Recently, scientists from the Centers for Disease Control and Prevention and other researchers surprised just about everyone by reporting that the health and mortality risks associated with being overweight or obese actually diminished with age. But as hearty eaters everywhere breathed a collective sigh of relief, Ryan Masters, PhD, a sociologist and Robert Wood Johnson Foundation Health & Society Scholar (2011-2013), thought the study findings deserved a second look.
“The research showing a survival advantage for older people who were obese just did not sync with other reports on the long-term effects of diabetes, hypertension, heart disease, and other illnesses linked to being overweight or obese,” said Masters, echoing the concerns expressed by many health experts who reviewed the obesity/mortality advantage research.
In an attempt to explain the obesity/mortality paradox, the researchers suggested that the extra weight gave older adults more energy during illness or provided additional protection during falls. From Masters’ perspective, these explanations did not fully account for the supposed longevity advantage.
Masters, a demographer, decided to conduct his analysis from a different point of view. “After examining the demographic characteristics of the population sample used in the original research, I was sort of flabbergasted,” he said. “The study that reported the paradox used a random, household-based sample of people between the ages of 18 and 84. The problem is that selecting study subjects in this way assumes that the age they were included in the study did not matter.”
Survival of the Fittest
“The fact is that whenever you gather supposedly randomized survey data, you are already selecting to some degree,” Masters explained. In simpler terms, the mortality/obesity advantage research was based on samples of people selected by household. Age, weight and health status were then recorded. The data did not account for the former residents of each household who may have died from the health effects of obesity. Nor did it measure the health of individuals over the life course.
For these reasons, Masters said, “the survey was actually highly selective. When people who are obese live to an advanced age, it probably indicates that they have other significant health advantages.”
An Effect Similar to Smoking
Masters reported his findings in the article, “Obesity and US Mortality Risk Over the Adult Life Course,” published in the American Journal of Epidemiology (February 3). His team collected data from 19 cross-sectional segments of the National Health Interview Study (1986-2004), along with data from the National Death Index (2006) and used Cox regression analysis.
The toll obesity takes on the body is similar to the effects of tobacco use.”
Rather than looking at study subjects as one age group, Masters separated them into groups spanning ten years each. “We argue that the existing results were derived from biased estimates of the obesity-mortality relationship because the models used in the original study failed to account for confounding influences from respondents' ages at the time they entered the survey cohort. We found that increased mortality risk from being overweight or obese compounds as people grow older [though it’s lower for men].”
For women with class-one, low level obesity (a BMI of approximately 30), Masters and co-authors Daniel Powers and Bruce Link, PhD, program co-director at the Columbia University Health & Society Scholar site, reported no increased mortality risk at age 35, but an increased risk of 15.4 percent by age 45. The risk increased to 39.2 percent at age 55 and 53.5 percent at age 65. By age 85, obese women had an increased risk of dying of 79.4 percent.
For men, they also found that class-one obesity had no effect on mortality at age 35, but by age 45 the mortality risk increased to 10.3 percent. The risk reached 25.3 percent by age 55 and 39 percent by age 65. The accumulated risk was 52 percent greater for obese men by age 85.
Perhaps the most important message in Masters’ findings is that the toll obesity takes on the body is strikingly similar to the cumulative effects of tobacco use. “Over the life course, the health and mortality risk factors connected with obesity accumulate," he said. The bottom line is, the sooner you slim down the better, but after a certain age, the damage obesity causes cannot be completely reversed.