Body mass index and unintentional weight change associated with all-cause mortality in older Australians: the Melbourne Longitudinal Studies on Healthy Ageing (MELSHA)

SIR—Determining the risk of premature death across the spectrum of body mass index ([BMI] defined as weight in kilogrammes divided by height in metres squared) categories is important epidemiological information for public health advocacy and policy, given the projected worldwide increases in overweight (BMI 25 to 29.9) and obesity (BMI 30+) prevalence [1]. This is particularly so for older people because the prevalence of at least overweight is highest among this population subgroup in Australia [2] and in other developed countries [3, 4]; the burden of chronic diseases including diabetes, high cholesterol and high blood pressure increased in recent years markedly for obese and older people (aged 60+ years) [5]; and because of the world’s ageing population [6]. Yet the association between BMI and risk of premature death in older people is far from determined. A systematic review of cohort studies (published up to 1999) in populations aged 65+ years found that either BMI was not a risk factor or low rather than high BMI values increased the risk of all-cause mortality [7]. A more recent systematic review of cohort studies (published up to 2005) in populations aged 65+ years found that overweight was not a risk factor for all-cause mortality and that obesity conferred only a small excess risk (10%) compared to normal weight (BMI 18.5 to 24.9) [8]. Findings from relevant studies published since are also mixed. Most show that all-cause mortality is inversely associated with BMI [9–13] and not significantly associated with overweight or obesity [11, 12]. Others show no association with overweight, but a significant association with obesity [14] and severe obesity (BMI 35+) [3] (although underweight remained the strongest predictor in both studies). The overall body of evidence suggests that low BMI values are stronger predictors of premature death than high BMI values in older people and implies that current worldwide clinical guidelines for optimum body weight for survival (BMI 18.5 to 24.9 for all adults aged 18+ years) may not be valid for this older population subgroup.