Background: Adiposity and health risks are better indicated by waist circumference than body mass index (BMI). Patterns of change with age are incompletely documented.
Methods: Adults aged 18-92 years in the Scottish and English Health Surveys of 1994-96 and 2008-10 were divided into fifteen 5-year age bands. Sex-specific prevalences of overweight/obesity and of increased/high waist circumference against age were compared using analysis of covariance.
Results: Data available for 7932 Scottish and 55 925 English subjects in 1994-96, and for 27 391 Scottish and 30 929 English in 2008-10, showed generally similar patterns of change in the two countries. Prevalences of both elevated BMI and waist circumference rose with age for longer in 2008-10 than in 1994-96, reaching higher peaks at greater ages, particularly among men. Between 1994-96 and 2008-10, maximum prevalences of BMI>30 increased from 25 to 38% (larger increases in men than women), reaching a peak at age 60-70 years in both sexes. This peak prevalence was 5-10 years later than in 1994-96 for men and remained unchanged for women. Between 1994-96 and 2008-10, maximum prevalences of high waist circumference (men>102 cm, women>88 cm) increased from 30 to -70% in both sexes, peaking in 2008-10 at ages 80-85 years (men) and 65-70 years (women). In 2008-10, proportions of adults with 'normal' BMI (18.5-25) fell with age to 15-20% at age 60-70 years (men) and 75 years (women). Among all those with BMI=18.5-25, aged>65 years, the proportions with unhealthily elevated waist circumference were 30 (men>94 cm) and 55% (women>80 cm).
Conclusions: Almost 40% of men and women are now becoming obese. People are growing fatter later in life, with waist circumference rising more persistently than BMI, which may indicate increased loss of muscle mass and sarcopenia in old age. Among older people, few now have 'normal' BMI, and of these up to half have elevated waist circumference, raising questions for the suitability of BMI as a measure of adiposity in this age group.