From February 2017, information about the work of the MRC/CSO Social and Public Health Sciences Unit, University of Glasgow is available and updated on the University of Glasgow website.

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New study finds that individuals identified as obese using body mass index are only associated with an increased risk of death if they are well over the recognised obesity threshold. Two other measurements of body size, waist circumference and waist-hip ratio, may provide a better reflection of the mortality risks of obesity.

The relationship between body size and mortality in the Scottish population

posted on: Oct 11, 2010

Individuals identified as obese using body mass index are only associated with an increased risk of death if they are well over the recognised obesity threshold. Two other measurements of body size, waist circumference and waist-hip ratio, may provide a better reflection of the mortality risks of obesity.

Joel Hotchkiss and Alastair Leyland made these findings at the MRC/CSO Social and Public Health Sciences unit when they examined the association between body size and mortality in the Scottish population over a 12-year period. The research, published this week in the International Journal of Obesity, was funded by the Chief Scientist Office of the Scottish Government Health Directorate within a programme funded by both the Medical Research Council and the Chief Scientist Office.
 
The Scottish Health Surveys are representative surveys of the Scottish population that anonymously record information on participants’ health, their lifestyle choices and medical measurements. The majority of participants in the 1995, 1998 and 2003 surveys had consented to their information being linked to death records. Work by the Information Services Division of National Health Service Scotland made it possible to follow 20,000 Scots for up to 12 years; 1280 had died by December 2007. The association between body size and the likelihood of dieing during the follow-up period could then be examined while adjusting for age, gender, alcohol consumption and smoking behaviour.
 
Three measures of body size, or obesity, were investigated namely body mass index, waist circumference and waist-hip ratio. An increased mortality risk was associated with a body mass index greater than 40kg/m2, higher than the threshold for obesity which is generally considered to be 30kg/m2. A low body mass index, less than 18.5kg/m2, was also associated with an increased likelihood of death – something identified in other studies. Waist circumference and waist-hip ratio identified an increased risk of death amongst those individuals above the widely accepted thresholds for obesity. This may reflect the ability of these two measurements to summarise the amount of abdominal fat a person has. A large quantity of such fat is believed to be particularly detrimental to health, especially in relation to cardiovascular disease. Body mass index not only doesn’t distinguish how fat is distributed but also is known to misclassify many individuals as overweight or obese.