Obesity is considered the leading preventable cause of death worldwide — until you reach old age, that is. Though obesity increases the risk of an early death, shaving an average of six to seven years off a person's lifespan, Tel Aviv University researchers have found that this trend may reverse itself after the age of 85.
In these people, excess fat seems to have a "protective" effect, decreasing the risk of death when compared to those who are considered at a normal body weight.
When we reach a very old age, some of the factors that affect mortality in younger people may no longer be significant, explain Prof Jiska Cohen-Mansfield and Rotem Perach of the Herczeg Institute on Ageing and the Sackler Faculty of Medicine.
Heavier people have lower rates of osteoporosis, which could decrease incidences of falls and subsequent injury. Obesity could also provide excess energy storage in times of trauma or stress, or prolong the period of weight loss caused by a decrease in appetite, a common occurrence as people near death.
This research was recently published in the Journal of Aging Research.
The survival effect
Research has consistently shown that people who are underweight in their old age have a higher mortality risk. But until now, the protective impact of obesity on mortality in this same age group has been unexplored.
The study was based on data collected as part of the Cross Sectional and Longitudinal Aging Study (CALAS), which included 1 349 people between the ages of 75-94. Participants were asked basic questions about their height and weight, age, gender, family, education, socioeconomic status, and smoking history.
Two decades after the data was first collected, the researchers completed a mortality analysis on the original sample. During the course of these 20 years, 95% of the participants had died, leaving 59 subjects still living.
Obesity continued to be a predictor of death for those aged 75-84, notes Professor Cohen-Mansfield. But past the age of 85, participants who were in the obese category were not only at lower risk of death than their underweight peers, but also appeared to be less at risk than those who had a normal weight as well.
There is a "selective survival" rate at play, say the researchers. Often, obese people die early in life due to obesity-related illnesses. So those who survive to old age could simply be more resilient. The same principle may be true of other factors, such as smoking.
Life at a cost
Though the findings are surprising, Professor Cohen-Mansfield points out that obesity only has a protective effect when it comes to mortality. Quality of life, she warns, is another matter. "Though obese people over the age of 85 may be less at risk of death, they may suffer more from obesity-related illnesses," she says. "There are other factors to consider, such as pain, multiple ailments, and mobility."
(EurekAlert, February 2012)