"We have now found in African-American women what has been found in other populations -- that the risk of death goes up incrementally with increasing BMI [body mass index] over 25," says researcher Julie R. Palmer, ScD, professor of epidemiology at Boston University.
BMI is a measure of body fat. A BMI between 18.5 and 24.9 is termed healthy.
The new finding refutes previous data that suggests that the risk of weight-related death in African-Americans is increased only at very high BMI levels, such as 35 and up. A BMI of 30 or higher is obese.
Palmer's study found the risk became significant at 27.5. For example, that is the BMI of a woman 5 feet 4 inches tall who weighs 160 pounds.
A big waist, over 35 inches, also boosts risk, she says. ''Regardless of BMI, having a large waist size, which is an indicator of carrying around excess abdominal fat, is related to having an increased risk of death."
The study is published in The New England Journal of Medicine. The results are based on follow-up of women who were part of the ongoing Black Women's Health Study.
The study results, Palmer says, suggest that ''this is just one more reason to maintain a healthy adult weight." To have a BMI of 24.9, a woman who is 5 feet 4 inches tall, for example, would have to weigh 145 pounds.
Tracking Risks of Obesity
The ongoing Black Women's Health Study includes 59,001 African-American women from all parts of the U.S. Women enrolled in the study in 1995, when they were age 21 to 69. They answer questionnaires every two years.
For this research, Palmer and her team focused on 33,916 women who had never smoked. All were free of cancer and heart disease at the start of the study.
They gathered the women's height, weight, and waist circumference in inches at the beginning of the study. The information was self-reported.
The women also gave information on their exercise habits, education, alcohol intake, and provided other data.
The researchers looked at the National Death Index, trying to find women who had not returned the 2009 questionnaire and were not known to have died.
They tracked down the cause of death from the index or death certificates. They grouped causes of death as cardiovascular, cancer, or other.
Through 2008, the researchers found 1,773 deaths; 770 of these were among the 33,916 nonsmokers they were studying.They took into account such factors as age, physical activity, and alcohol intake. They found that the risk of death from any cause rose as the BMI rose.
''The link became significant when it got to 27.5," she says. For those with BMIs of 27.5 to under 30, the increased risk was 31%.
The risk was highest for heart disease. Women with a BMI of 25 to 29 had a two times higher risk of death from heart disease as normal-weight women. Those with a BMI of 30 or higher had three times the risk.
No significant link was found between BMI and risk of death from cancer.
Waist Size and Health Risks
Next, the researchers focused on the non-obese women. They compared those with large waists (above 35 inches) and those with smaller waists.
"The women in the largest group -- 35 inches or higher -- had a 50% increased risk of dying compared with those not obese with a waist circumference less than 35 inches," Palmer says.
The waist size reflects the amount of abdominal fat. Fat inside of the abdomen that surrounds organs is considered more metabolically active. Too much of this type of fat is considered hazardous to long-term health.
In obese women, she says, they found no effect of waist circumference. She suspects that the amount of fat they have, wherever distributed, is enough to be hazardous.
Obesity Task Force
The National Medical Association, composed of African-American doctors, is aware of the problem. It launched an obesity task force earlier this year, according to Cedric M. Bright, MD, the association's president.
"African-American women have the highest rates of obesity and this directly correlates to other [coexisting] conditions like diabetes, hypertension, certain cancers, heart attacks and strokes," he says in a statement. "Unfortunately, the epidemic of obesity in women is often passed on to their children and families."
The task force is bringing together doctors, surgeons, nutrition experts, and fitness experts who are helping to shape an action plan, Bright says. It will develop a comprehensive approach to combating obesity in African-Americans.
According to the National Medical Association, African-Americans, especially women, are 1.5 times as likely to be obese as non-Hispanic whites.