Heavy exercise tied to earlier disease onset in ALS patients

People with amyotrophic lateral sclerosis (ALS) who have a history of strenuous exercise tend to develop the disease earlier than patients who were less physically active, according to a study.

However, data showed that heavy exercise does not increase the risk of death for ALS patients, and exercise itself does not increase the risk of developing the disease in the first place.

“Our study suggests a younger age of symptom onset in highly active individuals with ALS, adding weight to the evidence that strenuous exercise may contribute to an earlier disease onset in susceptible people,” researchers wrote.

The study, “Strenuous physical activity is associated with a younger age of amyotrophic lateral sclerosis onset in two independent cohorts,” was published in Brain Communications.

ALS is a neurological disorder in which the nerve cells that control movement gradually sicken and die. The causes of ALS are not fully understood; disease risk is thought to be influenced by factors ranging from genetics to environmental exposures to lifestyle habits.

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In search of a link

Some studies have suggested that people who engage in strenuous exercise are more likely to develop ALS. There’s also some data suggesting that exercise is linked to a younger age at onset and worse mortality outcomes in ALS. However, these links have not been proven.

Seeking to gain greater clarity, researchers at King’s College London analyzed data from two independent groups of ALS patients in the U.K. One consisted of data from 139 people with ALS who had died and donated their brains to the London Neurodegenerative Diseases Brain Bank. The other involved data on 166 ALS patients as well as 196 people without the disease from the Motor Neurone Disease (MND) Register of England, Wales and Northern Ireland.

Using standardized assessments, the researchers divided the patients into four groups based on the amount of strenuous exercise that they had engaged in throughout their lives. They then used statistical analyses to compare outcomes between patients in the top quartile (the most active patients) and those who had been less active.

In both groups, data consistently suggested that more strenuous exercise was associated with a significantly younger age at ALS onset. Among the post-mortem brain donors, the average age at onset was 54.2 for those who were highly active, compared with 63.9 for inactive patients. In the MND register, highly active patients developed the condition at a median age of 58, while median age at onset was 63 for inactive people.

Together, the findings suggested that patients with a history of strenuous exercise tended to develop the disease in their mid-50s, whereas inactive patients usually developed symptoms in their early 60s. Statistical analyses also showed that the risk of earlier disease onset was two to three times higher in highly active people.

The statistical models, however, showed no significant association between exercise and survival among ALS patients, nor was exercise linked with an increased risk of developing ALS. In contrast, the researchers noted that people with a history of head injury — a well-established disease risk factor — were 72% more likely to develop ALS.

“These findings further highlight the complex relationship between physical activity, head injury (including repetitive mild head injury from contact sports) and disease risk,” the researchers wrote. “We propose that strenuous exercise alone may be associated with early-onset ALS, possibly in predisposed individuals, whereas head injury may be related to risk of ALS development or associated through reverse causation.”

The scientists emphasized a need for more research into exactly how exercise and other risk factors interconnect to affect ALS disease processes.