Nov. 6, 2007 -- New research from the CDC confirms that people who carry a few extra pounds have a lower risk of death than those who are normal weight, extremely underweight, or obese.
The study updates and expands a headline-making study from 2005, which first suggested a survival advantage for people considered overweight, but not obese, according to government standards.
Using additional mortality data with longer follow-up, the newer analysis examines death risk by specific cause.
Compared with people who fell into the normal-weight category, being obese was associated with an increased risk of death from cardiovascular disease, diabetes, and cancers that have been linked to obesity, such as colon, breast, esophageal, uterine, and ovarian cancers.
Obesity was not associated with an increased risk of death from other cancers.
Being underweight was linked to an increased risk of death from non-cancer and non-cardiovascular causes.
The study is reported in this week's Journal of the American Medical Association.
Body Weight and Death
CDC senior research scientist Katherine Flegal, PhD, who led the study team, tells WebMD that the analysis presents a more nuanced picture of the relationship between body weight and mortality.
"I don't think this paper or the previous one can be generalized to make sweeping statements," she says. "There is nothing here that should change public health messages about overweight and obesity."
But she adds that in both studies, being modestly overweight was associated with an overall decrease in excess mortality.
In the newly reported study, CDC researchers used data from the National Health and Nutrition Survey (NHANES) to link deaths from specific causes to body weight, as measured by body mass index (BMI), which defines fatness and thinness based on height and weight.
A 5-foot-7-inch person is considered underweight with a BMI of 18.5, meaning that they weigh 118 pounds or less. Using the BMI measurement, the same person would be considered normal weight at a weight of 119 to 159 pounds, overweight at between 160 and 191 pounds, and obese at 192 pounds or more.
In the 2005 study, Flegal and colleagues speculated that carrying extra weight may not be as deadly as it once was because of better management and treatments for obesity-related diseases like diabetes and heart disease.
BMI, Age, and Mortality
But JoAnn Manson, MD, who is chief of preventive medicine at Boston's Brigham and Women's Hospital, says that doesn't mean carrying a few extra pounds has no negative impact on health.
"We should not become more complacent about overweight and obesity because of these findings," she tells WebMD.
"The big picture of health extends far beyond mortality. We know that having a BMI in the overweight range is associated with many adverse health effects, including an increased risk for diabetes, hypertension, and cardiovascular disease as well as decreased physical function."
And because most deaths occur among the elderly, the findings may have more relevance to people in their 70s and 80s than to younger people.
"We know that BMI is a less reliable measure of body fatness in older people, due to loss of muscle mass and weight loss due to chronic disease," Manson says.
There is also some suggestion that carrying some extra weight is associated with a survival advantage in elderly people with chronic disease. The thinking is that these people have more muscle mass and nutritional reserves that can help them fight illness and regain their strength after hospital stays.
But Manson dismisses the idea that obesity is less dangerous for older people than younger ones.
"Obesity has a major impact on mortality at all ages," she says.