As mentioned above, prevalence of obesity is an important factor in influencing prevalence of the metabolic syndrome. The association of central or general obesity and the metabolic syndrome varies with gender (Ho etal., 2001). Distribution of fat influences prevalence of the metabolic syndrome for a given BMI. The NHANES III study showed that prevalence of the metabolic syndrome (defined using the ATP-III criteria) increased from 0.9-3.0 per cent for people with a BMI in the range 18.5-20.9 kg m-2 to 9.6-22.5 per cent for people with a BMI in the range 25.0-26.9kgm-2, depending on gender and ethnicity (St Onge, Janssen and Heymsfield, 2004). The influence of obesity on prevalence of the metabolic syndrome also has been observed in children. A detailed study of 439 obese, 31 overweight and 20 non-obese children and adolescents in the USA found that prevalence of the metabolic syndrome increased with the severity of obesity and around half of the severely obese participants had the metabolic syndrome (Weiss etal., 2004). Data from 12-19-year-old participants in NHANES III showed that prevalence of the metabolic syndrome (using ATP-III criteria modified for age) varied between 0.1 percent for those whose BMI was below the 85th percentile to 29 per cent among those whose BMI was above the 95th percentile (Cook etal., 2003).
The cut-points of the BMI used to replace waist circumference as a proxy for obesity in different populations are likely to vary with age, gender and ethnicity and have not been clearly established. Lower cut-points of the BMI to define obesity have been suggested for Asian populations (WHO Expert Consultation, 2004).
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