Possible time-dependent sensitization to xenobiotics: self-reported illness from chemical odors, foods, and opiate drugs in an older adult population.

The present paper summarizes key features of time-dependent sensitization (TDS) in neuropharmacology (progressive amplification of behavioral, neuronal, endocrine, and/or immune responses to repeated intermittent exposures to an environmental agent or cross-sensitizing agents) as a possible model for cacosmia (subjective sense of feeling ill from low levels of environmental chemical odors) in nonindustrial and industrial populations; and extends previous cacosmia research in nonpatient populations to an elderly sample. This study examined the symptom and psychological profiles of 263 older adults (aged 60-90 y, 71% women, 29% men); 57% reported that at least one chemical and 17% reported that at least four of five chemicals (pesticide, automobile exhaust, paint, new carpet, perfume) made them feel ill. Cacosmia ratings correlated weakly and negatively with age (r = -0.19, p = .001) over the whole sample. Cacosmia correlated significantly with self-reported illness from foods that may mobilize or generate opioid peptides (wheat, dairy, eggs) (r = 0.32, p < .0001) and with illness from opiate drugs (r = 0.23, p < .0001). When the sample was divided into four cells on the basis of above-versus below-median total chemical-induced illness score (CI) and total food-induced illness score (FI), the high CI and high FI, high CI only, and high FI only groups had more frequent indigestion, and the high CI group had more frequent difficulty concentrating than the groups below median for illness from both chemicals and foods (NOILL), even after covarying for age and anxiety. The most cacosmic subjects noted higher prevalence of physician-diagnosed allergies and irritable bowel than did noncacosmic subjects. In contrast with previous young adult cohort studies, the older illness groups did not differ with regard to sex distribution, depression, shyness, or repressive defensiveness. When considered with prior surveys of young adults, the present findings are consistent with the presence of previously established, time-dependent sensitization to multiple xenobiotic agents in susceptible individuals for whom psychological variables do not explain the symptom of cacosmia. If cacosmia is a symptom of TDS, then the neuropharmacology literature suggests the possibility of excitatory amino acid, hypothalamic-pituitary-adrenal axis, dopaminergic, and/or opioid involvement. Prospective studies with objective measures testing the possible induction of TDS to specific chemicals are indicated.