As men age, the level of testosterone in their blood decreases, sometimes dramatically. So, researchers looked at replacing testosterone in hopes of slowing the signs of aging.

Low testosterone can be linked to loss of strength and mental function, lower bone mass and increased fat.

"With this study, we want to investigate if it was possible with the testosterone to prevent the signs of and symptoms of aging," said Dr. Marielle Emmelot-Vonk, of University Medical Center in Utrecht, The Netherlands.

Emmelot-Vonk was among the researchers who studied 230 men ages 60 and 80 over a six-month period. Half received daily testosterone supplements.

"The fat mass in the body decreased and the lean mass increased, and also the insulin sensitivity improved a bit," researcher Yvonne van der Schouw said.

The findings of the research, which appear in the Journal of the American Medical Association, also showed no change in the harmful intra-abdominal fat, and levels of HDL – good cholesterol – went down in the men taking the supplements. No other improvements were reported.

The researchers didn't recommend testosterone supplements. Rather, they said men should look to diet and exercise to fight the effects of aging.

"It is important that you eat healthy food, and it's important that you do a lot of activity," Emmelot-Vonk said.

Her father, 65-year-old Henk Vonk, said he wished taking testosterone had been the answer for aging. He said he can tell that his testosterone levels have gone down over time.

"I'm not so strong and fast anymore," Vonk said. "To be healthy, I make a walk every day, and I go to the gym."