The Young Finns Study.

Acknowledging the lack of previous knowledge, we studied whether childhood/adolescent exposure to parental smoking associates with midlife cognitive function leveraging the data from the Cardiovascular Risk in Young Finns Study. A population-based cohort of 3,596 children/adolescents aged 3-18 years was followed-up between 1980-2011. Cognitive testing was performed in 2011 on 2,026 participants aged 34-49 years using a computerized test. Measures of childhood/adolescent second-hand smoke exposure were parental self-reports of smoking and participants' serum cotinine levels. Participants were classified into: 1)no exposure (non-smoking parents, cotinine<1.0ng/mL); 2)hygienic parental smoking (1-2 smoking parents, cotinine<1.0ng/mL); and 3)non-hygienic parental smoking (1-2 smoking parents, cotinine ≥1.0ng/mL). Analyses were adjusted for sex, age, family socio-economic status, polygenic risk score for cognitive function, adolescence/adulthood smoking, blood pressure and serum total cholesterol. Compared with non-exposed, participants exposed to non-hygienic parental smoking were at higher relative risk (RR) for poor (lowest quartile) midlife episodic memory and associative learning (RR=1.38, 95%CI=1.08-1.75) and a weak association was found for short term and spatial working memory (RR=1.25, 95%CI=0.98-1.58). The associations for those exposed to hygienic parental smoking were non-significant (episodic memory and associative learning: RR=1.19, 95%CI=0.92-1.54; short term and spatial working memory: RR=1.10, 95%CI=0.85-1.33). Avoiding childhood/adolescence second-hand smoking exposure promotes adulthood cognitive function.