Body Mass Index (BMI) is the ratio between height and weight, and is typically used to gauge whether  person is underweight, overweight, or within a normal weight range. Preethi Srikanthan, from the University of California/Los Angeles (USA), and colleagues analyzed data from the MacArthur Successful Aging Study, a longitudinal study of high-functioning men and women, ages 70-79 years at the study’s start.  The team examined 12-year, all-cause mortality risk by BMI, waist circumference, and waist-to-hip circumference ratio (WHR).  To gauge obesity in the elderly population, they found the ratio of waist size to hip size to be a superior indicator to BMI. The researchers found no association between all-cause mortality and BMI or waist circumference; the link was only with waist-hip ratio. In women, each 0.1 increase in the waist-hip ratio was associated with a 28% relative increase in mortality rate in the group sampled.  For example, if the waist-hip ratio rose from 0.8 to 0.9 or from 0.9 to 1.0, it would mean a 28% relative increase in the death rate; in other words, if hip size is 40 inches, an increase in waist size from 32 to 36 inches corresponded to a 28% relative death-rate increase. For men, however, a threshold effect was observed: The rate of dying was 75% higher in men with a waist-hip ratio greater than 1.0 — that is, men whose waists were larger than their hips — relative to those with a ratio of 1.0 or lower. There was no such relationship with either waist size or BMI.  "Basically, it isn't BMI that matters in older adults — it's waist size," remarked Dr. Srikanthan, continuing that “this is one of the first studies to show that relative waist size does matter in older adults, even if BMI does not matter."