Central Obesity May Raise Mortality Risk in Normal-Weight Individuals

Risk for mortality appeared to be higher in people with central obesity who otherwise had a normal weight, as compared with people with overweight or obesity as defined by BMI, according to new data.

“Our analyses of data from a large cohort of the NHANES (National Health and Nutrition Examination Survey) III participants show that normal-weight U.S. adults with central obesity have the worst long-term survival compared with participants with normal fat distribution, regardless of BMI category, even after adjustment for potential mediators,” researchers wrote in the Annals of Internal Medicine.

There are conflicting data on how measurements of obesity such as BMI or waist-to-hip ratio impact total and cardiovascular (CV) mortality, according to background information in the study.¹

To learn more, Francisco Lopez-Jimenez, MD, MS, from the division of cardiovascular diseases at Mayo Clinic in Rochester, Minnesota, and colleagues compared differing patterns of adiposity and its effects on total and CV mortality risk.

Data from the Third National Health and Nutrition Survey (NHANES III) were used because hip circumference was not obtained in the more recent 1999 to 2010 NHANES survey, the researchers noted.

According to the data, 16 124 adults had waist-to-hip ratio measurements. After excluding those with a very low BMI and history of non-skin cancers, the cohort was composed of 15 184 participants.

Patient data were linked to the National Data Index for mortality information with specific ICD-9 and ICD-10 codes to identify those with CV-related deaths. 

Of the participants included in the study, mean age was 45 years and 52.3% were women. Additionally, 39.9% had a normal BMI, 34.6% were overweight, 25.1% were obese, and 70.2% had central obesity based on the World Health Organization (WHO) criteria using waist-to-hip ratio.¹

Interestingly, when using WHO central obesity criteria based on waist circumference, only 28.9% were considered centrally obese, the researchers noted.¹

During a mean follow-up of 14.3 years, there were 1404 CV-related deaths and 3222 deaths overall. Multivariable Cox proportional hazards analysis indicated that waist-to-hip ratio was associated with higher mortality risk compared with BMI. 

They researchers found that men with normal weight but central obesity had a higher total mortality risk. Specifically, compared with a man with a similar BMI without central obesity, normal weight and central obesity was associated with an 87% higher mortality risk (hazard ratio [HR]=1.87; 95% CI, 1.53-2.29).¹

Furthermore, men with normal BMI and central obesity still faced a higher higher mortality risk, as compared with men without central obesity who were considered overweight (HR=2.24; 95% CI, 1.52-3.32) or obese (HR=2.42; 95% CI, 1.30-4.53).¹

With respect to women, those with normal BMI and central obesity had a 48% higher total mortality risk compared with those with a similar BMI without central obesity (HR=1.48; 95% CI, 1.35-1.62).

Similarly, total mortality risks were 32% (HR=1.32; 95% CI, 1.15-1.51) and 40% higher (HR=1.40; 95% CI, 1.27-1.54) compared with obese and overweight women without central obesity, respectively.¹

Also, CV mortality risk was higher in both men and women with normal weight and central obesity compared with those with similar BMI and no central obesity (HR=1.78; 95% CI, 1.23-2.57 for men and HR=2.25; 95% CI, 1.66-3.05 for women).¹

The researchers provided several possible explanations for their findings.

First, they noted that central obesity measured by waist-to-hip ratio is associated with an adverse metabolic profile. In particular, insulin resistance, inflammation, dyslipidemia, and hypertriglyceridemia are associated with increasing visceral fat.

Second, the researchers noted that those categorized as obese or overweight according to BMI could have subcutaneous fat in their hips and thighs, which has been associated with more favorable metabolic profiles.  

“What it means is that just having a normal weight (especially in older adults) doesn’t mean they might not be at high cardiovascular risk,” study researcher Michael D. Jensen, MD, also from the Mayo Clinic, wrote in an email to Endocrinology Advisor.

“If physicians have the capacity to measure waist circumference, it will help them identify patients who need further screening. The main risk factors still apply (smoking, cholesterol, HDL cholesterol, triglycerides, blood sugar, and blood pressure). It’s just that those with elevated waist circumferences are more likely to have abnormalities in these risk factors than those with low/normal waist circumferences. We can be more efficient in deciding who to perform laboratory screening tests on if we measure waist circumference,” Dr Jensen added.

In an accompanying editorial, Paul Poirier, MD, PhD, of the Institut Universitaire de Cardiologie et de Pneumologie de Québec in Quebec, Canada, discussed these findings.

“The long-term deleterious consequences of excess adiposity are marked and important. Although the utility of BMI has been borne out in epidemiologic studies, there are limitations to using BMI alone to assess adiposity in clinical practice,” Dr Poirier wrote. 

Dr Poirier also highlighted that BMI does not take into account fat mass vs lean mass and that trying to identify people at higher CV risk by BMI alone may not be adequate.² 

The study was funded by the National Institutes of Health, the American Heart Association, European Regional Development Fund, and the Czech Ministry of Health. Several researchers reported financial disclosures. See the study for a full list.

References

1. Sahakyan KR, Somers VK, Rodriguez-Escudero JP, et al. Normal-Weight Central Obesity: Implications for Total and Cardiovascular Mortality. Ann Intern Med. 2015;doi:10.7326/M14-2525.
2. Poirier P. The Many Paradoxes of Our Modern World: Is There Really an Obesity Paradox or Is It Only a Matter of Adiposity Assessment? Ann Intern Med. 2015;doi:10.7326/M15-2435.