Literature Review

Does adherence to a Mediterranean diet reduce the risk of Parkinson’s disease?



Potential confounding

“This study pushes the prodromal criteria into performing a job they were never designed to do,” which presents potential pitfalls, Ronald B. Postuma, MD, of the department of neurology at Montreal General Hospital in Quebec, said in an accompanying editorial.

While the MDS criteria were designed to assess the likelihood that any person over age 50 years is in a state of prodromal Parkinson’s disease, the present study aimed to evaluate whether a single putative risk factor for Parkinson’s disease is associated with the likelihood of its prodromal state.

In addition, the analysis did not include some of the prodromal markers that are part of the MDS criteria, including olfaction, polysomnographic-proven REM sleep behavior disorder, and dopaminergic functional neuroimaging.

“As pointed out by the researchers, many of the risk factors in the prodromal criteria are potentially confounded by factors other than Parkinson’s disease; for example, one could imagine that older people, men, or farmers (with their higher pesticide exposure) are less likely to follow the Mediterranean diet simply because of different cultural lifestyle patterns,” Dr. Postuma said.

It is also possible that the Mediterranean diet affects prodromal markers such as constipation, sleep, or depression without affecting underlying neurodegenerative disease. In any case, the effect sizes observed in the study were small, and there was no evidence that participants who adhered most closely to a Mediterranean diet had less parkinsonism, Dr. Postuma said.

These limitations do not preclude physicians from recommending the diet for other reasons. “Numerous studies, reviews, meta-analyses, and randomized controlled trials consistently rank the Mediterranean diet as among the healthiest diets available,” Dr. Postuma said. “So, one can clearly recommend diets such as these, even if not necessarily for Parkinson’s disease prevention.”

Adding insights

The researchers used a Mediterranean diet score that was developed in a population of adults from metropolitan Athens, “an area not unlike the one in which the score is being applied in the HELIAD study,” Christy C. Tangney, PhD, professor of clinical nutrition and preventive medicine and associate dean for research at Rush University Medical Center, Chicago, said in a separate editorial. As expected, the average Mediterranean diet adherence score in this study was higher than that in the Chicago Health and Aging Project (33.2 vs. 28.2).

“If we can identify differences in diet or lifestyle patterns and risk of this latent phase of Parkinson’s disease neurodegeneration, we may be one step closer to identifying preventive measures,” she said. Follow-up reports from HELIAD and other cohorts may allow researchers to assess how changes in dietary patterns relate to changes in Parkinson’s disease markers, the probability of prodromal Parkinson’s disease, and incident Parkinson’s disease, Dr. Tangney said.

The study authors had no conflicts of interest or financial disclosures. The study was supported by a grant from the Alzheimer’s Association, an ESPA‐EU grant cofunded by the European Social Fund and Greek National resources, and a grant from the Ministry for Health and Social Solidarity (Greece). Dr. Maraki and a coauthor have received financial support from the Greek State Scholarships Foundation. Dr. Tangney and Dr. Postuma had no conflicts of interest.

SOURCE: Maraki MI et al. Mov Disord. 2018 Oct 10. doi: 10.1002/mds.27489.

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