This blog post summarizes key findings from a study conducted by Claudia S. Miller and Howard C. Mitzel (1995) titled “Chemical Sensitivity Attributed to Pesticide Exposure Versus Remodeling.”
Author: Dr. Miller is professor emeritus at the University of Texas Health Science Center at San Antonio, Visiting Senior Scientist at the Harvard T. H. Chan School of Public Health, and Environmental Scientific Consultant to the Marilyn Brachman Hoffman Foundation. She has published extensively on chemical intolerance, having coined the term TILT to describe the disease process. Access her full study here.
The variety of symptoms reported by chemically sensitive individuals is vast. Similarly the types of exposures that produce such symptoms are variable from person to person. This variability of symptoms and exposures made it historically very difficult for doctors to identify an underlying common cause of illness for such patients. It was not until recent decades that early evidence of a common underlying disease mechanism began to surface. Such evidence was presented by Miller and Howard in 1995, and will be discussed in this blog. Originally called multiple chemical sensitivity (MCS), the common underlying disease mechanism explaining chemical intolerance has more recently come to be called toxicant-induced loss of tolerance, or TILT. Since the older term MCS was used throughout this study, however, we will stick with this older language in the study description the follows.
In this study, Miller and Howard recruited 112 individuals with self-reported onset of MCS following exposure to either (1) a cholinesterase-inhibiting organophosphate or carbamate pesticide or (2) remodeling of a building. Participants responded to a written questionnaire that covered their exposure event, medical history, and physical and cognitive symptoms that occurred after their exposures. They were asked to mark only symptoms that had developed or worsened following exposure. Importantly, there were no significant differences between the pesticide (PEST) and remodeling (RE) groups in terms of age, education, gender, and years lapsed since exposure.
The average age at onset of illness was 40 years. For PEST exposures, roughly 40% occurred in the work place, with about 55% at home, and only one case outdoors. Comparatively, more RE exposures occurred at work (~70%) than at home (~30%). For the PEST group, the pesticides most commonly implicated were chlorpyrifos, diazinon, malathion, and carbaryl. For the RE group, respondents were not asked about new carpet installation, yet about 60% nonetheless mentioned this as a supplementary comment.
In general, PEST and RE groups reported similar patterns of symptoms and identified similar inhalants and ingestants as triggers for their symptoms; thus, suggesting a common mechanism for their conditions. The PEST group reported worse symptoms than did the RE group, especially for neuromuscular, affective, airway, gastrointestinal, and cardiac symptoms. This was consistent with the underlying hypothesis of the study; namely, that if MCS resulted from neurotoxic exposures, then pesticide-exposed respondents should report greater severity of illness due to the relatively greater neurotoxicity of this class of chemicals.
Of respondents, 81% said they had been working full-time when initially exposed, yet at the time of the survey (on average, ~8 years post exposure) only about 15% were working full-time. The majority said they had quit their jobs, changed jobs or changed careers because of their illness. About 40% reported they had consulted 10 or more medical practitioners.
The results of this investigation were profound in that the persistent, disabling, neuropsychological symptoms reported by these MCS groups were similar to those reported among people occupationally exposed to pesticides and solvents. These parallel findings suggested that the types and levels of exposures associated with extermination and remodeling could be of substantial consequence to health, at least for a subset of the population. Further, the PEST and RE groups having reported similar patterns of symptoms and identified similar triggers suggested a common underlying mechanism for their conditions; thus, providing early evidence for the existence of TILT.