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A single mild concussion while playing amateur sports does not lead to long-term cognitive decline a has found.

This conclusion may seem at odds with on head injury and concussion in sport. However, a closer look at the study shows its findings are not so different after all: experiencing repeated concussions is not a good thing.

The study is a part of a large-scale community based looking at how healthy brains age, and what factors may increase the risk of dementia. Given the recent high-profile brought with brain injuries and emerging evidence that concussion decreases cognitive function in , looking at past incidents of concussion in such a long-term study makes sense.

The study asked over 15,000 people between the age of 50-90 to remember their past incidents of head injury, including where or how they happened (for example, playing sport, in a car accident) – along with the symptoms experienced, such as loss of consciousness, dizzy spells and blurred vision. They also tested participants’ behaviour and cognitive abilities annually over four years.

The results showed that one mild concussion during sport did not cause any behavioural or cognitive problems later in life. In fact, those who’d suffered one mild concussion during sport performed a little better on some tests, possibly due to the overall benefits of regularly playing sport.

However, as the number of historic concussions increased, this effect disappeared, and performance did decline. Concussions outside of sport showed the same basic pattern – one concussion does not lead to poorer performance, but repeated concussions do.

Basically, no matter how you receive a concussion, the more you get, the greater your risk for a poorer long-term outcome. This is why professional sports people, , are at a higher risk of brain injury.

The study’s findings are complicated. It has a mix of results, split across different groups with different numbers of concussions.

The fact that having one concussion didn’t cause cognitive deficits doesn’t necessarily mean there is no injury. There is the concept of , the idea that the brain is resilient enough to take some damage, and still function normally.

This is a good thing. It’s a bit like how a tyre can still function with a little loss of air. If you reach a point where too much air has leaked out, and the tyre is flat, it doesn’t work anymore. In between, you may also notice a change in performance of the tyre.

It’s the same thing with any mild injury to the brain. A little bit and your brain may cope. But over time, if you add more injuries, performance declines, and you reach a point where your brain may be “flat”.

That’s why it’s essential to players from a game after a sports-related concussion.

Just having one concussion does not automatically mean you develop problems in later life. However, the more concussions or mild traumatic brain injuries you have, the worse the results are likely to be – whether you are a professional athlete or not.

This study only looked at – defined as a head injury followed by loss of consciousness of less than 30 minutes or feeling dazed or confused. More moderate or severe concussions are likely to have a greater effect, especially if these are numerous.

Conversely, one mild injury does not reduce all the benefits sport participation can bring for brain health. Factors related to sport participation such as and are known to have a positive effect on cognition later in life.

These, along with many other lifestyle factors – like not smoking, moderate alcohol consumption and eating a healthy diet – may all provide protection from life’s little bumps.