Evidence that, even though you're not getting taller anymore, the pelvis ("hipbones") does continue to widen as people advance in age from 20 years to 79 years has been found in a new study.
The findings also oppose the established view that skeletal enlargement anywhere in the body stopped by age 20.
"I think it's a fairly common human experience that people find themselves to be wider at the age of 40 or 60 then they were at 20," said Laurence E. Dahners, senior author of the study and a professor in the Department of Orthopaedics in the UNC School of Medicine. "Until recently we assumed that this was caused simply by an increase in body fat.
"Our findings suggest that pelvic growth may contribute to people becoming wider and having a larger waist size as they get older, whether or not they also have an increase in body fat," Dahners said.
The pelvic width of the oldest patients in the study was, on average, nearly an inch larger than the youngest patients. This one-inch increase in pelvic diameter, by itself, could lead to an approximately three-inch increase in waist size from age 20 to age 79. If the rest of the body is widening commensurately, this might account for a significant portion of an increase in body weight of about one pound a year that many people experience during the same period, Dahners said.
In particular, the fact that the pelvic inlet also widened is evidence of true pelvic growth rather than simple appositional bone formation, Dahners said. The pelvic inlet would be smaller if appositional bone formation were taking place, he said.
The study was recently published in the Journal of Orthopaedic Research.