Couples with high cholesterol have more difficulty conceiving than those with normal levels of the substance in their blood, researchers reported Tuesday, in what they called the first study to link fertility difficulties to the fat molecule commonly associated with cardiovascular problems.
In a study of 501 couples who were trying to conceive, the time it took for the woman to become pregnant was longest if both partners had high cholesterol. When the woman alone had high cholesterol, pregnancy was also delayed. A man with high cholesterol did not significantly delay pregnancy if the woman's cholesterol reading was within the normal range, according to the study, conducted by the National Institutes of Health, the University at Buffalo and Emory University in Atlanta.
Cholesterol is critical to the production of hormones such as estrogen in women and testosterone in men, as well as sperm, said Enrique Schisterman, chief of the epidemiology branch of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, who led the study. Too much or too little cholesterol can interfere with that process, he said.
"We need optimal amounts," Schisterman said. "An excess sometimes creates an imbalance of too much hormones, or too little hormones. You have to have a sweet spot."
In addition to the link between cholesterol and fertility, Schisterman noted that the male's role in conception difficulties is noteworthy. Both partners who want to have children should focus on living healthy lifestyles and keeping cholesterol levels down, said Schisterman, who devoted his career to fertility research after he and his wife struggled to have children. They have one child born through in vitro fertilization and another who is adopted, he said.
The study, published online in the Journal of Clinical Endocrinology and Metabolism, should not be interpreted to mean that couples seeking to conceive should take common medications such as Lipitor that lower cholesterol, Schisterman said. The researchers did not look at interventions, he said.
Measures of overall cholesterol, high-density lipoproteins (HDLs), low-density lipoproteins (LDLs), and triglycerides that people are accustomed to receiving from their doctors were not used in the study. The researchers examined free cholesterol in the blood with a different metric.
Schisterman said the link between cholesterol and fertility had never been measured because it is difficult to find a population of couples trying to conceive and follow them for an extended period of time. For this study, the researchers recruited couples in Texas and Michigan from 2005 to 2009, and followed them for a year or until they became pregnant. A few dropped out during the research.
Even when they controlled for other factors that have been associated with infertility in the past, such as a high body mass index, high cholesterol clearly proved to be an additional problem, Schisterman said.