age related changes to testosterone level

Andropause and low testosterone

It is helpful to define andropause in terms that relate to low testosterone levels in men regardless of age. One doctor in a recent journal article defined it as "a decline in serum (blood) testosterone in older men to levels below the normal range for young men, with associated clinical manifestations consistent with androgen deficiency."¹

Aging in men is associated with a one percent decline in total testosterone level each year starting at around age forty. About twenty percent of men in their sixties and fifty percent of men in their eighties have a testosterone level significantly below normal. Men who develop a serious illness, take certain kinds of medications, or who don't eat a healthy variety of foods are even more likely to have low testosterone levels. Furthermore, about one in three men with symptoms of andropause turn out to have a testosterone level lower than normal². Many of these men will simply feel better when their testosterone level is raised through hormone replacement therapy.

Decrease in available testosterone vs total testosterone

The relationship between testosterone and SHBG has confused many who question the existence of andropause as a legitimate syndrome. They have argued that the level of total testosterone as measured in blood falls only slightly up to the age of 70. This is true. Yet, the level of SHBG tends to increase with aging. At any time, approximately 98 percent of circulating testosterone is bound to SHBG, which leaves only 1-2 percent available for use by cells. If SHBG levels increase with age while testosterone production decreases, the amount of available testosterone is actually decreasing at a faster rate than total testosterone.

Cause of age-related low testosterone

The age-related decline in testosterone production is due to many factors that produce a gradual downward spiral:

The number of Leydig cells declines.
The existing Leydig cells produce less testosterone.
Less testosterone is secreted into the bloodstream by the testes in response to LH.
The hypothalamus secretes less gonadotropin-releasing hormone.
As a result, production of LH by the pituitary gland decreases and less testosterone production is demanded of the testes.

Aging also may change the daily cycle of testosterone production. In young men, peak testosterone delivery occurs in the morning. As men age, the testosterone level becomes increasingly more constant throughout the day and night.

This simplified view of age-related changes to testosterone levels leads to questions about the actual effects the decreasing level has on the body, mind and emotions of the aging male. By no means does the decline in testosterone account for all of these changes but it certainly plays a significant role.

Physical symptoms of low testosterone include:

Poor or no erections
Decline in sexual activity
Loss of muscle mass and strength
Loss of bone mass that can lead to osteoporosis
Fatigue and loss of energy
Reduction in body hair and skin thickness
Development of hair in ears and nose
Increase in upper and central body fat
Increase in heart and artery disease
Problems with circulation
Sleep disturbances

Mental symptoms of low testosterone include:

Decreased intellectual ability
Memory loss

Emotional symptoms of low testosterone include:

Loss of interest in sex
Depression
Irritability
Loss of sense of well-being

Each individual may experience a different number and type of symptoms. Some symptoms of low testosterone may be clearly related to other physical and mental illnesses or even to such poor habits as smoking, drinking too much alcohol or overeating. Before assuming that testosterone supplementation is necessary to feel better, you and your doctor will want to run through a variety of diagnostic steps to pinpoint specific causes of your symptoms and a full range of behavioral and other changes that might help you feel better.

References

Brawer, Michael K., MD. Androgen Supplementation and Prostate Cancer Risk: Strategies for Pretherapy Assessment and Monitoring. Rev.Urol. 2003;5 (suppl 1):S29-S33.

Caruthers, Malcolm, MD. The Testosterone Revolution. London: Thorsons; 2001

Heaton, Jeremy, P.W., MD. Hormone Treatments and Preventive Strategies in the Aging Male: Whom and When to Treat? Rev.Urol. 2003;5(suppl 1):S16-S21.

Matsumoto, Alvin M., MD. Fundamental Aspects of Hypogonadism in the Aging Male. Rev.Urol. 2003;5(suppl 1):S3-S10.

McCulloch, Andrew, MD. Case Scenarios in Androgen Deficiency. Rev.Urol. 2003;5(suppl 1):S41-S48.

Nieschlag, E., Behre, H.M., Nieschlag, S. Testosterone: Action, Deficiency, Substitution. Berlin: 1998.

Steidle, Christopher P., MD. New Advances in the Treatment of Hypogonadism in the Aging Male. Rev.Urol. 2003;5(suppl 1):S34-S40.

Notes

1. Matsumoto, Alvin M. Fundamental Aspects of Hypogonadism in the Aging Male. Urology. Vol. 5, Supplement 1. 2003;S3-10.

2. Morley, JE. J Gend Specif Med. 2001;4:49-53.

Posted February 2004
Updated August 2009

Next article in this series: diagnosing testosterone