Does Traumatic Brain Injury Increase the Risk of Motor Neurone Disease? What New Research Reveals

Over the past decade, research has linked traumatic brain injury (TBI) and repetitive head impacts with neurodegenerative disease. Links with Dementia and Chronic Traumatic Encephalography (CTE) in particular ha dominated headlines, but links between head impacts and MND (also known as ALS) remains less clearly understood.

In October 2025, a major UK population study published in JAMA Network Open in October 2025 attempted to clarify this relationship using national electronic health records.

What the Research Found

Zhu et al. (2025) analysed health records from 342,760 adults, including over 85,000 individuals with documented traumatic brain injury.

Three findings stand out.

1) A higher observed risk of MND after TBI

Individuals with a history of TBI showed approximately a 2.6-fold higher risk of later receiving an MND diagnosis compared with matched members of the general population. In absolute terms, 69 of 85,690 people with TBI developed ALS (about 0.08%), while 81 of 257,070 matched controls developed ALS (about 0.03%).

At face value, this appears alarming, and it is easy to interpret this as evidence that brain injury causes MND, but the story is more nuanced.

2) No difference in disease timing or survival

The researchers found no difference in age at diagnosis or age at death between people with and without prior TBI.

If traumatic brain injury were directly accelerating disease progression, we might expect earlier onset or shorter survival. That was not observed.

3) The risk was confined to the first two years

The finding that deserves the most attention, is that increased risk existed only within two years after the injury. After that period, risk returned to baseline levels.

This led researchers to propose a concept many outside academia rarely hear discussed: reverse causality.

What is Reverse Causality?

MND often develops silently before diagnosis. Early symptoms can include subtle weakness, coordination changes, or balance issues long before disease is recognised.

Zhu et al. (2025) suggests that, in some individuals:

• early, undiagnosed MND may increase falls or accidents
• those events result in a recorded traumatic brain injury
• the neurological disease is diagnosed months or years later

In other words, the injury may not be causing the disease; the disease may be contributing to the injury. This distinction matters enormously for athletes, governing bodies, and public perception.

What This Means Sport

The current evidence does not prove that traumatic brain injury causes MND.

What it does show is an observable association, a strong possibility of reverse causality and significant gaps in long-term data.

The journeys of Rob Burrow and Doddie Weir increased awareness of MND in the public eye and Lewis Moody’s diagnosis reminds us that this is not a historical conversation, but an ongoing one. Rugby has already implemented meaningful change; increasing concussion awareness, introducing stricter protocols, appointing independent match-day doctors, enforcing graduated return-to-play pathways, and adapting laws to reduce head contact. Each represents a step forward.

Yet we are only at the beginning of understanding brain health across an athlete’s lifetime. The next breakthroughs may not come from looking harder at the brain in isolation, but from understanding the wider system around it, how forces move through the body and brain in different sports, how athletes adapt over time, and how subtle changes accumulate long before symptoms appear, and monitoring all known risk factors that influence brain health  both during and well beyond an athletes sporting career.