The Young Finns Study (YFS) is a large follow-up study of cardiovascular risk factors from childhood to adulthood [29]. In total, 3596 children and adolescents aged 3–18 from all around Finland participated in the baseline study in 1980; they were followed up after, 3, 6, 9, 12, 21, 27, and 30 years, with comprehensive risk factor assessments, including smoking status and alcohol use. Cotinine and 3-hydroxycotinine were measured from all self-identified current smokers with available serum samples, and 714 subjects with cotinine above 10ng/ml and 1000Genomes imputed genome-wide genotype data available were included in the NMR GWAS analyses. For 166 subjects with repeated serum samples as current smoker, i.e. longitudinal metabolite data the NMR was assessed at the time of heaviest regular smoking (i.e. when cotinine was highest), although NMR can be used in light regular smokers [30].
