Cross-sectional and prospective associations of meeting 24-h movement guidelines with overweight and obesity in preschool children.

BACKGROUND: Cross-sectional studies report that meeting the newly developed 24-h movement guidelines (≥60 min moderate to vigorous physical activity (MVPA), ≤120 min screen time and 9-11 h sleep duration) are associated with lower adiposity indicators in children. However, prospective data are absent. METHODS: The study sample consisted of 830 children from the PRIMROSE study with GT3X+ accelerometer measured physical activity and parent reported screen time and sleep duration at age 4 years and objectively measured anthropometrics at age 4 and 5 years. The main outcome variables were weight status, body mass index (BMI) and BMI z-score at ages 4 and 5 years. Exposure variables were defined as meeting vs. not meeting the 24-h movement guidelines and combinations of these recommendations. RESULTS: On average, 18.4% of the total study sample met the combination of MVPA, sleep duration and screen time recommendations. In isolation, the MVPA, screen time and sleep guidelines were met by 31%, 63% and 98% of the total study sample, respectively. Adherence to any single recommendation, or any combination of recommendations at age 4 years, was not associated with being overweight or obese nor with BMI and BMI z-score at age 4 or 5 years. CONCLUSIONS: In contrast to previous cross-sectional studies, neither individual movement behaviours nor combinations of behaviours at age 4 years was associated with overweight or obesity, BMI or BMI z-score at age 4 or 5 years. More prospective data are needed before effects on weight status from meeting the 24-h movement guidelines are elucidated.

Body size and risk of atrial fibrillation: a cohort study of 1.1 million young men.

BACKGROUND: Whilst tall stature has been related to lower risk of vascular disease, it has been proposed as a risk factor for atrial fibrillation. Little is known about other anthropometric measures and their joint effects on risk of atrial fibrillation. OBJECTIVES: We aim to investigate associations and potential joint effects of height, weight, body surface area (BSA) and body mass index (BMI) with risk of atrial fibrillation. METHODS: In a cohort covering 1 153 151 18-year-old men participating in the Swedish military conscription (1972-1995), Cox regression was used to investigate associations of height, weight, BSA and BMI with risk of atrial fibrillation. RESULTS: During a median of 26.3 years of follow-up, higher height was associated with higher risk of atrial fibrillation (hazard ratio [HR] 2.80; 95% CI 2.63-2.98; for 5th vs. 1st quintile) and so was larger BSA (HR 3.05; 95% CI 2.82-3.28; for 5th vs. 1st quintile). Higher weight and BMI were to a lesser extent associated with risk of atrial fibrillation (BMI: 1.42; 95% CI 1.33-1.52, for 5th vs. 1st quintile). We found a multiplicative joint effect of height and weight. Adjusting for muscle strength, exercise capacity and diseases related to atrial fibrillation attenuated these measures. CONCLUSIONS: Higher height and weight are strongly associated with higher risk of atrial fibrillation. These associations are multiplicative and independent of each other and are summarized in a strong association of body surface area with risk of atrial fibrillation. The mechanisms remain unknown but may involve increased atrial volume load with larger body size.

Mental distress in treatment seeking young adults (18-25 years) with severe obesity compared with population controls of different body mass index levels: cohort study.

Young adults (18-25) with severe obesity constitute a challenging patient group, and there is limited evidence about their mental health status compared to population controls. Mental distress in treatment seeking young adults with severe obesity (n = 121, mean body mass index [BMI] = 39.8 kg m-2 ) was compared with matched (1:3 for age, gender and socioeconomic status) population controls of normal weight (n = 363, mean BMI = 22.4 kg m-2 ), as well as unmatched population controls with class I obesity (n = 105, mean BMI = 32.1 kg m-2 ) or severe obesity (n = 41, mean BMI = 39.7 kg m-2 ). Mental distress was measured by the General Health Questionnaire-12 (GHQ-12), and we quantified physician-diagnosed depression, present anxiety and suicide attempts. Poisson regression and linear regression analysis were used for analysing differences in mental distress between groups. Treatment seekers experienced more mental distress than normal weight controls as measured by continuous (adjusted mean: 3.9 vs. 2.2 points, P <0.001) and categorical (cut-off for mental distress ≥3 points, RR: 1.76, P <0.001) GHQ-12 scores, depression (RR: 2.18, P < 0.001), anxiety (RR: 1.97, P < 0.001) and suicide attempts (RR: 2.04; P = 0.034). Treatment seekers also experienced more mental distress as measured by continuous GHQ-12 than controls with class I obesity (adjusted mean: 2.3 points) or severe obesity (adjusted mean: 2.1; both, P < 0.001). Young adult treatment seekers with severe obesity constitute a risk group for mental distress compared to population controls of different BMI levels.

U-shaped association of body mass index in early adulthood with unintentional mortality from injuries: a cohort study of Swedish men with 35 years of follow-up.

OBJECTIVES: To investigate the dose-response association between body mass index (BMI) in young adulthood and the risk of mortality caused by unintentional injuries. METHODS: We performed a cohort study including 7 43 398 men identified by linkage of the Multigeneration Register and the Military Service Conscription Register. Cox regression models were used to examine crude and adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) of the relationships between BMI at age 18-20 years and the risk of death from all unintentional injuries as well as from specific unintentional injuries. We then estimated the population attributable fractions (PAFs)-the proportion of unintentional deaths that was attributable to underweight, overweight and obesity in this population-based cohort. RESULTS: During 35.9 years of follow-up, 6461 deaths occurred from unintentional injuries, including 3064 deaths from road injury, 978 from poisoning, 503 from falls, 243 from fire and 348 from drowning. Underweight subjects had a higher risk of mortality in all unintentional injuries (HR, 1.05; 95% CI, 1.03-1.10) and mortality in burns (HR, 1.65; 95% CI, 1.13-2.40) compared with BMI between 18.5 and 22.5 kg m(-2) (reference group). BMI >25 kg m(-2) was associated with increased risk of death from all unintentional injuries (HR, 1.36; 95% CI, 1.12-1.65) and road accidents (HR, 1.50; 95% CI, 1.14-1.97). Estimates of PAF suggested that 4.4% of the mortality in Swedish men caused by unintentional injuries could have been avoided if BMI values were kept between 18.5 and 22.5 kg m(-2). CONCLUSIONS: A U-shaped association was observed between BMI and risk of unintentional death. Both underweight and overweight were associated with increased mortality risk for all unintentional injuries and for subtype causes. Our study suggests that BMI might be a significant target for preventive interventions on deaths caused by unintentional injuries.

Changes in eating behaviour and food choices in families where the mother undergoes gastric bypass surgery for obesity.

BACKGROUND/OBJECTIVES: There is a lack of research exploring the effects of Roux-en-Y gastric bypass (RYGB) surgery on the patient's family's eating behaviour and food choices. The aim of the current study was to investigate changes in partners' and children's eating behaviour and food choices following maternal RYGB. SUBJECTS/METHODS: Sixty-nine women and their families were recruited from RYGB waiting lists at five Swedish surgical clinics. Data were collected during home visits 3 months before and 9 months after RYGB. Anthropometrical measures were taken, the adults completed the Three-Factor Eating Questionnaire and the children completed the Children's Eating Attitudes Test (ChEAT). All participants also completed a short food frequency questionnaire. RESULTS: Changes in scores were analysed using paired t-tests for unadjusted estimates or linear regression models with robust variance (General Estimating Equations) in order to enable age- and sex-adjusted estimates for the children. There were no meaningful differences in the partners' eating behaviour or food choices. The boys, but not the girls, improved their ChEAT scores, as did the overweight/obese children in comparison with the normal-weight children. The boys, unlike the girls, also decreased their intake of soft drinks, as did the normal-weight children when compared with the overweight/obese children. CONCLUSIONS: No clear-cut changes were found in partners' eating behaviour and food choices. Eating attitudes and soft drinks intake were improved among boys but not among girls. Differing modelling behaviour may partially explain these findings, but available data did not allow us to understand the underlying mechanisms.

Differences in gestational weight gain between pregnancies before and after maternal bariatric surgery correlate with differences in birth weight but not with scores on the body mass index in early childhood.

BACKGROUND: Large maternal gestational weight gain (GWG) is associated with increased birth weight and increased risk of obesity in offspring, but these associations may be confounded by genetic and environmental factors. The aim was to investigate the effects of differences in GWG in all three trimesters on differences in birth weight and in body mass index (BMI) scores at 4 and 6 years of age, within siblings born before and after bariatric surgery. METHOD: Women with at least one child born before and one after bariatric surgery were identified in national Swedish registers. Series of weight (and height) measurements were collected from antenatal medical records, with data on the nearest pregnancies before and after bariatric surgery. RESULTS: The age-adjusted means of pre- and post-operative GWG of 124 women were 11.3 (standard deviation [SD] 7.2) and 8.3 (SD 6.4) kg, respectively (P = 0.01). Adjusted fixed effects regression models showed positive associations of differences in mean total GWG with differences in siblings' birth weight, 0.023 kg per 1-kg greater weight gain (95% confidence interval [CI]: 0.014-0.069) and for second trimester 0.53 kg for each 1-kg greater weight per week (95% CI: 0.32-1.61), whereas no associations were found with BMI in pre-school age. CONCLUSION: This study showed positive associations between differences in total and second trimester maternal GWG and differences in children's birth weight, but no association with BMI scores in pre-school age. Maternal genetic, social and lifestyle factors fixed from one pregnancy to the next were taken into account in the analyses by the study design.

Modifiable environmental influences on body mass index shared by young adult brothers.

OBJECTIVES: Twin and adoption studies suggest that family environment has little, if any, influence on body mass index (BMI) in adulthood. We investigated the hypothesis that the differences in the years of birth between siblings influence their similarity in BMI at comparable ages, which would give evidence for a possibly modifiable influence of the environment shared by family members. METHODS: Swedish full-brother pairs (N=261 712) born between 1951 and 1983 were measured for BMI in conscription examination at 16-26 years (median: 18.2 years) of age and were divided into quartiles by the difference between their birth-years (< 2.25 years, 2.25-3.33 years, 3.34-5.08 years and >5.08 years). Furthermore, 1961 dizygotic twin brother pairs from the same population representing brothers born at the same time were included. In addition, the log BMI of the younger brother was modeled as a linear function of the log BMI of the older brother. Subsequently, the significance of the interaction between birth-year difference and the BMI of the older brother was tested. RESULTS: Intraclass correlation for BMI in dizygotic twin pairs was higher (0.431, 95% confidence interval (CI) 0.394-0.466) than the correlation for full-brothers in the first quartile of birth-year difference (0.376, CI 0.342-0.408). Among full-brothers, the BMI correlation decreased from 0.376 (CI 0.342-0.408) [corrected] in the first quartile to 0.338 (CI 0.331-0.345) in the last quartile. The regression analysis showed a statistically significant decrease in correlation with increasing birth-year difference (P<0.001). CONCLUSION: The influence on BMI in young men of the environment shared by dizygotic twin brothers is greater than between non-twin full-brothers, indicating important influences of concomitant exposure to the same early life environment before and/or after birth. Among non-twin siblings there is a slight possibly modifiable influence as evidenced by declining correlations by increasing distance in years of birth.

Impact of mental health problems on case fatality in male cancer patients.

BACKGROUND: Although mortality rates are elevated in psychiatric patients relative to their healthy counterparts, little is known about the impact of mental health on survival in people with cancer. METHODS AND RESULTS: Among 16 498 Swedish men with cancer, survival was worse in those with a history of psychiatric hospital admissions: multiply-adjusted hazard ratio (95% confidence interval) comparing cancer mortality in men with and without psychiatric admissions: 1.59 (1.39, 1.83). CONCLUSION: Survival in cancer patients is worse among those with a history of psychiatric disease. The mechanisms underlying this association should be further explored.

Bariatric surgery reduces mortality in Swedish men.

BACKGROUND: Mortality is lower in obese patients who have undergone surgery for obesity than in those who have not. The majority of patients in these studies have been women. Perioperative mortality is known to be higher among men, and this may counterbalance the survival advantage seen after surgery. This cohort study compared mortality among operated obese patients, non-operated obese patients and a general control cohort of men. METHODS: The study was based on record linkage between Swedish registries. An operated obese, a non-operated obese and a general control cohort were created. The two non-operated cohorts were assigned pseudosurgery dates. Data regarding preoperative and postoperative morbidity were collected, as well as mortality data. RESULTS: Hazard ratios were calculated for mortality between the cohorts adjusting for preoperative morbidity and age. Comparison of all-cause mortality for the obese surgical and non-surgical cohorts gave an adjusted mortality risk of 0.7 (95 per cent confidence interval (c.i.) 0.5 to 1.0) (P = 0.039); the adjusted mortality risk was 1.5 (95 per cent c.i. 1.1 to 2.0) (P = 0.011) when the obese surgical cohort was compared with the general control cohort. CONCLUSION: Bariatric surgery reduces overall mortality in obese men.

Intelligence in early adulthood and subsequent risk of unintentional injury over two decades: cohort study of 1 109 475 Swedish men.

BACKGROUND: There is growing evidence of an inverse association between intelligence (IQ) and unintentional injuries. METHODS: Analyses are based on a cohort of 1 109 475 Swedish men with IQ measured in early adulthood. Men were followed up for an average 24 years, and hospital admissions for unintentional injury were recorded. RESULTS: 198 133 (17.9%) men had at least one hospital admission for any unintentional injury during follow-up. The most common cause of unintentional injury was falling, followed by road accidents, poisoning, fire and drowning. In addition, 14 637 (1.3%) men had at least one admission for complications of medical care. After adjusting for confounding variables, lower IQ scores were associated with an elevated risk of any unintentional injury (HR (95% CI) per SD decrease in IQ: 1.15 (1.14 to 1.15)) and of cause-specific injuries other than drowning (poisoning (1.53 (1.49 to 1.57)), fire (1.36 (1.31 to 1.41)), road traffic accidents (1.25 (1.23 to 1.26)), medical complications (1.20 (1.18 to 1.22)) and falling (1.17 (1.16 to 1.18))). These gradients were stepwise across the full IQ range. CONCLUSIONS: Low IQ scores in early adulthood were associated with a subsequently increased risk of unintentional injury. A greater understanding of mechanisms underlying these associations may provide opportunities and strategies for prevention.

Paternal and maternal ages at conception and risk of bipolar affective disorder in their offspring.

BACKGROUND: A consistent association between paternal age and their offspring's risk of schizophrenia has been observed, with no independent association with maternal age. The relationship of paternal and maternal ages with risk of bipolar affective disorders (BPAD) in the offspring is less clear. The present study aimed at testing the hypothesis that paternal age is associated with their offspring's risk of BPAD, whereas maternal age is not. METHOD: This population-based cohort study was conducted with individuals born in Sweden during 1973-1980 and still resident there at age 16 years. Outcome was first hospital admission with a diagnosis of BPAD. Hazard ratios (HRs) were calculated using Cox's proportional hazard regression. RESULTS: After adjustment for all potential confounding variables except maternal age, the HR for risk of BPAD for each 10-year increase in paternal age was 1.28 [95% confidence interval (CI) 1.11-1.48], but this fell to 1.20 (95% CI 0.97-1.48) after adjusting for maternal age. A similar result was found for maternal age and risk of BPAD [HR 1.30 (95% CI 1.08-1.56) before adjustment for paternal age, HR 1.12 (95% CI 0.86-1.45) after adjustment]. The HR associated with having either parent aged 30 years or over was 1.26 (95% CI 1.01-1.57) and it was 1.45 (95% CI 1.16-1.81) if both parents were >30 years. CONCLUSIONS: Unlike schizophrenia, the risk of BPAD seems to be associated with both paternal and maternal ages.

Association between offspring intelligence and parental mortality: a population-based cohort study of one million Swedish men and their parents.

BACKGROUND: An inverse association of IQ with mortality has been observed in previous studies. Analyses of associations between offspring's IQ and parental mortality in biological and non-biological family relations may shed light on genetic and environmental influences. METHODS: In a target cohort of 1,235,375 Swedish men, 931,825 (75%) men had complete data on all variables used. IQ of offspring was measured at age 18 and mothers and father were followed, on average, for 21.2 years and 19.7 years, respectively, with respect to all-cause and cause-specific mortality (cardiovascular disease, coronary heart disease, stroke and diabetes). The analyses were conducted by proportional hazards regression with adjustment for parental occupation, education and income. RESULTS: In adjusted analyses using IQ as a continuous variable over a standard nine-point scale, hazards ratio (HR) for all-cause mortality was 0.96 (95% CI 0.96 to 0.96) for fathers and 0.95 (0.95 to 0.95) for mothers. The corresponding HRs were 0.99 (0.97 to 1.00) for step-fathers and 0.97 (0.95 to 0.99) for step-mothers. In adjusted analyses, HRs for CVD mortality among fathers and mothers were 0.97 (0.96 to 0.97) and 0.94 (0.93 to 0.94) respectively. The corresponding HRs for diabetes mortality were 0.91 (0.89 to 0.92) among fathers and 0.85 (0.83 to 0.87) among mothers. CONCLUSIONS: The associations found in non-biological family relationships suggest shared environmental influences and/or assortative mating. Stronger IQ-mortality associations in biological than non-biological relationships suggest genetic influences. Stronger inverse offspring IQ-parental mortality associations in mothers than in fathers might be due to environmental factors or epigenetic mechanisms.

Height and body mass index in young adulthood and risk of schizophrenia: a longitudinal study of 1 347 520 Swedish men.

OBJECTIVE: Measures of body size reflect genetic and environmental influences on growth and energy balance. Associations between such measures and risk of schizophrenia have been inconsistent. METHOD: This is a population-based cohort study of 1 347 520 men born in Sweden from 1952 to 1982, with height and body mass index (BMI) data available from conscription records. The Swedish National Hospital Discharge Register was used to identify subjects diagnosed with schizophrenia from 1970 to 2000. RESULTS: Subjects with lower BMI and shorter height had an increased risk of developing schizophrenia. Underweight subjects had an approximately 30% increase in risk compared with normal BMI subjects (adjusted HR = 1.30, 95% CI: 1.20-1.42). Tall subjects had an approximately 15% reduction in risk compared with short subjects (adjusted HR = 0.85, 95% CI: 0.80-0.92). CONCLUSION: Both height and BMI in early adulthood are strongly and inversely associated with risk of schizophrenia. We discuss these findings in relation to possible genetic and nutritional causal mechanisms.

Sugar-sweetened and artificially sweetened soft drinks in association to restrained, external and emotional eating.

We studied sugar-sweetened soft drinks and light soft drinks in their associations to psychological constructs of eating behavior and demographic data for adults and children. Soft drink intakes were assessed by consumption of soft drinks in number of days the last week, and eating behavior was measured by the Dutch Eating Behaviour Questionnaire (DEBQ). The sample included 3265 men and women, and their 12-year old children, originating from Swedish national databases. Associations to younger age and lower education in adults were in particular apparent for sugar-sweetened soft drinks. Consumption of sugar-sweetened soft drinks was further associated to less restrained and more external eating in adults. In contrast, light soft drinks were associated with higher BMI, more restrained eating and also more emotional eating in adults. For the children these associations were generally weaker. Sugar-sweetened soft drinks are consumed by persons with a lower education, who furthermore are less prone to attempt to restrict their calorie intake, and by some of those who are sensitive to external stimuli of foods. Light soft drinks are rather chosen by the more heavy persons who try to restrict their energy intake perhaps in order to control the body weight, and more unexpectedly, by adults who eat for comfort. Being more sensitive to an external stimulus of food such as taste seems to imply proneness to consume sugar-sweetened soft drinks instead of the light versions. Light soft drinks may be perceived as an adequate substitute in the use of foods for comfort, meaning the sweet taste may be sufficient for this purpose.

Genetic and environmental factors in relative weight from birth to age 18: the Swedish young male twins study.

OBJECTIVES: To investigate the contributions of genetic and environmental factors to the development of relative weight during the growth period. DESIGN: Longitudinal twin study. SUBJECTS: Two-hundred and thirty-one monozygotic and 144 dizygotic complete male twin pairs born between 1973 and 1979 were measured annually from birth to 18 years of age. RESULTS: Body mass index (BMI, kg/m(2)) at age 18 correlated with BMI at age 1 (r=0.32, 95% confidence intervals (CI) 0.21-0.42), and this correlation increased steadily up to age 17 (r=0.91, 95% CI 0.89-0.93). Major part (81-95%) of these trait correlations was attributable to correlate additive genetic factors, but also unique environmental correlations were present during the whole-growth period. The correlation between ponderal index (kg/m(3)) at birth and BMI at age 18 was small (r=0.09, 95% CI 0.02-0.15) and totally because of correlated unique environmental factors. CONCLUSIONS: Our results suggest persistent genetic regulation of BMI from age 1 to 18. However, environmental factors, not shared by siblings, also affected the correlations of BMI. A small specific environmental correlation was found between ponderal index at birth and BMI at age 18, which may reflect the effect of neonatal environmental factors on adult BMI. A challenge to the future research is to identify chromosome regions and specific genes regulating the development of BMI as well as environmental factors affecting BMI through the growth period independently or interacting with genetic factors.

IQ in early adulthood and later cancer risk: cohort study of one million Swedish men.

BACKGROUND: While several studies have reported an inverse relation between IQ and total mortality rates, little is known about the association, if any, between IQ and disease-specific outcomes, particularly cancer. METHODS: A cohort of 959,540 Swedish men who underwent IQ testing at military conscription at around 19 years of age, and who were followed for incident cancer. Hazards ratios for the relation between IQ and 20 cancer outcomes were computed using Cox regression. RESULTS: During an average of 19.5 years of follow-up, there were 10 273 new cancer cases. IQ showed few associations with the cancer end points studied. There was a suggestion that IQ was positively associated with lung cancer, and inversely related to stomach, oesophageal and liver malignancies, although effects were modest. The only robust gradient was found for IQ in relation to skin cancer (HRper one standard deviation advantage in IQ; 95% confidence interval 1.18; 1.13, 1.24; P value for trend across categories: <0.01), which was attenuated but retained statistical significance after adjustment for indices of socioeconomic position across the life course. CONCLUSIONS: In this large cohort of Swedish men followed into middle age, IQ was related to very few of the cancer outcomes under investigation. This indicates that the recent observation that low IQ is related to increased mortality rates may not be generated by an IQ-cancer gradient. Given that the present analyses are among the first to examine these associations, replication is required.

The association of fetal and childhood growth with risk of schizophrenia. Cohort study of 720,000 Swedish men and women.

Previous investigations of the association of schizophrenia with patterns of pre- and post-natal growth have been based on small numbers of cases or have not taken account of the effects of prematurity on birthweight. We investigated the association of fetal growth with schizophrenia in a large cohort of Swedish males and females. We linked data from the Swedish Medical Birth Register (1973-1980), Inpatient and Discharge Register (1988-2002), Military Service Conscription Register (1990-1997), and the Population and Housing Censuses (1970 and 1990). Altogether 719,476 males and females were followed up from the age of 16 for a mean of 9.9 years. There were 736 incident cases of schizophrenia. Even in models that did not control for gestational age there was little evidence of an association between birthweight and schizophrenia (hazard ratio per kg increase in birthweight: 0.90 (95% CI 0.78 to 1.03); the hazard ratio in babies weighing <2.5 kg compared to 3.5-4.0 kg was 1.29 (95% CI 0.85 to 1.96). There was an inverse association of birth length with schizophrenia across the range of birth lengths. Short babies were at an increased risk (hazard ratio per 10 cm increase in birth length: 0.53, 95% CI 0.31 to 0.89 (fully adjusted model)). All associations were little changed when analyses were restricted to term (>36 week gestation) babies. In males, low body mass index and short height at age 18 were associated with increased risk. There is some evidence that patterns of risk in relation to fetal growth differ depending on post-natal growth patterns: the increased risk associated with low body mass index was restricted to long babies who became light adults. The exposures underlying these associations and the biological mechanisms mediating them require clarification.

Is the season of birth association with psychosis due to seasonal variations in foetal growth or other related exposures? A cohort study.

OBJECTIVE: To investigate the association between season of birth and psychosis, and to assess whether any association is caused by seasonal fluctuations in foetal growth or other related exposures. METHOD: Cohort of 747 432 Swedish males and females born between 1973 and 1980 and followed up from 16 years of age to 31 December 1999. Psychiatric admissions were identified using the Swedish Inpatient Discharge Register. The analysis is based on the 696 025 subjects with complete data. RESULTS: A total of 506 (0.07%) subjects developed schizophrenia and 879 (0.13%) non-affective non-schizophrenic psychoses. There was a moderate increased risk of schizophrenia amongst winter births, hazard ratio 1.23 (95% confidence interval 0.96-1.59), but this did not reach conventional levels of statistical significance. There was no association with non-affective psychoses. We found no evidence that associations were confounded by measures of foetal growth or maternal socioeconomic position. There was no evidence that seasonal effects on schizophrenia differed in men and women. CONCLUSION: Season of birth associations with schizophrenia do not appear to be confounded by birth-related exposures.

Association between psychotic disorder and urban place of birth is not mediated by obstetric complications or childhood socio-economic position: a cohort study.

BACKGROUND: Although urban place of birth has been identified as a risk factor for schizophrenia, the extent to which this association is mediated by socially patterned risk factors such as obstetric complications and childhood socio-economic position is unclear. The diagnostic specificity of the association within the clinical psychotic syndromes is also unclear. METHOD: A population cohort of 696025 males and females, born in Sweden between 1973 and 1980 and with linked birth and socio-economic data was followed up from age 16 for up to 9.8 years. Hospitalized cases of schizophrenia and other non-affective psychosis were identified from the Swedish Inpatient Discharge Register. We examined associations of these disorders with a three-level measure of urbanicity of birthplace before and after controlling for measures of foetal nutrition, obstetric complications and level of maternal education. RESULTS: Urban compared to rural birthplace was associated both with increased risk of adult onset schizophrenia (hazard ratio 1.34, CI 0.91-1.96) and other non-affective psychoses (hazard ratio 1.63, CI 1.18-2.26). None of these associations was greatly affected by adjustment for obstetric complications or maternal educational level. In the group of other non-affective psychoses urban-rural differences in disease risk were strongest among those born in the winter months. CONCLUSION: Urbanization of birthplace is associated with increased risk of non-affective psychosis but this is not confined to narrowly defined cases. The magnitude of the association in Sweden is lower than that reported in other studies. Causal factors underlying this association appear to operate independently of risks associated with obstetric complications and parental educational status.