Study: Body mass affects sperm quality
PHILADELPHIA, Pennsylvania (AP) -- Beer bellies may take a toll on men
below the belt, not just around it.
Men who weigh too much are more likely to have poor sperm quality, research
on nearly 1,600 young Danish men has found. Being too thin is a problem,
too.
Women don't get off the hook. Though it's long been known that very
overweight women have trouble conceiving naturally, a large new study
confirms they also are less likely to become pregnant even when embryos are
fertilized in lab dishes and placed in their wombs.
"Among the severely obese, we saw significantly reduced implantation and
pregnancy rates," said Dr. David Ryley of Beth Israel Deaconess Medical
Center in Boston. He presented results of the women's study this week at a
meeting of the American Society for Reproductive Medicine.
The sperm study was done by doctors at various hospitals and universities
in Denmark and published in the October issue of the reproductive society's
journal, Fertility & Sterility.
It involved 1,558 men, average age 19, who volunteered to give a semen
sample during mandatory exams to determine their fitness for military
service in two cities, Amsterdam and Aalborg.
Sperm counts, sperm concentration, semen volume and other measures of sperm
quality such as shape and motility were measured, along with testicle size
and hormone levels. Researchers also calculated each man's body mass index,
a measure of obesity that takes into account height and weight.
Scores for men with healthy BMIs -- between 20 and 25, or 139 to 174 pounds
for a man who is 5-foot-10 -- were compared to those of men above and below
that range.
Sperm counts and sperm concentration were 28.1 percent and 36.4 percent
lower respectively in underweight men. The same measures were 21.6 percent
and 23.9 percent lower respectively in overweight men.
Why this may be happening is unclear.
"Low BMI can result from a 'healthy lifestyle' but may also be due to many
chronic diseases," the authors write.
The biological explanation or mechanism also may be different in
underweight and overweight men, they note.
"It may be an alteration in hormonal values," said Dr. Anthony J. Thomas
Jr., a Cleveland Clinic urologist who is president of the Society for Male
Reproduction and Urology and was not involved in the study.
Men produce and need a certain amount of the female hormone estrogen. Fat
cells produce estrogen, so too much or too little of it may be a problem.
"There's a balance, and that balance is the milieu in which sperm
develops," Anthony said.
Other research suggests that smoking and heavy alcohol use also harm sperm
production, he said. The new study is a reminder that doctors should always
check a man for signs of infertility when couples are having trouble
getting pregnant because the problem is just as likely to involve men as
women.
"It's not uncommon for a man to come in after his wife has had a million
tests" and then discovered to have sperm problems, Thomas said. "It's
probably one of the first things a doctor should do."
The other study on women involved 5,847 attempts at in vitro fertilization
in which embryos are fertilized in a lab dish, at Beth Israel's infertility
clinic, Boston IVF.
Obese women -- whose BMIs were 35 and over -- had little more than a 1 in 5
chance of becoming pregnant through IVF; the odds were better than 1 in 4
for women with healthy weights. Embryos were also less likely to implant in
the fat women.
Overweight women have irregular periods and lower ovulation rates, making
it harder for them to get pregnant naturally, Ryley said. When given
fertility treatments, they often need higher doses of drugs and for a
longer time to spur ovulation, he said.
His study didn't find that very thin women had more trouble conceiving as
some previous research has suggested.