Scans of retired British professional football players have shown structural differences in the brain and high rates of anxiety and depression, but no signs of cognitive decline, in a study aimed at determining whether repeated impacts such as heading the ball have an effect on the risk of developing dementia.

The study, conducted by researchers at Imperial College London, included 142 former players aged between 30 and 60, who were compared with 56 ordinary people in the same age group with no history of contact sports, military service, or previous concussions.

In addition to using questionnaires and tests to measure cognition, the researchers analyzed structural MRI brain images from a qualifying subset of 124 players and 40 people in the control group to check for differences in gray matter volume.

The study authors, who presented the findings at the Alzheimer's Association International Conference on Sunday, said the research is part of a major effort by scientists to address repeated head trauma as a potentially modifiable risk factor contributing to dementia in later life, similar to how doctors treat high blood pressure or cholesterol.

The study lays the groundwork for what is intended to be a longitudinal study of these players, whom the researchers plan to monitor every two years.

Lead study author Thomas Parker, a consultant neurologist at Imperial College London, said: "This field is taking a more holistic view of brain health and dementia risk."

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Memory and thinking tests

After adjusting for factors such as age and education, the former players performed as well as expected on memory and thinking tests, and showed no significant differences compared with the control group of healthy individuals.

The athletes reported significantly higher rates of mental health problems, with 31 percent reaching the threshold for clinical depression compared with 9 percent of the control group, and 42 percent of athletes reporting clinical anxiety compared with 25 percent.

The researchers found that brain scans of former players showed that this group had less brain tissue in areas that control memory and emotion compared with the control group.

However, only two percent of former athletes showed individual signs of severe brain shrinkage indicative of active and advanced neurodegeneration.

The study has not yet undergone peer review. The researchers expect to submit a paper with a larger sample and additional analyses later this year.