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 percent relative increase in mortality rate (the number of deaths per 100 older adults per year) in the group sampled. Thus, if the waist-hip ratio rose from 0.8 to 0.9 or from 0.9 to 1.0, it would mean a 28 percent relative increase in the death rate. Put another way, if hip size is 40 inches, an increase in waist size from 32 to 36 inches signaled a 28 percent relative death-rate increase.

The relationship was not graded in men. Instead there was a threshold effect: The rate of dying was 75 percent 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.

The study may have some limitations, the authors noted. For instance, participants' BMI may be underestimated because height and weight were self-reported and older adults tend to report those numbers from their younger, peak years. Also, waist-hip ratios, waist circumference and BMI numbers were based on single measurements, limiting the researchers' ability to gauge how changing body size in old age can affect mortality risk.

Source: University of California - Los Angeles