Groeneveld et al. BMC Public Health 2011, 11:836 http://www.biomedcentral.com/1471-2458/11/836 at 6 and at 12 months. Of the intervention group, only those who had completed five or more counseling sessions on one of both topics (diet and PA, or smoking cessation) were included in the analyses. Of the control group, only those participants were included who had indicated not to have received counseling sessions and/or tailored lifestyle advice from any type of care provider, either face to face, by telephone, or computerized, between baseline and 6 months. Results Baseline characteristics and confounding In Figure 1 the participant flow is presented. 288 Partici- pants in the intervention group and 307 participants in the control group were included in the analyses. At base- line, in the EB group, 31.1% was a blue-collar worker and 69.9% was a white-collar worker, mean age was 47.4 years (standard deviation [SD] 8.8), mean BMI was 28.8 (SD 3.5), and 32.7% was a current smoker. BMI appeared to be a confounder for snack intake. For consistency reasons, all analyses in the EB group were adjusted for BMI. In the SC group, at baseline, 85.2% was a blue-collar worker and 14.8% was a white-collar worker, mean age and mean BMI were 46.8 (SD 8.9) and 27.8 (SD 3.2), respectively, and 100% was a current smoker. In the SC group, no con- founding by age or BMI was concluded, thus no adjust- ments were made. No adverse events of the intervention were reported by any of the participants. Physical activity In Table 1, the values for leisure time PA, sports, and MET-minutes at baseline, 6 and 12 months, and the results of the linear regression analyses are presented, for the EB group only. No statistically significant interven- tion effects were found for any of those variables at 6 or 12 months, although the improvements in leisure time PA, sports, and MET-minutes at six months were largest in the intervention group. BMI was an effect modifier for leisure time PA at 6 months. The normal weight partici- pants (BMI<25; n = 52) in the intervention group decreased the time spent on leisure time PA (b -133.3, 95%CI -330.7; 64.1), whereas the overweight (BMI≥25 and <30; n = 221) and obese (BMI≥30; n = 156) partici- pants increased their leisure time PA (b 68.9, 95%CI -29.6; 167.4 and b 104.6, 95%CI -15.7; 224.9). Age appeared to modify the 6- and 12-month effects of the intervention on leisure time PA as well. The intervention effect among participants aged 45 years and over (n = 254) was larger than among the younger ones (n = 175) at both 6 (b 88.8, 95%CI -10.1; 187.7 vs. b 21.0, 95%CI -76.6; 118.6) and 12 months (b 86.1, 95%CI -19.3; 191.5 vs. b -53.5, 95%CI -156.9; 49.9). In none of the BMI and age subgroups, statistically significant intervention effects were found. Page 4 of 9 Diet In Table 1, the values for fruit, vegetables, alcohol and snacks at baseline, 6, and 12 months, and the results of the linear regression analyses are presented, for the EB group only. At 6 months, a statistically significant beneficial intervention effect was found for snack and fruit intake, and a borderline significant effect was found for alcohol. At 12 months, the intervention effect on snack intake was still statistically significant. Due to effect modification by age, the intervention effect appeared statistically significant among participants aged 18-44 (b -3.2, 95%CI -5.9; -0.5) only, but not among those aged 45 and over (b -1.1, 95% CI -3.2; 1.1). At 12 months, the effect on alcohol intake was modified by BMI. The normal weight participants sig- nificantly lowered their alcohol intake as a result of the intervention (b -3.8, 95%CI -7.6; -0.04), whereas the over- weight and obese did not (b -0.8, 95%CI -2.9; 1.3 and b -0.4, 95%CI -2.7; 1.9). Smoking In Table 2, the results of the logistic regression analyses in the SC group can be found. At 6 months, 25 persons (31.3%) in the intervention group had quit smoking, as opposed to 11 (13.4%) in the control group. The odds ratio (OR) of smoking was 0.3 (95%CI 0.1; 0.7). Nine (36%) per- sons in the intervention group who quit smoking had used nicotine replacement therapy or medication, as opposed to 2 (18%) in the control group. The statistically significant effect was not sustained until 12 months follow-up (OR 0.8, 95%CI 0.4; 1.6). Age appeared a modifier of the inter- vention effect on smoking. The intervention was more effective among participants aged 45 years and over (n = 100) than for the younger ones (n = 62) at both 6 (OR 0.1, 95%CI 0.02; 0.5 vs. OR 0.7, 95%CI 0.2; 2.1) and 12 months (OR 0.4, 95%CI 0.1; 1.2 vs. OR 1.2, 95%CI 0.4; 3.8). Per protocol analyses According to the per protocol analyses, the differences between control and intervention group at both 6 and 12 months were larger than in the analyses of the study population as a whole. Again, the effect on fruit intake was statistically significant at 6 months (b 0.9, 95%CI 0.7; 3.1). Also, the effect on alcohol intake was statisti- cally significant at 6 months (b -1.7, 95%CI -3.2; -0.1). The effect on snack intake was statistically significant at 6 months (b -2.6, 95%CI -4.5; -0.6) and at 12 months (b -3.2, 95%CI -5.0; -1.5). The effect on smoking was statis- tically significant at 6 months (OR 0.1, 95%CI 0.05; 0.3) as well as at 12 months (OR 0.4, 95%CI 0.2; 0.99). Discussion Findings The aim of the study was to evaluate the effectiveness of a lifestyle intervention consisting of individual counseling