One or more sugary drink a day – by either partner – can ruin a couple's chances of having a baby.

Researchers at the Boston University School of Public Health said: '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.'

Lead author Elizabeth Hatch, professor of epidemiology, added: '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% of couples in the States 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.

The researchers surveyed 3,828 women aged 21 to 45 living in the US 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% reduced fecundability, the average monthly probability of conception.

Females who consumed at least one fizzy drink per day had 25% lower fecundability; male consumption was associated with 33% 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 drinks 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.