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Tuesday, March 17, 2015

Getting old and fat ~ no problem!

Growing old and fat ~ no problem

In today’s obesocentric (a new word I’ve coined) world, there are certain things that are given. These are the immutable facts about obesity. One of them is that the link between obesity, as measured by Body Mass Index (BMI = kg/m2), is U shaped. Over the range corresponding to desirable weight (BMI =20 to 24.99), there is no relationship between BMI and mortality or morbidity. Below 20, there is a rise in the risk of mortality as one gets skinnier. Above 24.99, mortality rises as BMI increases and it soars when obesity exceeds 30. No matter where you look, this is a given. It’s on the WHO website. It’s in your pharmacy window. It’s in schools, in textbooks and its like the boiling point of water, a given, never to be challenged.

Recently, in writing my new book on obesity, I re-discovered a set of data that was 30 years old. The data were published in a Working Party Report of the Royal College of Physicians of London in 1983[1]. It looked at the association between mortality and BMI over decades of age. Among 20 and 30 year olds, the rise in mortality with increasing BMI was quite dramatic above25. So far so good. Among 40 and 50 year olds, we begin to see the emergence of a U shaped curve, rising at both low and high BMI values. However, among 60 year olds, whereas BMI cause rising mortality at very low values, there was no relationship between BMI and mortality above a BMI value of 20. Of course, death rates rose with age but the pattern of mortality with BMI was very much influenced by age.

The subject has recently been revisited through a systematic review and a meta-analysis[2]. A total of 564 publications were identified in the literature based on key words of which 394 were rejected because of a focus on specific patient groups or non-human studies. Of the remaining 170 papers, a further 150 were excluded because they did not provide two or more age comparisons. That left 20 papers of which 13 were US based, 2 were Finland and Taiwan based and 1 each were from Germany, India and Japan. The increase in the risk of mortality with a BMI greater than 24.9 kg/m2   was assessed for decades of age. Averaging the values for men and women, the increased mortality risk with elevated BMI was 60% among those aged less than 35. That figure the fell progressively: 40% among thev35-45 year olds, 355 for 45-55 year olds, 28% among 55-65 year olds, 20% among the 65 to 75 year olds and a mere 11% in those aged above 75 years. The studies all controlled for the possibility of smoking or a pre-existing illness (e.g. high blood pressure or diabetes) being statistically confounding factors. However, the paper reports that this statistical control had no effect on the outcome. Basically, each increasing decade of life above 35 years of age reduced BMI related mortality by 10%.

Writing as a pensioner, a grandfather and a 67 year old, I say YIPPEE. But my GP doesn’t know this nor does my friends cardiologist and so we grey-heads are demonized unnecessarily by medics into being of adequate BMI. Of course, we do benefit from cardiovascular fitness so a good walk during the day when all the younger folk who kindly earn our pension, work away in a stress-filled environment increasing their BMI mortality risk, is a good idea.

Why does this obesocentric world choose to ignore such data? The answer, it seems to me, is that the simpler the message, the easier is the public health communication. So, they don’t complicate it by absolving older folk from the curse of BMI related mortality. And of course there is the other issue of the obesity paradox[3]. It gets even messier but I love it, the truth, that is!!!

[1] Royal College of Physicians Working Group on Obesity (1983) Journal of the Royal College of Physicians London 17:3-58
[2] Wang Z (2015) Obesity Research & Clinical Practice, 9:1-11
[3] BMI, Obesity & mortality: three grand challenges. Gibneyonfood, December 15th, 2014

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