Men who start families later in life should be aware of the potential health risks to their children, according to US doctors who found that babies born to older fathers tend to have more medical issues than those born to younger men.

Researchers at Stanford University in California studied health records linked to all live births in the US between 2007 and 2016, amounting to more than 40 million babies. The records showed that children born to men aged 45 and over had a 14% greater risk of premature birth, low birth weight and being admitted to neonatal intensive care compared with babies born to younger fathers.

Infants born to men aged 45 and over also scored lower on the Apgar newborn health test, and were 18% more likely to have seizures compared with infants born to fathers aged 25 to 34 years, according to the study in the British Medical Journal. For women, the risk of gestational diabetes was greater when they had children with older men.

Michael Eisenberg, a senior author on the report, said that while the increased risks were modest, couples should not ignore the father’s age when it came to family planning. “This is something else to take into consideration,” he said. “There are potential risks with waiting. Men should not think that they have an unlimited runway.”

But Eisenberg stressed that the increased risks for individuals were small. After adjusting for the mother’s age and other factors such as education and whether she smoked, he found that children born to men aged 45 and over were born less than a day earlier on average, and weighed only 20g lighter (just over half an ounce) than those with younger fathers.

More important, said Eisenberg, was the impact modest increases in health risks might have across populations as paternal age continues to rise. In England and Wales, the average age of first-time fathers has risen about a year per decade for the past 40 years, according to the Office of National Statistics.

“When I talk to couples about health risks, I use the lottery as an analogy,” Eisenberg said. “If you buy two tickets, your chances of winning double, but you are still unlikely to win. Even if your risk for something goes up 10-20%, the absolute risk for an individual doesn’t change that much.”

Eisenberg and his colleagues suggest changes in the DNA of older men’s sperm might explain their findings. The concern is backed up by previous work, including a Harvard study last year that found births through IVF fell as the fathers’ age increased.

In a commentary accompanying the BMJ study, Hilary Brown, a perinatal epidemiologist at the University of Toronto in Scarborough, cautioned that despite the researchers’ efforts, it was hard to disentangle the effects of the mother’s and father’s ages. And she warned that damage to DNA in older mens’ sperm was only one possible explanation for the effects.

“Studies have shown that advanced paternal age is associated with negative health behaviours such as smoking and frequent alcohol consumption, obesity, chronic disease, mental illness, and sub-fertility,” she writes, adding that all are linked to health problems in newborns.

• This article was amended on 2 November 2018. It previously said the researchers in California “studied health records linked to all live births in the state between 2007 and 2016, amounting to more than 40 million babies.” The study was in fact looking at births across the US, not just California.