The amount of added sugar in the American diet has increased dramatically over the last 50 years. Much of that increase comes from higher intake of sugar-sweetened beverages, which constitute approximately one-third of the total added sugar consumption in the American diet. While consumption of these beverages has been linked to weight gain, type 2 diabetes, early menstruation, and poor semen quality, few studies have directly investigated the relationship between sugary drinks and fertility.

Now, a new study led by Boston University School of Public Health (BUSPH) researchers has found that the intake of one or more sugar-sweetened beverages per day -- by either partner -- is associated with a decreased chance of getting pregnant.

The study was published in Epidemiology.

"We found positive associations between intake of sugar-sweetened beverages and lower fertility, which were consistent after controlling for many other factors, including obesity, caffeine intake, alcohol, smoking, and overall diet quality," says lead author Elizabeth Hatch, professor of epidemiology. "Couples planning a pregnancy might consider limiting their consumption of these beverages, especially because they are also related to other adverse health effects."

About 15 percent of couples in North America experience infertility. Identifying modifiable risk factors for infertility, including diet, could help couples conceive more quickly and reduce the psychological stress and financial hardship related to fertility treatments, which are associated with more than $5 billion in annual US healthcare costs.

Through the Pregnancy Study Online (PRESTO), an ongoing web-based prospective cohort study of North American couples, the researchers surveyed 3,828 women aged 21 to 45 living in the United States or Canada and 1,045 of their male partners. Participants completed a comprehensive baseline survey on medical history, lifestyle factors, and diet, including their intake of sugar-sweetened beverages. Female participants then completed a follow-up questionnaire every two months for up to 12 months or until pregnancy occurred.

Both female and male intake of sugar-sweetened beverages was associated with 20 percent reduced fecundability, the average monthly probability of conception. Females who consumed at least one soda per day had 25 percent lower fecundability; male consumption was associated with 33 percent lower fecundability. Intake of energy drinks was related to even larger reductions in fertility, although the results were based on small numbers of consumers. Little association was found between intake of fruit juices or diet sodas and fertility.

"Given the high levels of sugar-sweetened beverages consumed by reproductive-aged couples in North America, these findings could have important public health implications," the authors concluded.