Among those showing signs of clinically meaningful anxiety, 42 percent of ex-footballers met the criteria while just 25 percent of people who never played did so.

Scans of the footballers brains showed clear reductions in grey-matter volume across regions tied to memory, focus, choices and mood control.

Overall brain size was also smaller and the players themselves judged their mental sharpness and decision skills as weaker than those of non-players.

"This represents the first large-scale look at mid-life brain health in retired footballers and the changes appear before typical clinical signs emerge," notes Heather Snyder, senior vice-president for medical and scientific relations at the Alzheimer's Association.

"The work suggests we may spot brain differences early enough to step in and support long-term health if we grasp the processes involved.

"Results such as these will guide players, doctors, leagues and families so they grasp possible risks tied to contact sports and can choose wisely."

The results add to mounting evidence that repeated head impacts in football may drive brain decline and related disorders.

Pinpointing exactly how and how much playing football, especially repeated heading, harms any one person's brain remains difficult because thorough examination is possible only after death.

Chronic traumatic encephalopathy, or CTE, stems from ongoing head strikes and appears more often in contact-sport athletes; confirmation requires post-mortem checks for protein buildup and tissue damage.

While alive, CTE may produce memory trouble, mood disorders, behaviour shifts and sudden anger.

"The UK has focused heavily on research into football's possible long-term effects on the brain," Snyder noted.

Former England forward Jeff Astle, who passed away in 2002 after prolonged neurological problems, is viewed as the first player whose death was tied to heading.

Several other former professionals and an amateur have since had their deaths officially connected to the sport.

Heading limits now apply in youth football across England, Scotland and Northern Ireland, and training rules differ in the professional leagues.

The 2019 Field study, backed by the FA and PFA, reported footballers faced 3.5 times the risk of neurodegenerative disease.

The FA responded with advice on cutting powerful headers during drills such as those from fast free-kicks and corners.

The Scottish FA went further by prohibiting heading the day before and after matches for adult professionals.

In 2023 the PFA and Premier League launched a brain-health fund to support former players and families dealing with dementia or similar conditions.

Researchers plan to track the same group of retired players over time and stress that further work is needed to uncover causes, track symptom progression and identify helpful steps.

"We must now determine why these brain shifts occur, what biology drives them and what the longer-term outcomes may be," Snyder said.

"Protecting the head from injury during sport remains one of the strongest ways to safeguard brain health."