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Objectives: To determine the mean body mass index (BMI, kg/m(2)) and prevalence of low weight (BMI<20) and obesity (BMI ≥ 30) in 3 population-based surveys, and to describe the longitudinal changes during 1994-2008 in mean BMI, and the prevalence of low weight and obesity., Setting: A population study in Tromsø, Norway., Participants: A total of 29,688 different participants in 1 or more of 3 surveys (1994-1995, 2001-2002 and 2007-2008). Longitudinal analyses comprised 9845 participants aged 25-69 in 1994 who participated in the 1994-1995 and 2007-2008 surveys and 4202 men and women who participated in all 3 surveys., Outcome Measures: Mean age-specific and sex-specific BMI, prevalence of low weight and obesity, and changes in BMI and prevalence of low weight and obesity during 1994-2008, according to sex and birth cohort., Results: The age-adjusted (ages 30-84) prevalence of obesity increased from 9.8% and 11.8% in men and women, respectively, in 1994-1995 to 20.9% and 18.5%, respectively, in 2007-2008. The increase in mean age-adjusted BMI was stronger from 1994-1995 to 2001-2002 than from 2001-2002 to 2007-2008. Longitudinal results confirmed that the change in BMI from 1994-1995 to 2001-2002 was larger (0.9 kg/m(2) (95% CI 0.8 to 1.0) in men and 1.3 kg/m(2) (95% CI 1.2 to 1.4) in women) than from 2001-2002 to 2007-2008 (0.2 kg/m(2) (95% CI 0.1 to 0.3) in men and women). The most recently born had the largest increase (p<0.001)., Conclusions: The mean BMI and the prevalence of obesity are still increasing in Tromsø, and the increase is strongest in the youngest age groups. However, the increase in BMI was less marked in the last period (from 2001-2002 to 2007-2008) than in the first period (1994-1995 to 2001-2002)., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Background: Abdominal obesity increases all-cause mortality and is a risk factor for a number of diseases. There are few population-based studies of the longitudinal changes of abdominal obesity. Methods: Based on data from the Tromsø Study, we studied gender- and age-specific mean waist circumference and prevalence of abdominal overweight and abdominal obesity in two surveys in 1994-1995 (Tromsø 4, 6812 men and women aged 25 to 84) and 2007-2008 (Tromsø 6, 12,493 men and women aged 30 to 87). Furthermore, we describe the longitudinal changes of waist circumference and abdominal obesity during 13 years in 3144 subjects (aged 25-69 in 1994) who attended both surveys. Results: Cross-sectional analyses found a higher mean waist circumference in men than women and a direct relationship with age in both men and women in both Tromsø 4 and in Tromsø 6. As the WHO cut-off points for abdominal obesity are gender-specific, however, the prevalence of abdominal obesity was lower in men than in women. In 2007-2008, approximately 37 and 55% of men and women, respectively, were classified as abdominally obese. Thirteen years before, in 1994-1995, the corresponding figures were 20 and 35%. Longitudinal analyses of changes during the 13-year period clearly demonstrated that mean waist circumference increased in all examined birth cohorts in both men (mean change 6.1 cm) and women (mean change 8.4 cm), but increased more markedly the younger the subjects were. The prevalence of abdominal obesity in men aged 25-34 increased from 5% in 1994 to 31% 13 years later. The prevalence of abdominal obesity more than doubled among both men and women. Conclusions: The increasing mean waist circumference is of concern. There is a need for further longitudinal studies of the changes in waist circumference. [ABSTRACT FROM AUTHOR]