| NEW YORK
NEW YORK (Reuters Health) - A new study has found a
"substantial" drop in U.S. men's testosterone levels since the
1980s, but the reasons for the decline remain unclear. This
trend also does not appear to be related to age.
The average levels of the male hormone dropped by 1 percent
a year, Dr. Thomas Travison and colleagues from the New England
Research Institutes in Watertown, Massachusetts, found. This
means that, for example, a 65-year-old man in 2002 would have
testosterone levels 15 percent lower than those of a
65-year-old in 1987. This also means that a greater proportion
of men in 2002 would have had below-normal testosterone levels
than in 1987.
"The entire population is shifting somewhat downward we
think," Travison told Reuters Health. "We're counting on other
studies to confirm this."
Travison and his team analyzed data from the Massachusetts
Male Aging Study, a long-term investigation of aging in about
1,700 Boston-area men. Data from the men were collected for
three time intervals: 1987-1989, 1995-1997, and 2002-2004.
While a man's testosterone level will fall steadily as he
ages, the researchers observed a speedier decline in average
testosterone levels than would have been expected with aging
They hypothesized that the rising prevalence of obesity as
well as the sharp decline in cigarette smoking might help
explain their findings, given that testosterone levels are
lower among overweight people and smoking increases
testosterone levels. But these factors accounted for only a
small percentage of the observed difference.
It's likely that some sort of environmental exposure is
responsible for the testosterone decline, Travison said,
although he said attempting to explain what this might be based
on the current findings would be "pure conjecture."
The researchers used body mass index, the ratio of height
to weight, to estimate obesity levels, he noted, but this is
not a very accurate way to gauge the real adiposity, or fat
content of the body, so it's possible that obesity might be
more of a factor than it appears in this analysis.
"I think like most things that are complex, it's likely
that there is no one cause," he said.
SOURCE: Journal of Clinical Endocrinology and Metabolism,