Older people with high waist-hip ratios have a higher mortality risk than those with a high body mass index, or BMI, a new study has revealed.
Whereas justifiable attention is given to the increasing problem of obesity in the general population, far less is known about the relationship between obesity and mortality in older people, or how mortality risk should be estimated.
The excess health risks associated with having a high BMI are known to decline with age, yet expert bodies such as the National Institutes of Health and the World Health Organisation have continued to use in older people the same BMI criteria as for other age groups.
The findings confirmed that the current guidelines for BMI-based risk categories overestimate the risks of excess weight in people aged over 75 and are inappropriate for older men and women. This concurs with a previous study that found BMIs of 25-27 not to be a risk factor for all-cause and cardiovascular mortality in those aged 65 and over1.
'An explanation for the lack of a positive association with BMI and mortality at older ages is that, in older persons, BMI is a poor measure of body fat', say the authors. 'The measurement of weight does not differentiate between fat and fat-free mass, and fat-free mass (especially muscle) is progressively lost with increasing age
Waist circumference (WC) has been proposed as an alternate or additional measure of obesity. The study found no association with waist circumference and mortality. The authors continue: 'A limitation of WC alone as a measure is that it takes no account of body composition, whereas WHR is a measure of body shape and to some extent of lower trunk adiposity [abdominal fat].
The authors recommend that the current BMI-based health risk categories to define the burden of disease related to adult overweight and obesity be reviewed, as they are not appropriate for those over 75.
They suggest that WHR should instead be used in this age group because of its positive relation with risk of death, and that attention should also be paid to the problem of underweight in old age.