The effect of excess BMI

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) ?

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3 Responses to “The effect of excess BMI”

  1. It’s a new day, it’s a new dawn, it’s a new blog… for me! Says:

    […] The effect of excess BMI « Protons for Breakfast Blog […]

  2. Emma Says:

    I expect that you need to see a more holistic picture here. I’d bet that someone with a BMI of 28 who was really fit and exercised regularly would have a longer life expectancy than someone with a BMI of 24 who never did any exercise. I also think that if you eat a well-balanced diet, but are a bit chubby, you’re probably better off than if you’re someone who maintains a “healthy” weight, but eats no fruit or vegetables.

    Add to that the fact that something like 90% of people who “diet” have regained the weight within 2 years. Is there any evidence about whether “yoyo” dieting is better or worse than staying slightly overweight?

    How many industries can fail 90% of their customers and still have the customers come back a year later to buy more of their products?!

    Since excess BMI affects us as individuals and as a society, and since the existing diet industry is failing 90% of its customers. Perhaps society needs to stop blaming the fat as “lazy, greedy people who need will power” and actually try to understand the real underlying causes. I know a lot of people with BMIs in the 25-35 range who are definitely not lazy or greedy in any other aspect of their lives, nor lacking in will power to succeed at any other goal they set themselves. Telling them that they’re shortening their life expectancy isn’t going to solve the problem either. Not that I know what will!

  3. vapeurs Says:

    Wonderful. This is what I was searching. Thanks.

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