Changes in BMI and waist circumference in Scottish adults: use of repeated cross-sectional surveys to explore multiple age groups and birth-cohorts.

OBJECTIVE

To document changes in body mass index (BMI) and waist circumference (WC) over a 10-year period 1998-2008, in representative surveys of adults.

SUBJECTS

Adults aged 18-72 in the Scottish Health Surveys conducted in 1998, 2003 and 2008 were divided, separately for men and women, into eleven 5-year age bands. 'Synthetic birth-cohorts' were created by dividing participants into thirteen 5-years-of-birth bands (n=20 423). Weight, height and WC were objectively measured by trained observers.

RESULTS

SUBJECTS with data available on BMI/WC were 7743/6894 in 1998, 5838/4437 in 2003 and 4688/925 in 2008 with approximately equal gender distributions. Mean BMI and waist were both greater in successive surveys in both men and women. At most specific ages, people were consistently heavier in 2008 than in 1998 by about 1-1.5 BMI units, and WCs were greater by about 2-6 cm in men and 5-7 cm in women. Greater increases were seen at younger ages between 1998 and 2003 than between 2003 and 2008, however increases continued at older ages, particularly in waist. All birth-cohorts observed over the 10 years 1998-2008 showed increases in both BMI and waist, most marked in the younger groups. The 10-year increases in waist within birth-cohorts (mean 7.4 cm (8.1%) in men and 8.6 cm (10.9%) in women) were more striking than in BMI (mean 1.8 kg m(-2) (6.6%) in men and 1.5 kg m(-2) (6.4%) in women) were particularly steep in older women.

CONCLUSION

People were heavier and fatter in 2003 than those of the same age in 1998, with less marked increases in WC between 2003 and 2008 than between 1998 and 2003. There were proportionally greater increases in WC than in BMI, especially in older women. This suggests a disproportionate increase in body fat, compared with muscle, particularly among older women.