BMC Public Health 2009, 9:340 http://www.biomedcentral.com/1471-2458/9/340 more widely used HSCL-25, an instrument which mainly measures symptoms of anxiety and depression [36]. The questions in HSCL-10 concern the following symptoms during the last week: "Suddenly scared for no reason, feel- ing fearful, faintness or dizziness, feeling tense or keyed up, blaming yourself for things, trouble falling asleep, feeling blue, feeling of worthlessness, feeling everything is an effort, feeling hopeless about the future" [37]. Each item is rated on a scale from 1 (not at all) to 4 (extremely). An average score for all the 10 items is calculated and a score equal to or greater than 1.85 has been shown to be a valid predictor of mental health distress in subjects aged 16-24 years old [36]. For inclusion in the total HSCL-10 score, six of the ten questions had to be completed. The missing values were replaced by the sample mean for each value [36]. Diet This was self-reported and sugary soft drinks were dichot- omized into "seldom" (never, 1-6 glasses per week, 1 glass daily) versus "often" (2-3 glasses daily, more than 4 glasses daily). The other dietary variables (raw vegetables, fatty fish, chocolate/sweets and potato chips) were all dichotomized into "seldom" (never, 1-3 times a months, 1-3 times a week) versus "often" (4-6 times a week, 1-2 times a day, and 3 or more times a day). Lifestyle variables These are self-reported variables and cigarette smoking was trichotomized into "never", "has quit" or "some- times" and "daily". Alcohol was dichotomized into "sel- dom" (never, sometimes yearly and 1-3 times a month) versus "often" (once a week, 2-7 times a week). Socio-demographics The variable concerning both ethnicity and income was obtained from Statistics Norway which possesses infor- mation on all residents in Norway. Non-Western adoles- cents are defined as having both parents from a non- Western country or as having been born in a non-Western county [38]. Western Europe, North America and Aus- tralia are considered to be Western countries in the analy- ses. Other countries are considered to be non-Western [38]. Income is the total of both parents' gross income and has been divided into three categories: >1.0 million Nor- wegian kroner (NOK), NOK 1.0-0.5 million, and < NOK 0.5 million. One million NOK is approximately 105,000 Euros. Missing 3655 adolescents answered the question about acne, thus 120 missing (3.2%). On the other variables the missing numbers were as follows: mental distress 147, sugary soft drinks 161, raw vegetables 125, fatty fish 137, chocolate/ sweets 129 and potato chips 130, cigarette smoking 129, alcohol 174, ethnicity 415, income 708. Ethics The study protocol was evaluated by the Regional Com- mittee for Medical Research Ethics and approved by the Norwegian Data Inspectorate and the educational author- ities in Oslo. It has been conducted in full accordance with the World Medical Association's Declaration of Hel- sinki. Written, informed consent was obtained from all the participants. Statistics SPSS for Windows version 14.0 was used for the statistical analyses. Odds ratios (OR) were calculated in both crude and adjusted logistic regression models. The level of sig- nificance was set at p < 0.05 and 95% CI were calculated. Results The population characteristics in our study showed a slight preponderance of females (55.7%) and the majority of the adolescents come, as expected, from middle income families (53.1%) and have a Western background (76.4%). (Table 1). The prevalence of acne in the sample was 13.5% (95%CI; 10.5-16.5), reported non-significantly more often among the males than the females. The prevalence of acne among males with mental distress was 20.5% (95%CI; 15.3- 25.7%) which is significantly higher than among males without mental distress, 13.4% (95%CI; 11.6-15.2%). The prevalence of acne among females with mental dis- tress was 18.8% (95%CI: 15.9-21.1%) which is signifi- cantly higher than among females without mental distress, 9.6% (95%CI: 8.0-11.2%) (Table 2). These asso- ciations are also reflected in the estimated odds ratios in table 3. In an adjusted model including diet, lifestyle and socio-demographic factors, the adjusted association between acne and mental distress among the males showed an OR = 1.68 (95%CI:1.10-2.57) and among the females an OR = 2.04 (95%CI:1.50-2.77). When calculat- Table 1: Population characteristics of the sample of adolescents (N = 3775) Gender Income Ethnicity Boys Girls > 1.0 million NOK* 0.5-1.0 million NOK < 0.5 million NOK Non-Western Western N 1672 2103 729 1651 728 806 2611 % 44.3% 55.7% 23.5% 53.1% 23.4% 23.6% 76.4% * 1.0 million NOK is approximately 105,000 Euros Page 3 of 8 (page number not for citation purposes)