BMC Public Health 2009, 9:1 http://www.biomedcentral.com/1471-2458/9/1 diagnosis of depression and 42 subjects without the diagnosis were included in the validation study. The percentage of confirmed depression was 74.2%; 95% CI: 63.3 – 85.1. The percentage of confirmed non-depres- sion was 81.1%; 95% CI: 69.1 – 92.9 (submitted article). Statistical analysis The analysis was stratified by sex. Non-conditional logistic regression models were fit to assess the relation- ship between body image disturbance and incidence of depression in our cohort. Odds Ratios (OR) and their 95% Confidence Intervals (CI) were calculated taking as the reference category those subjects who had agreement between the body size perception and self-reported BMI. Potential confounders included in the multivariate models were: age (continuous), working hours (< 35 hours/week, >= 35 hours/week, unemployed), weight gain in the past five years (none, lost, gain), marital status (unmarried, married, other), smoking (never, past smoker and current smoker), presence of any severe disease at baseline (cardiovascular and cancer), presence of any severe disease at follow-up (cardiovascular and cancer), alcohol intake (g/day, continuous), total energy intake (Kcal/day, con- tinuous) physical activity during leisure time (weekly MET-hours, continuous) and pregnancy at follow-up. All p values presented are 2-tailed; p < 0.05 was considered statistically significant. Results The mean follow-up of participants was 4.4 years (median = 4.2 years). Three hundred thirty eight participants initially free of depression reported a medical diagnosis of depression during this period (95 men and 243 women). In addition, there were 160 participants with no medical diagnosis of depres- sion, but who reported initiation of antidepressants (67 men and 93 women). Therefore, the overall cumulative incidence of depression in this population was 4.8% during the follow up period. We show in table 1 some characteristics of participants and non-participants of this study. The non-participants were older, consumed more energy, and worked less hours/week than participants. The non-participants also had a higher proportion of women, ex-smokers, over- weight, and obesity than participants. Table 2 shows the main characteristics of participants according to the categories of the variable 'body image disturbance'. Among men, those who overestimated their body size showed higher frequency of body weight gain in the past five years, and more of them were Table 1: Characteristics of participants and non-participants in the SUN study. Characteristics Incidence of depression (n, %) Age [years] (mean, SD)a Sex (n, %)a Male Female Body mass index [Kg/m2] (n, %)a Underweight Overweight Obese Weight change in the past five years [Kg] (n, %) Lost Gain Marital status (n, %)a Unmarried Married Other Body image (n, %) Underestimated Overestimated Participants (n = 10,286) 498 (4.8) 37.7 (11.9) 4368 (42.5) 5918 (57.5) 1469 (14.3) 2541 (24.7) 452 (4.4) 2466 (24.0) 4849 (47.1) 4597 (45.0) 5246 (51.4) 368 (3.6) 4542 (44.2) 265 (2.6) Non-participants (n = 8,771) 105 (1.2) 39.2 (12.6) 3115 (35.5) 5656 (64.5) 1370 (15.6) 2273 (25.9) 461 (5.3) 2128 (24.3) 4053 (46.2) 3727 (42.9) 4423 (50.9) 539 (6.2) 3474 (44.9) 230 (3.0) Standard deviation (SD), a Statistical significant difference. ex-smokers compared to those who underestimated or correctly perceived their body size. The men who overestimated their body size also were older and had lower average physical activity during leisure time than those who underestimated or correctly perceived their body size. Furthermore, among men who underesti- mated their body size there was a higher proportion of overweight and obesity than those who overestimated or correctly perceived their body size. Among women, those who overestimated their body size showed a higher proportion of underweight, and more of them were unmarried in comparison with those who underestimated or correctly perceived their body size. The women who overestimated their body size also had lower average age, lower alcohol consumption, and a greater proportion of unemployment than those who underestimated or correctly perceived their body size. We show in table 3 the results of the logistic regression models fitted to evaluate the association between body image disturbance and the incidence of depression. This relationship was not statistically significant in either sex. After additionally adjusting for the occurrence of pregnancy or the incidence of cardiovascular disease and cancer during follow-up, the association between body Page 4 of 9 (page number not for citation purposes)