Researchers at the University of Texas (UT) scanned obituaries and high school yearbooks of 2,566 individuals whose brain autopsies are a part of the Mayo Clinic Tissue Registry.

The study focused on a variety of contact sports: baseball, basketball, boxing, football, hockey, lacrosse, soccer and wrestling; while non-contact sports such as tennis and golf were excluded.

This analysis identified 300 former athletes and 450 non-athletes, with brains screened for evidence of CTE in a blinded fashion.

Forty-two cases had CTE pathology (5.6 per cent of the total), while CTE was found in 27 athletes and 15 non-athletes; and in 41 men and one woman.

American football had the highest frequency of CTE (15 per cent) of the contact sports studied, with participation beyond high school resulting in the highest risk of developing CTE.

“Generally our findings point to CTE being more common in athletes and more common in football players, but this study is a bit more balanced and accurately reflects the general population compared to previous studies,” said lead author Kevin Bieniek, of UT Health San Antonio.

CTE, linked with repetitive blows to the head, has been found in 80-99 per cent of autopsied brains of pro American footballers.

Dr Bieniek said: “Nobody has really looked at it from kind of an epidemiological perspective. We compared people who played a sport with those who didn’t play. We studied both young and old people, and amateur players versus college and professional players. And we studied both men and women, which had not been done previously. What we aimed to do was an unbiased screen for CTE from all sorts of different cases.

“The 42 cases, or 6 per cent, is more of a grounded, realistic number. That might not seem like a lot, but when you consider there are millions of youth, high school and collegiate athletes in the United States alone who play organised sports, it has the potential of being a significant public health issue.

“There are many ongoing questions regarding CTE pathology, however, and we don’t want to discourage sources of healthy physical and cardiovascular activity like these sports. Rather, we emphasise safe strategies to reduce the possibility of head injuries and properly treat them when they are sustained.”

The identification of 15 CTE cases in non-athletes raises interesting questions, Dr Bieniek said.

“Did these people have trauma from another source? Were they actually athletes and we were unable to detect it from biographical information? Is there another disease with similar features?”

Cases with CTE tended to be slightly older than the cases without it, and many CTE cases also showed evidence of Alzheimer’s disease.