Brain damage from heading a football may be five times more extensive in women than men, a US study on Tuesday based on nearly 100 amateur players, AFP reports.

The report in the journal Radiology suggested that sex-specific guidelines may be needed to guard against head injuries in football.

For the study, 49 male and 49 female players were given a form of MRI called diffusion tensor imaging, which analyzes the health of the brain’s white matter by looking at water balance in the tissue.

Players’ ages ranged from 18-50, and both groups reported a similar number of headings over the previous year. Men reported an average of 487 headings and women 469.

The scans showed that “the volume of damaged white matter in women soccer players was five times greater than for male players,” according to the report.

The women had eight brain regions where white matter – which involves communication between different parts of the brain – were affected, compared to three in men.

Researchers said the brain changes were “subclinical,” meaning the players did not report any altered thinking ability.