Tomatoes and Parkinson’s disease – an old hypothesis revisited

• We reflect on a hypothesis proposed in this journal in 1989, which speculated about tomatoes being a possible cause of PD • We summarize new evidence demonstrating an association between tomato cultivation and the fast worldwide growth of PD. • This observed association may reflect causality; pesticides used in tomato cultivation could affect the substantia nigra. • We emphasize the association may be spurious; it serves to illustrate the complexity of identifying the actual cause of PD. • We do underscore the need to better study the role of currently used pesticides – individually or in combination. In 1989, Jacob I. Sage proposed that tomatoes might contribute to the aetiology of Parkinson’s disease (PD). At the time, his hypothesis mainly served as a provocative “tongue-in-cheek” illustration of the complex challenges that come with identifying the true cause for a globally occurring disease that emerged as a largely new condition in the early 19th century. We here discuss why this hypothesis may have been less far-fetched than originally thought, using some circumstantial and observational evidence to underpin this idea. Specifically, growing evidence suggests that pesticide exposure is a relevant risk factor for PD and some seemingly neurotoxic pesticides are used to grow tomatoes. The number of pesticides used agriculturally, including on tomatoes, has increased in the past decades. Also, the prevalence of Parkinson’s disease seems to grow fastest in countries with the highest growth in tomato production. We fully acknowledge the speculative nature of our hypothesis, and that the provided circumstantial evidence by no means proves that tomatoes, and specifically pesticide application on tomato crops, are an actual cause of Parkinson’s disease. We do hope to raise further awareness for the notion that the global increase in the use of pesticides, compounded by a potential for cumulative neurotoxic effects due to exposure to mixtures of environmental chemicals, could exacerbate the global rise in PD, highlighting the need for improved risk assessments and preventative measures.