News Release

Body-mass index above ideal range causes large increase in mortality

Peer-Reviewed Publication

The Lancet_DELETED

A study of around 900,000 adults has revealed a body-mass index (BMI) above the ideal range of 22.5-25 kg/m2 leads to increased mortality rates. Above 25 kg/m2, each extra 5 kg/m2 results in an increased overall mortality of around one third. Moderate obesity (BMI 30-35) is quite common but has only one third the effect on mortality of smoking; while severe obesity (BMI 40-50) has a similar effect to smoking, but is still relatively rare. These are the conclusions of Professor Sir Richard Peto and Dr Gary Whitlock, Clinical Trial Service Unit, University of Oxford, UK, and colleagues from the Prospective Studies Collaboration,* in an Article published Online First and in an upcoming edition of The Lancet.

Generally, BMI is a reasonably good measure of how overweight a person is. It is an established risk factor for various causes of death, and many populations have seen their average BMI rising by a few percent per decade, fuelling concerns about the impact of rising obesity on health. The authors analysed the relationship between BMI and the risk of dying from particular diseases. They used data from 57 prospective studies involving 894,576 participants, mostly in western Europe and North America. The mean age was 46 years and the mean BMI 25 kg/m2, and 61% of participants were men.

The authors found that in both sexes, the mortality was lowest in the BMI range 22.5-25 kg/m2. This means that if a person were 1.70m (5 feet 7 inches) tall, for example, his or her optimum weight would be about 70kg (154 pounds or 11 stone). Each additional 5 kg/m2 translated into the following increases in mortality: overall 30%; heart disease, stroke, and other vascular disease 40%; diabetes/liver disease/kidney disease 60-120%; cancer 10%; lung disease 20%. Moderate obesity (BMI 30-35 kg/m2), which is now common, reduced survival by between two and four years. However severe obesity (40-45kg/m2), which remains relatively rare, reduced survival by eight to 10 years, comparable to the effects of smoking. There was also a higher death rate among those who had a BMI well below the optimum range. This was due mainly to smoking related diseases, however further study is required to fully understand the reasons behind this relationship.

Dr Whitlock says: ''Excess weight shortens human lifespan. In countries like Britain and America, weighing a third more than the optimum shortens lifespan by about 3 years. For most people, a third more than the optimum means carrying 20 to 30 kilograms (50 to 60 pounds, or 4 stone) of excess weight. If you are becoming overweight or obese, avoiding further weight gain could well add years to your life.''**

Professor Peto adds: "This study has shown that continuing to smoke is as dangerous as doubling your body weight, and three times as dangerous as moderate obesity. Changing your diet but keeping on smoking is not the way to increase lifespan. For smokers the key thing is that stopping smoking works.'''**

The authors conclude with some advice echoing the adage 'prevention is better than cure', saying: "In adult life, it may be easier to avoid substantial weight gain than to lose that weight once it has been gained. By avoiding a further increase from 28 kg/m² to 32 kg/m², a typical person in early middle age would gain about two years of life expectancy. Alternatively, by avoiding an increase from 24 kg/m² to 32 kg/m² (ie, to a third above the apparent optimum), a young adult would on average gain about three extra years of life."

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For information regarding the accompanying Comment, please see below.***

For Professor Sir Richard Peto and Dr Gary Whitlock, please contact the Medical Research Council Press Office T) +44 (0) 20 7637 6011 / out of hours call +44 (0) 7818 428 297 E) press.office@headoffice.mrc.ac.uk

For full Article and Comment, please see attached pdf

*Funding for the overall analysis study was provided by the Medical Research Council, the British Heart Foundation and Cancer Research UK supporting the Clinical Trial Service Unit at the University of Oxford.

**These are quotes directly from the authors and cannot be found in the text of the Article

***There is no accompanying Comment with the Article at this stage; but one will be published when the Article appears in The Lancet 28 March print edition.


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