|Obesity in Men Linked to Infertility
Men with increased body mass index (BMI) were significantly more likely to
be infertile than normal-weight men, according to research conducted at the National
Institute of Environmental Health Sciences (NIEHS), one of the National Institutes
“The data suggest that a 20-pound increase in men’s weight may increase the
chance of infertility by about 10 percent,” says Markku Sallmen, lead author
on the paper who is now at the Finnish Institute of Occupational Health. BMI
is a number calculated from a person’s weight and height. BMI provides a reliable
indicator of body fatness for most people and is used to screen for weight categories
that may lead to health problems.
The researchers studied couples enrolled in the Agricultural Health Study (AHS),
a large project that began in 1993 examining factors that impact the health of
farmers and their families in agricultural communities.
“Women who are overweight or obese tend to have a more difficult time becoming
pregnant than normal-weight women, but whether men who are overweight or obese
also have fertility problems had not been studied,” says Donna Baird, Ph.D.,
an NIEHS epidemiologist with the study. The study is published in the September
2006 issue of Epidemiology.
The data on infertility and body mass came from questionnaires that 1,468 farmers
and their wives completed when they enrolled in the study. The wives completed
a family health questionnaire, which included information about the couple’s
reproductive history. The men reported their weight and height on a questionnaire
about their health. The analysis was limited to couples with a pregnancy attempt
during the four years before enrollment, and to women under the age of 40.
The researchers divided the couples into infertile and fertile groups. The infertile
couples were those that tried for longer than a year to conceive, and the fertile
couples were those that conceived within a year. The majority of men and women
were more than 30 years old. Twenty-eight percent of the couples had experienced
Researchers found that men’s BMI was an independent risk factor for infertility.
The researchers adjusted for other factors that could affect fertility, including
high BMI of the woman, age, cigarette smoking, alcohol intake, and solvent and
pesticide exposure. After adjustment, there was a general increase in infertility
with increased BMI, reaching a nearly 2-fold increase among obese men.
When researchers divided the sample into two equal groups by men’s age, they
found that men’s BMI was a risk factor for infertility in both the older and
The researchers did not have data on frequency of sexual intercourse, so it
is possible that overweight men have less sexual intercourse than their normal
weight counterparts and this could influence fertility. However, there have been
recent studies looking at semen characteristics that show lower semen quality
for overweight and obese men, as well as hormonal differences.
“This study provides data on some additional health problems associated with
obesity,” said David A. Schwartz, M.D., director of the National Institute of
Environmental Health Sciences. “Preventing obesity can help improve men’s overall
health, perhaps even their reproductive health.”
The NIEHS unveiled a new strategic plan, "New Frontiers in Environmental Sciences
and Human Health,” in May aimed at challenging and energizing the scientific
community to use environmental health sciences to understand the causes of disease
and to improve human health. The plan can be accessed at http://www.niehs.nih.gov/external/plan2006.
The ongoing Agricultural Health Study (AHS) is funded by the National Institute
of Environmental Health Sciences and the National Cancer Institute, two of the
National Institutes of Health, and the Environmental Protection Agency. The AHS
(http://www.aghealth.org/) is designed to investigate the effects of environmental,
occupational, dietary, and genetic factors on the health of the agricultural
population. It is composed of certified pesticide applicators and their spouses
in Iowa and North Carolina. The study will provide information that agricultural
workers can use in making decisions about their health and the health of their
The National Institute of Environmental Health Sciences (NIEHS), a component
of the National Institutes of Health, supports research to understand the effects
of the environment on human health. For more information on environmental health
topics, please visit our website at http://www.niehs.nih.gov/.
The National Institutes of Health (NIH) — The Nation's Medical Research
Agency — includes 27 Institutes and Centers and is a component of
the U.S. Department of Health and Human Services. It is the primary federal
agency for conducting and supporting basic, clinical and translational medical
research, and it investigates the causes, treatments, and cures for both common
and rare diseases. For more information about NIH and its programs, visit www.nih.gov.