March 16 Heavy men are more likely than
their peers with more normal weights to have low sperm counts or
no sperm production at all, a key way to measure fertility,
according to an international study.
But the review of past studies, which covered a combined
total of 10,000 men and appeared in the Archives of Internal
Medicine, can't prove that overweight or obese men will have
more trouble fathering a child.
"In general you expect that men with lower sperm counts will
have a greater frequency of difficulty conceiving than men with
higher sperm counts, but it's not completely straightforward,"
said Jorge Chavarro at the Harvard School of Public Health, part
of the collaborative group that put out the study.
How well sperm move, their shape and the quality of DNA they
carry matter too, Chavarro said -- but previous studies have
suggested some of those measures of sperm quality may be
affected by obesity as well.
For the new analysis, French researchers combined data from
14 studies that compared sperm count in samples from normal
weight, overweight and obese men, as well as data from their own
About one-quarter of the combined 10,000 men had a low sperm
count. In another analysis, just over 250 of almost 7,000 men
had no sperm in their ejaculate at all.
Overweight men were 11 percent more likely to have a low
sperm count and 39 percent more likely to have no sperm than
their normal-weight peers, according to calculations by
Sebastien Czernichow and colleagues at the Ambrose Pare
Obese men, on the other hand, were 42 percent more likely to
have a low sperm count than their normal-weight peers and 81
percent more likely to have sperm-free ejaculate.
The researchers proposed a number of different theories for
the findings including that male hormones may be converted into
estrogen in fat tissue, affecting sperm-making, or that more fat
in the hips and stomach could make the scrotum too hot.
The results don't prove that overweight and obese men will
have more fertility troubles, although you wouldn't expect men
who have no sperm at all to be fertile, Chavorro said.
It's possible that obesity itself isn't to blame. It could
be that in some men an underlying health condition causes them
to gain weight and affects their sperm, said Stephen Winters,
professor of Medicine and Chief of the Division of
Endocrinology, Metabolism and Diabetes at the University of
Because of that, researchers can't say for sure whether
heavy men could boost their sperm production by losing weight.
Czernichow told Reuters Health in an email that losing
weight improves fertility in women, but that there's not much
data in men - though small case reports have suggested
weight-loss surgery may actually have a negative effect on
A study late last year found that being overweight was tied
to a lower sperm concentration and lower motility.
The current report is not conclusive and the risks are "not
huge," said Winters, who wasn't involved in the study. But he
added that fertility trouble is one of the health risks of
"This appears to be yet another health outcome for which
maintaining a healthy weight appears to be important," Chavarro
told Reuters Health.
"It's not only about your cardiovascular disease risk, it's
not only about diabetes and some forms of cancer. Obesity also
seems to affect outcomes that may be manifested in younger men."
(Reporting from New York by Genevra Pittman at Reuters Health;
editing by Elaine Lies and Bob Tourtellotte)