Pesticides and Head Injuries – But Also Nuts, Red Meat and Soft Drinks – Linked to Parkinson’s Risk in Cyprus Study

Exposure to pesticides, severe head injury with fainting, and consumption of soda, nuts and red meat appear to be risk factors for Parkinson’s disease among people in Cyprus, a Mediterranean island with an interesting genetic mix, a study suggests.

Study results further suggest that smoking and eating fish are associated with a lower risk of Parkinson’s, and it confirms some previous findings of genetic associations with the disease.

“Genetic and Environmental Factors Contributing to Parkinson’s Disease: A Case-Control Study in the Cypriot Population” was published in Frontiers in Neurology.

It is well-established that both environmental and genetic factors contribute to an individual’s risk of Parkinson’s disease (PD), and many studies have looked for associations between these factors and the disease to determine what specific factors increase or decrease Parkinson’s risk.

Researchers here focused on people of Greek-Cypriot ethnicity living on Cyprus.

“[Cyprus] is a crossroad between Africa, Europe and Middle East. This made Cyprus a ‘genetic pool’ for transiting populations … characterized by genetic affinity with surrounding Southeast European and Near Eastern populations … [and] renders genetic studies in the Cypriot population informative for the genetically similar populations as well,” the researchers wrote.

They also investigated environmental factors for PD within Cypriot population, some of which “are of high prevalence,” and compared them with studies in populations elsewhere.

The researchers collected data — including medical histories, lifestyle factors, etc. — from 235 Cypriot people with Parkinson’s and 464 people without it as controls. There was a roughly even mix of males and females in both groups.

The Parkinson’s group was older than the control group (average age 70 vs. 64.5), had a significantly greater proportion of retired people (86% vs. 60.9%), and had a significantly lower body mass index (BMI).

Researchers created statistical models, which accounted for some of these inherent differences, to identify lifestyle and other factors relevant to a risk association.

They found that more frequently eating nuts and red meat, as well as consuming soft drinks more often, were associated with an increase in Parkinson’s risk of about two-fold (2.74 for nuts, 1.92 for meat, and 2.06 for soft drinks).

“PD cases had a significantly lower adherence to ‘healthy eating’ when compared to controls,” the researchers wrote.

They suggested the link with nuts might be due to pesticides accumulating in the nuts themselves or in the soil of trees they grow on.

“This is the first study detecting an increased risk for PD for moderate and heavy soft drinks consumers,” the researchers wrote. “A possible explanation could be given by a rat model study which demonstrated that carbonated soft drinks induced oxidative stress and also altered the expression of certain genes associated with brain activity.” But because soft drinks come in so many varieties, it’s “challenging to trace the component that could potentially cause neurodegeneration.”

Severe head injury with fainting was associated with a 2.42 times greater risk of Parkinson’s disease, and exposure to pesticides and other toxic substances with a 3.28-times higher risk.

Eating fish and smoking were both linked with about a three times lower chance of Parkinson’s (0.39- and 0.32-fold risk, respectively). Notably, coffee consumption was not analyzed as a predictor of Parkinson’s in this population, though the researchers noted that coffee consumption and smoking were closely linked with each other.

The researchers also looked at 13 gene mutations linked to Parkinson’s in previous studies. In this patient group, five of these variants were significantly associated with Parkinson’s in the same directions as previously reported. The variants rs12185268 in the SPPL2C  gene and rs17649553 in the MAPT gene — which provides instructions to make the tau protein — were linked with a lower Parkinson’s risk, while the variants rs13312 in USP24, rs6599389 in TMEM175, and rs356220 in SCNA — which provides instructions to make the alpha-synuclein protein — were associated with a greater risk.

“In conclusion,” the researchers wrote, “the current study has demonstrated a number of genetic and environmental predictors for PD [Parkinson’s disease] in the Cypriot population.”

“[E]xposure to both pesticides and other toxic substances, severe head injury accompanied with fainting, nuts consumption, red meat consumption, and soft drinks consumption were predisposing factors, whereas cumulative smoking and fish consumption were protective factors for PD risk. The association between [several gene mutations] and PD risk was replicated in the Cypriot population.”