Discussion
obese, non-cancer, cancer, Deaths, overweight, adiposity, weight loss
OBESE, CVD, CANCER, ADVERSE EFFECTS, ADIPOSITY
In this cohort of more than 18,000 relatively healthy older adults followed for almost 7 years, the principal finding was that the lowest all-cause and cardiovascular mortality occurred in men and women whose BMI and waist circumference was substantially higher than considered normal in current healthy weight guidelines. In men, the relationships were U-shaped with the highest mortality risks amongst those at the bottom and the top of the distribution. In women the increased all-cause and cardiovascular mortality risks were largely confined to the highest BMIs and waist circumferences. The U-shape relationship between mortality and BMI was stronger than the relationship with waist circumference. Amongst cause-specific mortality risks, body size parameters showed a weak relationship to cancer mortality and did not appear to explain the increased mortality amongst underweight individuals. Deaths from causes other than cancer or CVD were increased predominantly in those who were underweight.These findings generally support the findings of a recent meta-analysis relating BMI to all-cause mortality in older populationsThe principal sex differences were seen in the relationships between all-cause and cardiovascular mortality. In men, but not women, there was an increased risk of mortality amongst those at the lowest end of BMI and waist circumference. This led to a substantially greater U-shaped relationship in men than in women, particularly regarding BMI, and this relationship persisted after adjustment for multiple confounding factors. The increase in mortality from non-cancer non-cardiovascular causes amongst those with low BMI or waist circumference may reflect the impact of frailty and prefrailty in this population.The stronger relationship between BMI and mortality compared to waist circumference and mortality was unexpected. While BMI is the most commonly used clinical and population measure of body size, it is only a rough guide to body fatness. Waist circumference better reflects visceral adiposity which has been positively and significantly associated with a higher risk of all-cause mortality in younger populationsThe relationship between body size and health is relevant to the advice given by clinicians and public health spokespeople who commonly provide a strong recommendation to overweight or obese patients to lose weight to reduce their future risk of CVD and cancer. Our findings add to the mounting evidence that the current ‘healthy weight range’ may not be suitable for older adults and strong steps to encourage weight loss in those moderately overweight or obese requires further evaluation. Nor is there a strong indication from these results for clinicians to rely on waist circumference rather than BMI when providing health advice. However, despite the findings of this study, overweight and obesity have various other negative health consequences that must also factor into the advice provided by cliniciansThis study also has some potential limitations that require discussion. Firstly, the results of this study are most relevant to a largely Caucasian population drawn from communities with access to universal healthcare, as reflected by the high utilisation of statins and antihypertensive drugs. The high frequency of preventive medication might have blunted some adverse effects of overweight and obesity. Secondly, the population studied was drawn from volunteers for a clinical trial who are likely to have been more attentive to maintaining a healthy lifestyle that others in the community. The results may have limited relevance for South Asian, Chinese or Japanese adults where the population distributions of BMI and waist circumference may differ