More than one in three middle-aged Americans are now in this category,
Whitlock said. “By contrast, weighing twice your ideal weight — say, an
extra 150 pounds — shortens life span by about 10 years,” he added.
This obesity level is still not common, but it equals the known 10-year
reduction in life span caused by smoking. “So, smoking is about as
dangerous as being severely obese, and about three times as dangerous as
being moderately obese,” he said.
The report is published in the March 18 online edition of The
Lancet.
For the study, Whitlock and other members of the Prospective Studies
Collaboration collected data on 894,576 men and women who participated in
57 studies. The people in these studies came primarily from western Europe
and North America. Their average body-mass index (BMI) was 25.
BMI is a calculation that expresses a relationship between height and
weight. People are considered underweight if their BMI is less than 18.5,
normal weight when the BMI is between 18.5 and 24.9, overweight when BMI
is between 25 and 29.9, and obese when BMI is 30 or more, according to the
U.S. National Heart, Lung, and Blood Institute.
The researchers found that men and women whose BMI was between 22.5 and
25 lived the longest. For a person 5 feet 7 inches tall, his or her
optimum weight would be about 154 pounds, they noted.
For those with a BMI over 25, every 10 to 12 pound increase translated
to about a 30 percent increased risk of dying. In addition, there was a 40
percent increase in the risk for heart disease, stroke and other vascular
disease, a 60 percent to 120 percent increased risk of diabetes, liver
disease or kidney disease, a 10 percent increased risk of cancer, and a 20
percent increased risk for lung disease, the researchers reported.
“Obesity causes kidney disease, liver disease and several types of
cancer, but the most common way it kills is by causing stroke and, most
importantly, heart disease. Obesity causes heart disease by pushing up
blood pressure, by interfering with blood cholesterol levels, and by
bringing on diabetes,” Whitlock said.
People who are moderately obese with a BMI in the 30 to 35 range
reduced their life span by two and four years. For those who are severely
obese with BMIs between 40 and 45, their life span was reduced by eight to
10 years. That’s comparable to the effects of smoking, Whitlock said.
In fact, people whose weight was below normal also died earlier, due
mainly to smoking-related diseases, the researchers noted.
“If you are obese and smoke, then, above all else, quit smoking,”
Whitlock said. “If you are obese and don’t smoke, then don’t start, and do
what you can to avoid further weight gain. By avoiding further weight
gain, you may well live a few years longer than you otherwise would do. By quitting smoking, a smoker can expect to gain several extra years of
life — about as many as a severely obese person might gain by shedding
half of his or her body weight.”
Dr. David L. Katz, director of the Prevention Research Center at Yale
University School of Medicine, said this study confirms that the obesity
epidemic is “the clear and present danger many of us knew it to be.”
The association between BMI and mortality has been challenged in the
scientific community, due in part to uncertainty about weight estimates
and debate about measurement methods. “Here we have an emphatic
reaffirmation of the fundamental issue: Overweight and obesity take years
from life,” Katz said.
“We know that, in many ways, BMI is a crude measure of the health risks
associated with obesity, since not all excess body fat is created equal,”
he said. “Weight gained around the middle tends to be most dangerous, so
for those subject to this pattern, risks may indeed be higher than this
study suggests. For those with lower body weight gain, risks may be
lower.”
A study published in the Nov. 13 issue of the New England Journal of
Medicine also found that where weight is centered is a risk factor.
Men with the largest waist circumference had more than double the risk of
death, and women with the largest waist circumference increased their risk
of death by 78 percent.
