Obesity Paradox Deflated by New Study Data

MARCH 01, 2018
Matt Hoffman
Sadiya Khan, MD, MSc
Despite prior evidence alluding to a lower all-cause mortality in overweight individuals compared to those who are not, new data has shed light on this somewhat perplexing obesity paradox.

The study determined that the obesity paradox appears to be principally caused by an earlier diagnosis of cardiovascular disease (CVD)—thus resulting in a greater proportion of life with CVD morbidity.

Led by Sadiya Khan, MD, MSc, a cardiologist with Northwestern Medicine and an assistant professor of medicine at Northwestern University Feinberg School of Medicine, the study revealed that despite having similar longevity compared to those with normal body mass index (BMI), those who are overweight have a significantly higher risk of both cardiovascular morbidity and mortality. They also had a heightened risk of developing CVD at an earlier age.

"The obesity paradox caused a lot of confusion and potential damage because we know there are cardiovascular and non-cardiovascular risks associated with obesity,” Khan said in a statement. “I get a lot of patients who ask, 'Why do I need to lose weight if research says I'm going to live longer?' I tell them losing weight doesn't just reduce the risk of developing heart disease, but other diseases like cancer. Our data show you will live longer and healthier at a normal weight."

The population-based study examined individual data from 1964 to 2015, including 10 US prospective cohorts that consisted of 3.2 million person-years of follow-up. There were 190,672 in-person examinations included in the investigation, with the mean patient age of 46.0 years (standard deviation [SD], 15.0) for men and 58.7 years (SD, 12.9) for women (n = 140,835; 73.9%).

The hazard ratios for CVD incidence for those aged 40 to 59 years were as follows:
  • Overweight: 1.21 (95% CI, 1.14-1.28) for men, and 1.32 (95% CI, 1.24-1.40) for women.
  • Obesity: 1.67 (95% CI, 1.55-1.79) for men, and 1.85 (95% CI, 1.72-1.99) for women.
  • Morbid Obesity: 3.14 (95% CI, 2.48-3.97) for men, and 2.53 (95% CI, 2.20-2.91) for women. 
Normal weight male individuals were expected to live roughly the same amount of years as overweight men, 1.9 years longer than their obese counterparts, and 6 years longer than those who were morbidly obese. Women with normal weight had 1.4 years longer life expectancy compared to those who were overweight, 3.4 years longer than obese women, and 6 years longer than morbidly obese women.

"A healthy weight promotes healthy longevity or longer health span in addition to lifespan so that greater years lived are also healthier years lived," Khan said. "It's about having a much better quality of life."

The lifetime risk of incident CVD events for middle-aged men were 13.72 per 1000 person-years for those with normal BMI, compared to 15.53, 20.21, and 30.15 for those in the overweight, obese, and morbidly obese categories, respectively. There were 7136 cases of fatal or nonfatal myocardial infarction, 3733 cases of fatal or nonfatal stroke, and 4614 cases of congestive heart failure.

The study’s limitations included the use of BMI at index ages without accounting for BMI changes across follow-up, as well as the lack of universal data being available on central adiposity.

Current estimates indicate that the prevalence of obesity is 35% for men and 41% for women in the United States.

The study, “Association of Body Mass Index With Lifetime Risk of Cardiovascular Disease and Compression of Morbidity,” was published in JAMA Cardiology.

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