TUESDAY, Nov. 5, 2002 (HealthDayNews) -- The hormone that makes men male may also play a big role in keeping them sharp into old age.
Older men who had high levels of testosterone freely circulating in their blood performed better on memory and cognitive tests than men with lower testosterone levels, a new study found.
"What it's suggesting is that higher testosterone may preserve memory and other specific aspects of cognition," says Susan Resnick, study co-author and an investigator in the National Institute on Aging's Laboratory of Personality and Cognition. "Still, this is not a causal relationship. It's an association. It's too early to tell men to take testosterone to improve memory."
Using data from the Baltimore Longitudinal Study of Aging, the longest-running examination of human aging, researchers over a 10-year period analyzed the free, or unbound, testosterone circulating in the bloodstreams of 407 men who were between 50 and 91 years old. The free testosterone levels were then correlated with the men's performances on a series of memory and cognitive tests.
Why was free testosterone the focus of the study?
Most testosterone made by the body becomes bound to a protein called sex hormone binding globulin (SHBG), Resnick says. However, about 2 percent circulates freely through the blood.
Free testosterone can pass through the blood-brain barrier, while bound testosterone cannot, Resnick adds. "The free testosterone is what can get into the brain and have an effect of behavior and cognition," she explains.
Researchers found the higher the level of free testosterone, the better men performed on the memory and cognitive tasks. Among the tests given:
- The men were shown images of complex geometric shapes and asked to choose the mirror image of each from among several possibilities. This test measured "spatial rotational ability," or how well the men were able to visualize rotating objects on a page, Resnick says.
- They were asked to name as many words as they could think of beginning with a certain letter. They were also asked to name all the synonyms they could think of for a particular word.
- They were shown a "shopping list" and then had to recall as many items on the list as they could.
- They were shown a geometric image and then had to recall the image and draw it.
"The biggest and most consistent effects were on the two memory tests," Resnick says.
The study appears in the November issue of the Journal of Clinical Endocrinology & Metabolism.
Dr. Abraham Kryger, medical director of the Monterey Preventive Medical Clinic in California, says he wasn't surprised by the findings.
"It's common knowledge among endocrinologists that higher levels of free testosterone improve memory and cognition," Kryger says.
Testosterone is produced in the testes, the male reproductive glands that also produce sperm. It's essential in the development and maintenance of many male characteristics, including the penis and testes, facial and body hair, muscle mass and strength, deepening of the voice and sex drive.
As men age, their testes tend to produce less testosterone than they did during adolescence and early adulthood, when testosterone production peaks. Blood levels of SHBG also increase with age, meaning older men may also have a higher percentage of bound testosterone.
Men with low levels of free testosterone in their blood can be prescribed testosterone replacement, which comes in injectable, patch or gel form, Kryger says.
Symptoms of low testosterone include fatigue, development of breasts, loss of sex drive and problems with erections, he says.
If men suspect they could have low testosterone levels, they should see a doctor. Men need to make sure the doctor checks their level of free testosterone, not just total testosterone, he says.
Testosterone is an anabolic steroid with the potential for abuse. Body builders and athletes who abuse testosterone take from 100 to 1,000 times the amount that a man prescribed testosterone replacement would take, Kryger says.
Resnick cautions men against rushing out and demanding testosterone replacement from their doctors. Some studies suggest supplements might trigger excessive red blood cell production, causing a thickening of the blood and increasing the chance of stroke, she says.
If you already have adequate levels of testosterone, taking too much can cause a suppression of your body's own production of it, she adds.
"We still have much to learn," Resnick says. "Until we know much more about the fundamental effects of sex hormones on the aging brain and other parts of the body, testosterone supplementation is not a prudent choice for older men seeking to improve their memory and cognitive performance."
What To Do
Read more about testosterone's role in the body at The Hormone Foundation. For more on the natural decline of testosterone, read this.
