“We knew from previous research that central obesity is bad, but what is new in this research is that the distribution of the fat is very important even in people with a normal weight,” said Dr Francisco Lopez-Jimenez, senior author on the study and a cardiologist at the Mayo Clinic in Rochester, Minnesota. “This group has the highest death rate, even higher than those who are considered obese based on BMI. From a public health perspective, this is a significant finding.”
The study included 12,785 subjects aged 18 years and older from the Third National Health and Nutrition Examination Survey (NHANES III) and provided a representative sample of the United States population. The surveys recorded body measurements such as height, weight, waist circumference and hip circumference, as well as socioeconomic status, comorbidities, physiological and laboratory measurements. Baseline data were matched to the National Death Index to assess deaths at follow up.
Subjects were divided into three categories of BMI (normal: 18.5-24.9kg/m2; overweight: 25.0-29.9kg/m2; and obese: >30kg/m2) and two categories of waist-to-hip ratio (normal: <0.85 in women and <0.90 in men; high: =0.85 in women and =0.90 in men). Analyses were adjusted for age, sex, race, smoking, hypertension, diabetes, dyslipidemia and baseline BMI. Subjects with chronic obstructive pulmonary disease and cancer were excluded.
The mean age of subjects was 44 years old and 47.4% were men. The median follow up period was 14.3 years. There were 2,562 deaths, of which 1,138 were cardiovascular related.
The subjects with normal BMI but central obesity as defined by a high waist-to-hip ratio had the highest cardiovascular death risk and the highest death risk from all causes among the six subgroups. The risk of cardiovascular death was 2.75 times higher and the risk of death from all causes was 2.08 times higher in normal weight obese people as compared with subjects with normal BMI and normal waist-to-hip ratio.
“To our knowledge it is the first study that evaluated nationwide estimates of death in central obesity even in the absence of obesity as measured by BMI,” said Dr Sahakyan, who is a cardiology research fellow at the Mayo Clinic in Rochester. “The high risk of death may be related to a higher visceral fat accumulation in this group, which is associated with insulin resistance and other risk factors, the limited amount of fat located on the hips and legs, which is fat with presumed protective effects and to the relatively limited amount of muscle mass.”
“Many people today know their BMI,” added Dr Lopez-Jimenez. “Our research shows that if a person has a normal BMI, this by itself should not reassure them that their risk for heart disease is low. Where their fat is distributed on their body can mean a lot, and that can be determined easily by getting a waist-to-hip measurement, even if their body weight is within normal limits.”
Dr Sahakyan concluded: “Health professionals need to educate patients about the importance of having a healthy weight and a normal weight-to-hip ratio. Promotion of healthy lifestyle including healthy eating and exercise is perhaps the best strategy.”