Study from Norway links physical activity to lower ALS risk in men

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Men who are more active and physically fit have lower long-term risk of developing amyotrophic lateral sclerosis (ALS), according to findings from a large Norwegian study.

No such link was observed in female patients, for reasons that are not entirely clear.

The results may counter a concern that higher physical activity may lead to ALS, given the high number of professional athletes that have been diagnosed with the neurodegenerative disease.

“Our findings show that, for men, not only do moderate to high levels of physical activity and fitness not increase the risk of ALS, but that it may be protective against the disease,” first author Anders Myhre Vaage, MD, of Akershus University Hospital in Norway, said in a press release. “Future studies of the connection between ALS and exercise are needed to consider sex differences and higher or professional athlete physical activity levels.”

The study, “Physical Activity, Fitness, and Long-Term Risk of Amyotrophic Lateral Sclerosis,” was published in Neurology.

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Higher disease rates among athletes

In ALS, the nerve cells involved in voluntary muscle control, known as motor neurons, progressively degenerate. As a result, patients experience muscle weakness that gradually evolves toward paralysis, as well as problems with breathing, speaking, and swallowing.

The exact cause of ALS is not known, but it is believed to arise from a combination of genetic and environmental factors.

ALS is also referred to as Lou Gehrig’s disease, after the American baseball player who died from the condition in 1941 at the age of 37. Since then, a number of professional athletes have also been diagnosed with the rare disease at relatively young ages.

Studies have consistently found higher rates of ALS among professional soccer players, American football players, top performing cross-country skiers, and triathletes.

“The diagnosis of prominent athletes with ALS at young ages has sparked the uncomfortable idea that higher physical activity could be tied to developing ALS,” Myhre Vaage said.

The relationship between ALS risk and moderate physical activity and fitness levels in the general population has not been established, and results have been conflicting.

The researchers examined data from 373,696 people who participated in a large Norwegian cardiovascular health survey from 1985-1999, most of whom were in their 40s at study enrollment.

Participants self-reported their physical activity levels, which were ultimately grouped into three categories for the analysis: low (sedentary), medium (at least four weekly hours of walking or cycling), or high, with at least four weekly hours of recreational sports or heavy gardening or participation in hard training or sports several times per week.

They also underwent a physical exam to look at factors including height, weight, and resting heart rate. Other national health databases were  used to follow participants for a mean of about 27 years to look for the development of ALS.

Over the course of follow-up, 504 people developed ALS, 59% of them men.

Across the entire study population, participants with the highest activity levels were found to be at a nearly 30% lower risk of ALS compared with sedentary people, even when accounting for factors such as sex, age, smoking, and body mass index.

However, when looking at women and men separately, this association was only observed in men. In their case, both high and intermediate physical activity levels were associated with a reduced ALS risk relative to low activity levels — by 41% and 29%, respectively.

Moreover, a lower resting heart rate — an indicator of better physical fitness — was associated with a 32% lower risk of ALS relative to higher heart rate in male participants.

In female participants, no relationships between physical activity or resting heart rate and ALS were identified. The underlying mechanisms of the sex differences observed in the study are “not clear,” according to the researchers.

“In conclusion, moderate to high levels of physical activity and fitness in middle age do not increase ALS risk,” the researchers wrote. “Rather, it may be protective against the disease, but only in men.”

A limitation of the study was that physical activity questionnaires were only completed once at study enrollment, and thus may not have captured changes in exercise levels over the almost three decades of observation.

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