Obesity Can Have Negative Impact on Fertility in Both Men & Women

Many of the negative health effects of obesity, such as hypertension, heart disease, diabetes, and some types of cancers, have been extensively documented and widely publicized. But it may come as a surprise to some to discover that being significantly overweight can also impair a person's ability to reproduce.

In women, obesity has been linked to a reduced capacity to conceive and an increased likelihood of experiencing multiple miscarriages, while in men the condition has been found to decrease sperm count and exacerbate hormonal changes that can result in infertility.

"Obesity is a major health problem that is associated with infertility and miscarriage," Dr. Clarissa Gracia, a reproductive endocrinologist, wrote in an Oct. 24, 2006 article on the MSNBC website.

Thankfully, the news isn't all bad. In the same MSNBC article, Dr. Garcia noted that many weight-related fertility problems are reversible. "Weight loss is extremely valuable in the management of such patients and can enhance fertility and decrease miscarriage rates," she wrote.

Obesity and Male Infertility
The most current research into the link between obesity and male infertility was conducted by Dr. Eric M. Pauli and colleagues at Pennsylvania State University College of Medicine. The Pauli study, which appeared in the August 2008 edition of the journal Fertility and Sterility, found that obese men who were otherwise healthy were both less likely to have fathered a child and more likely to show signs of hormonal irregularities that indicate an impaired ability to procreate.

As described in a Sept. 16, 2008 article on the Reuters news service website, Pauli's findings indicate that obesity can directly and indirectly affect male fertility in a number of ways:

Compared with their thinner counterparts, obese men had lower levels of testosterone in their blood, as well as lower levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) -- both essential to reproduction. ...

Of the 87 men in the study, 68 percent had had a child. Pauli's team found that the average body mass index, or BMI, was lower among these men compared with those who'd never fathered a child; in the former group, the average BMI was 28, which falls into the range for "overweight," while the average BMI for childless men was nearly 32, which falls into the "obese" range. ...

Past studies have linked obesity with a dampened libido and increased risk of erectile dysfunction, the researchers note. Those effects, they say, along with the hormonal alterations seen in this study, could act together to decrease an obese man's fertility.

Research into the relationship between male obesity and infertility is a relatively recent phenomenon. Two years prior to the publication of the Pauli study, scientists with the National Institute of Environmental Health Sciences (NIEHS) announced what participating researcher Markku Sallmen referred to as "the first study to examine male BMI and couple fertility." The NIEHS study, which appeared in the September 2006 edition of the journal Epidemiology, involved a survey of 2,111 couples in Iowa and North Carolina.

In her Sept. 1, 2006 article for WebMD Health News, writer Miranda Hitti reported that the NIEHS researchers had discovered a significant correlation between an increased BMI and a decreased likelihood of having children:

Compared with men with normal BMI of 20-22, those who had a three-point increase in BMI were 10 percent more likely to be a partner in an infertile couple during the four-year study period.

"The results were the same when we limited the analysis to couples with female BMI of less than 26," Sallmen tells WebMD.

"I think that this finding offers further support for the idea that men's BMI is an independent risk factor for infertility," Sallmen adds.

Obesity and Female Infertility
Among women, obesity has a much longer history of scientific association with an inability to conceive - but researchers have recently revealed new reasons for weight's impact on would-be mothers.

For years, obesity has been associated with disrupted or nonexistent ovulation, which obviously renders a woman incapable of becoming pregnant. But it wasn't until 2007 that Dutch scientists established a correlation between obesity and infertility in women who continued to ovulate.

Published in the December 2007 edition of the journal Human Reproduction, a study led by Dr. Jan Willem van der Steeg of the Academic Medical Center (AMC) in Amsterdam, The Netherlands, found that obese women who continued to ovulate were nonetheless significantly less likely to conceive than were women with lower BMIs.

According to a Dec. 11, 2007 WebMD Health News article by Salynn Boyles, the AMC study charted more than 3,000 couples who had been unable to conceive for at least a year. Tracking the couples until they either achieved pregnancy or entered fertility treatment, the researchers determined that women with a BMI of 35 to 39 were 26 percent less likely to conceive than were women of normal body weight. Women whose BMI increased to 40 or higher were 43 percent less likely to become pregnant.

"We thought that if a woman's obesity was not affecting her ovulatory function, her fertility would be similar to a normal-weight woman's," reproductive endocrinologist Dr. William Dodson told Boyles. "But this does not appear to be true."

Miscarriage and Other Complications
Even when overweight or obese women are able to become pregnant, their weight can continue to have a negative influence.

A Sept. 20, 2008 article on the Irish Health website reported on a study in the United Kingdom that found a link between high maternal BMI and multiple miscarriages. An analysis of 700 women who had suffered three or more miscarriages revealed that 45 percent of the women had been overweight or obese while pregnant.

Of the subjects who later became pregnant again, the article reported, obese women accounted for19 percent of those who miscarried again, but only 11 percent of the women who gave birth.

"Ours is the first study to look directly at the link between BMI and recurrent miscarriage," Winnie Lo of St Mary's Hospital in London said. "[The study] shows that obese women who experience recurrent miscarriage are at greater risk of subsequent pregnancy loss."

In addition to miscarriages, a Sept. 20, 2005 Associated Press article listed other obesity-related risks which obese women and their children face a greater likelihood of developing:

  • Being obese can double a pregnant woman's chances of developing gestational diabetes or a pre-eclampsia (a potentially life-threatening condition marked by hypertension and the presence of elevated levels of protein in the mother's urine).
  • Maternal obesity also doubles the baby's risk of developing a neural tube birth defect such as spina bifida (an incompletely developed spinal cord which is accompanied by nerve damage).
  • The more overweight a woman is, the more likely she'll be forced to give birth by caesarean section. As a woman's weight increases, though, so do C-section risks such as excessive blood loss and infections.
  • Excess weight even makes it difficult to estimate the fetus' weight, track its heart rate, or administer an epidural or other anesthesia during labor.

Getting Help
As Dr. Clarissa Gracia indicated in her article, the good news about the connections between obesity and infertility is that many of the risks and problems can be reduced or eliminated by losing the excess weight.

Online, a wealth of websites, such as Obesity Treatment, Weight Loss Central, and the Weight Loss Help Directory, offer information about how to lose weight safely and effectively. For individuals who require professional assistance to overcome their weight-related challenges, programs such as Structure House and the Wellspring network of weight loss camps and schools offer the opportunity to work with some of the field's premiere practitioners.