Although most of a womans estrogen is manufactured in her ovaries, 30% is produced in fat cells by a process that transforms circulating adrenal male hormones into estrogen. Because a normal hormonal balance is essential for the process of conception, it is not surprising that extreme weight levels, either high or low, can contribute to infertility.

Being Overweight. Being overweight or obese (fat levels that are 10% to 15% above normal) can contribute to infertility in various ways. Obesity is highly associated with polycystic ovarian syndrome (PCOS), which is cause of infertility in some cases. In one 2003 study, overweight women without PCOS were classified in one of five grades, depending on the severity of the obesity. The risk for irregular or absent periods increased two-fold by each increase in grade. In this group, amenorrhea (absent periods) was also highly associated with type 2 diabetes and blood sugar abnormalities.

Being Underweight. Body fat levels 10% to 15% below normal can completely shut down the reproductive process. Women at risk include the following:

• Women with eating disorders, such as anorexia or bulimia.
• Women on very low-calorie or restrictive diets are at risk, especially if their periods are irregular.
• Strict vegetarians might have difficulties if they lack important nutrients, such as vitamin B12, zinc, iron, and folic acid.
• Marathon runners, dancers, and others who exercise very intensely. (Lower body fat contributes to menstrual irregularities in competitive athletes, but other mechanisms are also involved.)

Lifestyle Factors

Smoking. Women who smoke one or more packs a day and those who started smoking before the age of 18 are at greater risk for infertility. Smoking also increases the risk for still births and low birth-weight babies. Male smokers also endanger fertility. Men who smoke have poorer sperm quality than nonsmokers, and they also have lower sex drives and have sex less frequently than nonsmokers. Heavy marijuana smoking appears to adversely affect fertility in both males and females.

Caffeine. A correlation has been found between caffeine consumption and infertility, possibly because has estrogen-like effects. Caffeine is found not only in coffee but also in tea, many soft drinks, chocolate, and a number of common medications.

Alcohol. Even moderate alcohol intake (as little as five drinks a week) can impair conception and also have adverse effects on the developing fetus.

Vaginal Douching. Vaginal douching can impair fertility and cause a number of gynecological problems. Studies suggest that it may contribute to infection, pelvic inflammatory disease, low-birth weight babies, preterm birth, and tubal pregnancy.

Sexual Practices. Sexual practices such as having multiple partners, not using condoms, and having intercourse during a period increase the risk for sexually transmitted organisms that can cause pelvic inflammatory disease leading to infertility.