The study by Oxford Brookes University found that the measurement of waistline against height produced a more accurate prediction of lifespan than BMI.
BMI is calculated as a person's weight in kilogrammes divided by the square of their height in metres.
Having a waist no more than half the length of your height can help prevent the onset of conditions like stroke, heart disease and diabetes and add years to life, researchers said.
The study examined data on patients whose BMI and waist to height ratio were measured in the 1980s.
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Twenty years later, death rates among the group were much more closely linked to participants' earlier waist-to-height ratio than their BMI.
By comparing the life expectancies of various groups of people at different waist-to-height ratios, researchers were able to calculate how many years of life were lost as people's waistlines increased.
Dr Margaret Ashwell, whose previous research has suggested that the waist-to-height ratio could be a better tool than BMI for predicting a range of diseases, presented her findings at the European Congress on Obesity in Liverpool.