Summary: While being overweight may be bad for your general health, researchers discovered an association with higher body mass index (BMI) and a reduced risk of developing ALS. Those with a BMI considered to be in the obese range had a 31% reduced risk of developing ALS, while those considered overweight had an 18% lower risk.
People who have a high body mass index (BMI) or who gain weight as they get older may have a lower risk of amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, according to a large study published in the June 26, 2019, online issue of Neurology.
ALS is a rare, progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. People with ALS lose the ability to initiate and control muscle movement, which often leads to total paralysis and death. The average life span after diagnosis is two to five years.
BMI is a measure of a person’s body size based on their height and weight. People are considered underweight if they have a BMI lower than 18.5 kg/m2, healthy if it is between 18.5 and 24.9, overweight if they have a BMI of 25 to 29 and obese with a BMI 30 or higher.
“It is important to note that while our study found a link between high BMI and a lower risk of ALS, it is possible that genetics could make a person more likely to have both a low BMI and a higher risk of ALS without one causing another,” said study author Ola Nakken, MD, of the University of Oslo in Norway.
“People must not interpret the results of our study as a suggestion that gaining weight may prevent ALS. Plus, the health risks of having a high BMI would be greater than any protective effect.”
For the study, researchers reviewed a Norwegian database that included BMI measurements for the majority of people living in Norway between 1963 and 1975. Researchers included nearly 1.5 million people in the study, identifying 2,968 people who later developed ALS over an average of 33 years. Many people in the database also completed follow-up surveys about lifestyle and health, including weight change.
Researchers found that for every five-point increase in BMI from the low-normal BMI range, from the start to the end of the study, there was a 17-percent lower risk of developing ALS later. Of the 468,853 people in the low-normal range, 1,002 people developed ALS, or 0.21 percent. Of the 139,158 people in the obese range, 182 people developed ALS, or 0.13 percent.
After 50 years, participants had a 31-percent lower risk of developing ALS for every five-point increase in BMI.
The researchers also found that people who had a BMI in the obese range at the start of the study had a 34-percent lower chance of developing ALS compared to people in the low-normal BMI range, and people who had a BMI in the overweight range had an 18-percent lower risk.
Participants who gained the most weight had a 37-percent lower risk of ALS than those who didn’t gain weight or lost weight.
The results remained the same after adjusting for smoking, cholesterol levels and physical activity.
“While some cases of ALS are genetic, most cases do not appear to have a genetic cause, and an increasing body of evidence suggests that there may be a link between a fast metabolism that can lead to a low BMI and ALS,” said Nakken. “Much more research is needed to further examine the relationship between BMI and ALS.”
A limitation of the study was that most participants were white, so the results may not be the same for other populations.
About this neuroscience research article
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High BMI is associated with low ALS risk: A population-based study
Objective To investigate the temporal relationship among prediagnostic body mass index (BMI), weight change, and risk of amyotrophic lateral sclerosis (ALS).
Methods From the compulsory Norwegian tuberculosis screening program, we collected objectively measured BMI from 85% of all citizens (near 1.5 million) between 20 and 70 years of age living in 18 of 19 Norwegian counties between 1963 and 1975. For those who participated in later health surveys, we collected further information on weight change, lifestyle, and health. We identified ALS cases until September 2017 through national registries of diagnoses at death and at encounters with the specialist health service. Both Cox hazard models and flexible parametric survival models were fitted to address our research question.
Results We identified 2,968 ALS cases during a mean of 33 (maximum 54) years follow-up. High prediagnostic BMI was associated with low subsequent ALS risk across the typical ALS ages in both sexes. Overall, hazard ratio (HR) for ALS per 5-unit increase in prediagnostic BMI was 0.83 (95% confidence interval [CI] 0.79–0.88). After an initial increase during the first 10 years, it decreased almost linearly throughout the observation period and was 0.69 (95% CI 0.62–0.77) after 50 years. Those in the quartile with highest weight gain had lower ALS risk than those in the lowest quartile (HR 0.63, 95% CI 0.44–0.89). Conclusion High BMI and weight gain are associated with low ALS risk several decades later. The strength of the association between BMI and ALS risk increases up to 50 years after BMI measurement.