Occupational solvent exposure and cognition: does the association vary by level of education?
OBJECTIVE
Chronic occupational solvent exposure is associated with long-term cognitive deficits. Cognitive reserve may protect solvent-exposed workers from cognitive impairment. We tested whether the association between chronic solvent exposure and cognition varied by educational attainment, a proxy for cognitive reserve.


METHODS
Data were drawn from a prospective cohort of French national gas and electricity (GAZEL) employees (n = 4,134). Lifetime exposure to 4 solvent types (chlorinated solvents, petroleum solvents, benzene, and nonbenzene aromatic solvents) was assessed using a validated job-exposure matrix. Education was dichotomized at less than secondary school or below. Cognitive impairment was defined as scoring below the 25th percentile on the Digit Symbol Substitution Test at mean age 59 (SD 2.8; 88% of participants were retired at testing). Log-binomial regression was used to model risk ratios (RRs) for poor cognition as predicted by solvent exposure, stratified by education and adjusted for sociodemographic and behavioral factors.


RESULTS
Solvent exposure rates were higher among less-educated patients. Within this group, there was a dose-response relationship between lifetime exposure to each solvent type and RR for poor cognition (e.g., for high exposure to benzene, RR = 1.24, 95% confidence interval 1.09-1.41), with significant linear trends (p < 0.05) in 3 out of 4 solvent types. Recency of solvent exposure also predicted worse cognition among less-educated patients. Among those with secondary education or higher, there was no significant or near-significant relationship between any quantification of solvent exposure and cognition.


CONCLUSIONS
Solvent exposure is associated with poor cognition only among less-educated individuals. Higher cognitive reserve in the more-educated group may explain this finding.
Department of Society, Human Development, and Health, Harvard School of Public Health, Boston, MA, USA.
E L
EL
Sabbath
M M
MM
Glymour
C
C
Berr
A
A
Singh-Manoux
M
M
Zins
M
M
Goldberg
L F
LF
Berkman
D000368:Aged; D003071:Cognition / Q000187:drug effects*; D003072:Cognition Disorders / Q000139:chemically induced / Q000453:epidemiology / Q000209:etiology*; D058245:Cognitive Reserve / Q000187:drug effects; D015331:Cohort Studies; D004305:Dose-Response Relationship, Drug; D004522:Educational Status; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D009784:Occupational Diseases / Q000139:chemically induced* / Q000453:epidemiology; D016273:Occupational Exposure / Q000009:adverse effects*; D016017:Odds Ratio; D011446:Prospective Studies; D012179:Retirement; D012959:Socioeconomic Factors; D012997:Solvents / Q000009:adverse effects* / Q000737:chemistry
D012997:Solvents