High cholesterol levels may be linked to infertility in both men and women

A new study finds a couple may have difficulty conceiving a child if both the man and woman have high cholesterol levels.

The study, which was published today in JCEM, The Journal of Clinical Endocrinology and Metabolism, also found that if only the woman has high cholesterol, the couple may still have difficulty having a child, compared to couple with both a man and woman with cholesterol levels in normal range.

The authors of the study suggest that cholesterol levels may impact fertility because the body uses the substance to regulate sex hormones such as testosterone and estrogen.

"From our data, it would appear that high cholesterol levels not only increase the risk for cardiovascular disease, but also reduce couples' chances of pregnancy," said Dr. Enrique Schisterman, chief of the Epidemiology Branch at the Eunice Kennedy Shriver National Institute of Child Health and Human Development at the National Institutes of Health, in a press release.

For the study, researchers at the NIH, the University of Buffalo and Emory University studied 501 couples from 2005 to 2009. The men and women were part of the Longitudinal Investigation of Fertility and the Environment, a year-long study designed to examine the impact environmental and lifestyle factors on the health and fertility of couples.

All of the couples were trying to achieve pregnancy but were not undergoing fertility treatments. Women's ages ranged from 18 too 44 years old, while all men were over age 18. The couples all lived in Michigan or Texas.

Study participants provided blood samples, which the researchers tested for cholesterol levels, including HDL cholesterol, LDL cholesterol and triglycerides.

With a mathematical formula, known as the "fecundability odds ratio," the researchers calculated the likelihood the couple would get pregnant and how long it might take.

The researchers found, on average, the females who did not become pregnant during the duration of the study tended to have the highest free cholesterol levels. In general, high free cholesterol was associated with more difficulty getting pregnant and lower levels of fertility. Additionally, if the woman had a higher free cholesterol level and the man had levels within average range, the couple still took longer to conceive than a couple with both a man and woman with acceptable ranges. The researchers also observed that Hispanic men had the highest free cholesterol levels.

High free cholesterol levels indicate an unhealthy balance between HDL (good cholesterol) versus LDL (bad cholesterol).

The researchers say their paper backs up prior studies that found cholesterol levels impact semen quality and increase risk for fertility-related problems in women, such as polycystic ovarian syndrome.

According to the researchers, infertility currently impacts 15 percent of reproductive-aged men and 17 percent reproductive-aged women in the U.S. The authors point out that as the rates of obesity continue to rise in the U.S., so too will the rates of infertility.