WASHINGTON, May 20 (Xinhua) -- High cholesterol levels may impair fertility in couples trying to achieve a pregnancy, researchers at the U.S. National Institutes of Health (NIH) said Tuesday.
"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," first author Enrique Schisterman of the National Institute of Child Health and Human Development, part of the NIH, said in a statement.
Cholesterol is a waxy, fat-like substance found in all cells of the body. It's used to make a number of substances, including hormones and vitamin D. High blood cholesterol levels typically do not cause any signs or symptoms, but can increase the chances for heart disease.
For the current study, the researchers studied 501 couples who were not being treated for infertility but who were trying to conceive a child between 2005 and 2009.
The women taking part in the study ranged from 18 to 44 years of age, and the men were over 18. The couples were followed until pregnancy or for up to one year of trying.
Among the couples, 347 became pregnant over the course of the 12-month study. Fifty-four couples did not conceive a child. A hundred couples withdrew from the study, including some whose plans to have a child changed.
The researchers measured each prospective parent's cholesterol by testing a blood sample taken at the study's outset. Rather than measuring low-density lipoprotein, known as "bad" cholesterol and other cholesterol subtypes, the researchers measured the total and free amounts of cholesterol in the blood.
The researchers found that on average, those couples in which the female did not become pregnant during the study duration had the highest free cholesterol levels.
In general, high free cholesterol levels were correlated with longer times to pregnancy and lower fecundability odds ratios.
Couples in which each partner had a high cholesterol level took the longest time to reach pregnancy. Moreover, couples in which the woman had a high cholesterol level and the man did not also took longer to achieve pregnancy when compared to couples in which both partners had cholesterol levels in the acceptable range.
"Our results suggest that couples wishing to achieve pregnancy could improve their chances by first ensuring that their cholesterol levels are in an acceptable range," Schisterman said.
The findings were published in the U.S. Journal of Clinical Endocrinology & Metabolism.