Legumes may lower risk of Parkinson’s symptoms with sleep disorder

Fewer prodromal symptoms in REM sleep behavior disorder patients in Korea

Lindsey Shapiro, PhD avatar

by Lindsey Shapiro, PhD |

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A diet rich in legumes — a food group including beans, soybeans, and lentils — was associated with a lower probability of Parkinson’s symptoms starting to appear, a stage called prodromal Parkinson’s disease, in adults under age 70 with REM sleep behavior disorder (RBD), a study in South Korea reports.

Prodromal Parkinson’s is an early disease stage — before its diagnosis — that’s typically marked by nonmotor Parkinson’s symptoms such as RBD, indicative of the neurodegenerative disease, rather than by its classic motor symptoms.

Overall diet quality among was the study’s roughly 100 RBD patients was similar to that of the general population in Korea and did not associate with a risk of prodromal Parkinson’s.

The study, “Diet quality and prodromal Parkinson’s disease probability in isolated REM sleep behavior disorder,” was published in Parkinsonism & Related Disorders.

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Expert Voices: Diet and Nutrition for People With Parkinson’s Disease

Diet tied to prodromal Parkinson’s and disease risk scores in Western countries

RBD, a sleep disorder characterized by physically acting out dreams during the REM phase of sleep, is one of prodromal Parkinson’s most strongly linked risk factors.

The International Parkinson and Movement Disorder Society (MDS) created a framework for calculating the likelihood of Parkinson’s being diagnosed in a person with prodromal symptoms, and for establishing a probability score based on a range of prodromal symptoms that cover RBD and other Parkinson’s risk factors.

Diet quality has been found to influence prodromal probability scores and Parkinson’s disease risk, the researchers noted, but such studies were largely conducted in Western countries and favored diets more common there, like the Mediterranean diet.

But “diets greatly vary between the East and West and … the relationship between diet and [prodromal Parkinson’s] probability has not yet been studied in Asian countries, including Korea,” the researchers wrote. “In addition, to our knowledge, no studies have reported the relationship between diet and [prodromal Parkinson’s] probability in patients with isolated RBD (iRBD), a group with a strong prodromal marker of [Parkinson’s disease] compared to the general population.”

Scientists examined whether diet quality influenced the likelihood of prodromal Parkinson’s in 101 REM sleep behavior disorder patients seen at a clinic in Seoul.

They assessed the overall probability of prodromal Parkinson’s using a web-based calculator set up by MDS, taking into account such prodromal symptoms as RBD, smell loss, constipation, excessive daytime sleepiness, orthostatic hypotension (a blood pressure drop upon standing), erectile dysfunction, urinary dysfunction, depression, cognitive decline, and motor or movement difficulties.

It also accounted for other Parkinson’s risk factors, such as pesticide exposure, caffeine use, and smoking.

Diet quality was determined using the Recommended Food Score (RFS), where higher scores — up to a maximum of 47 —indicate a better quality.

People with REM sleep behavior disorder known to be at risk for Parkinson’s

Enrolled patients had a mean age of 68.3 and a mean RFS score of 28.23, reflecting a diet quality similar to that observed in 1,714 age- and sex-matched people from the general population.

Patients were split into a low RFS and high RFS group, with a cutoff score of 30. Demographic variables were similar between the two groups, but a higher percentage of patients in the high RFS group did not use caffeine.

Across the entire group, the median likelihood of prodromal Parkinson’s was about 99%, which did not significantly differ between high and low RFS patients. Likewise, no individual prodromal markers differed between the groups.

The scientists noted that their data’s statistical power likely were limited due to all study participants having RBD, and thus a high probability of prodromal Parkinson’s.

Further analysis into food choices and four prodromal markers — smell loss, daytime sleepiness, depression, and constipation — were conducted to counter that bias.

Patients whose diet included higher amounts of four types of legumes — soybeans and their cooked form, miso soup/soybean paste, tofu, and soy milk — had one or no prodromal markers, while those who ate fewer such legumes had three or all four such markers, results showed.

Possibility that diet rich in legumes has ‘protective effects’ for Parkinson’s

“The negative correlation between legume consumption and both [prodromal Parkinson’s] probability and prodromal markers suggests legume consumption has protective effects,” the researchers wrote.

Moreover, in patients under age 70, a higher consumption of legumes was linked to a lower risk of prodromal Parkinson’s, and legume consumption was significantly higher in patients with fewer prodromal markers.

For patients older than age 70, the probability of prodromal Parkinson’s increased with an increasing RFS score, implying a better diet and “contrary to our expectations,” the researchers wrote.

“We suspect that this positive correlation may be due to the confounding effect of age,” they added, noting that this and other studies find RFS scores to rise with age in the Korean population.

Legumes, like soy plants, are known to contain a compound called isoflavone that has strong antioxidant activity, which could account for their benefits in Parkinson’s, according to the scientists.

Oxidative stress, a type of cellular damage marked by an imbalance between toxic reactive oxygen species and the antioxidant molecules that neutralize them, is implicated in the neurodegenerative disease.

Unlike Parkinson’s risk factors that can be changed, like caffeine consumption, smoking, and exercise, most prodromal markers are not considered modifiable.

A study into “whether legume consumption could modify these seemingly unmodifiable factors” would be worthwhile, the scientists wrote.

Likewise, “future studies are needed to determine whether legume consumption in patients actually delays conversion to [Parkinson’s disease],” they added.