It has recently been discovered that obesity is a lot more deadly than previously thought. According to a study funded by the Robert Wood Johnson Foundation, obesity rates have accounted for 18 percent of deaths among black and white Americans between the ages of 40 and 85. This finding challenges the previously accepted number of five percent that has been widely accepted by scientists.

“Obesity has dramatically worse health consequences than some recent reports have led us to believe,” says first author Ryan Masters, who conducted the research as a Robert Wood Johnson Foundation Health & Society Scholar at Columbia University’s Mailman School of Public Health. “We expect that obesity will be responsible for an increasing share of deaths in the United States and perhaps even lead to declines in U.S. life expectancy.”

Although there have been signs of a decline in obesity among some groups of young people, rates continue to stay near historic highs. For most adults and children that are already obese, the condition will likely persist, causing damage over the course of their lives.

The rising toll of obesity among older Americans is already evident. Dr. Masters and his colleagues documented the increasing effect on mortality in white men who died between the ages of 65 and 70 in the years 1986 to 2006. Grade one obesity, body mass index of 30 to less than 35, accounted for about 3.5 percent of deaths in those born between 1915 and 1919. Among those born 10 years later, it accounted for about five percent of deaths. Another 10 years later it accounted for about seven percent of deaths.

When the obesity epidemic hit in the 1980s, it hit all age groups, which means older Americans have lived through it for only a short period of time. However, younger groups will be exposed for to it for a much longer period.

“A 5-year-old growing up today is living in an environment where obesity is much more the norm than was the case for a 5-year-old a generation or two ago. Drink sizes are bigger, clothes are bigger, and greater numbers of a child’s peers are obese,” explains co-author Bruce Link, professor of epidemiology and sociomedical sciences at Columbia University’s Mailman School of Public Health. “And once someone is obese, it is very difficult to undo. So it stands to reason that we won’t see the worst of the epidemic until the current generation of children grows old.”

This study is the first to account for differences in age, birth cohort, sex, and race in analyzing Americans’ risk for death from obesity.

“Past research in this area lumped together all Americans, but obesity prevalence and its effect on mortality differ substantially based on your race or ethnicity, how old you are, and when you were born,” says Dr. Masters. “It’s important for policy-makers to understand that different groups experience obesity in different ways.”