle. Body fat causes an increase in the conversion of testosterone into estrogen - yes, men have estrogen. In fact, a 50-year-old man has, on average, more estrogen than a post-menopausal 50-year-old woman. The more T that gets converted, the lower is the ratio of testosterone to estrogen and the more muscle mass is lost and fat is gained. This gets to be self-perpetuating.

So, it appears that while testosterone is associated with riskier health behaviors, low T is associated with serious diseases like osteoporosis, Alzheimer's, depression, diabetes and heart disease. Therefore it is unhealthy to leave low T untreated. While elevating levels of T above physiologic levels, as is done by some body builders and athletes, has been associated with enlarged hearts (cardiomyopathy) and higher risk of heart attacks, high blood pressure and stroke, replacing low testosterone to achieve normal values has not been associated with such negative outcomes.

Men over 40 should have their levels of testosterone checked regularly, especially if they are experiencing any of the symptoms listed above. That level may be as important to overall health as cholesterol number or blood pressure. There are many proven ways to treat low T, under a doctor's supervision. Testosterone may make us fight more and talk less, but it also keeps us going in many healthy ways.

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