Dave Lowe is one of those colleagues who makes working at NPL such a pleasure. Having read my blog about the excess mortality associated with BMIs greater than 25 , he dropped me a line to let me know of a paper in the Lancet. The paper (Body-mass index and cause-specific mortality in 900 000 adults: collaborative analyses of 57 prospective studies) presents its result in quite a technical way but their ‘interpretation’ section reads thus:
Although other anthropometric measures (eg, waist circumference, waist-to-hip ratio) could well add extra information to BMI, and BMI to them, BMI is in itself a strong predictor of overall mortality both above and below the apparent optimum of about 22·5—25 kg/m2. The progressive excess mortality above this range is due mainly to vascular disease and is probably largely causal. At 30—35 kg/m2, median survival is reduced by 2—4 years; at 40—45 kg/m2, it is reduced by 8—10 years (which is comparable with the effects of smoking). The definite excess mortality below 22·5 kg/m2 is due mainly to smoking-related diseases, and is not fully explained.
As I understand it, this is the link between premature death and the BMI at the time of death . So according to this, if I maintain a BMI of 27 ish for the coming years, I appear to be set to cut my life short by about a year. So I can reasonably hope to live to the age of seventy-ish (and so enjoy three years of my pension :-)). But what happens if I shift my BMI back to 25 in 5 years time? Do I then negate the excess risk to which I had exposed myself. The question to which I would like an answer is this.
- What is excess hazard to which I am exposing myself NOW, by having a BMI of 27 at my current age (51) ?