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March 13, 2018

A new study seeks to debunk the 'obesity paradox'

Daily Briefing

    A new study finds that contrary to the so-called "obesity paradox," people with cardiovascular disease who are overweight or obese are not living longer than their normal-weight peers—they're simply getting diagnosed earlier in life.

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    Study details

    The obesity paradox is an observation described in some prior studies that suggests following a diagnosis of cardiovascular disease, people with a higher body mass index (BMI) outlive those who have a normal BMI.

    For the study, published in JAMA Cardiology, researchers sought to test that notion by examining data from 10 studies from the Cardiovascular Disease Lifetime Risk Pooling Project. According to the Los Angeles Times' "Science Now," the studies together assessed 190,672 individuals, none of whom had cardiovascular disease at the start of the studies, and followed them for at least a decade.


    The researchers found that, when compared to those of normal weight (with BMIs between 18.5 and 24.9), overweight men (with a BMI between 25 and 29.9) had a 21% greater risk of developing cardiovascular disease, while overweight women had a 32% greater risk. Meanwhile, obese men (with a BMI between 30 and 39.9) had a 67% greater risk of developing cardiovascular disease, while obese women had an 85% greater risk.

    According to the researchers, the findings largely held across age groups. For instance, among men ages 40 to 59, 37% of those who were overweight had a cardiovascular event over the course of the study, as did 47% of those who were obese and 65.4% of those who were morbidly obese (with a BMI of 40 or above). In comparison, 32% of normal-weight men had a cardiovascular event during the study time frame.

    In addition, the researchers found that individuals at a normal weight were diagnosed with cardiovascular disease later in life and had a longer lifespan overall, compared with those who have higher BMIs. For instance, the researchers found that middle-aged men who were morbidly obese had their first cardiovascular event about 7.5 years before a middle-aged man with a normal weight, while middle-aged women  who were morbidly obese experienced their first cardiovascular event about 7.1 years before a woman with a normal weight. Similarly, when it came to longevity, middle-aged men with a normal weight lived about 5.6 years longer than did middle-aged men who were morbidly obese men, while middle-aged women with a normal weight lived an estimated two years longer than did women who were morbidly obese.


    The researchers wrote that the findings "challenge both the obesity paradox as well as the view that overweight is associated with greater longevity."

    They explained that based on their findings, the obesity paradox is likely caused by individuals with higher BMIs being diagnosed with cardiovascular disease earlier in life, and thus living with the disease longer than their normal weight peers.  In addition, the researchers concluded that "adults who were obese had … a greater proportion of life lived with [cardiovascular disease] morbidity (unhealthy life years), and shorter overall survival compared with adults with normal BMI."

    The researchers added that the "false reassurance" of the obesity paradox "is akin to the phenomenon of lead-time bias observed in other situations, such as with cancer screening. This is especially important because overweight status has been associated with poorer quality of life, functional impairment, and greater work-related disability."

    Sadiya Khan, senior author on the study and an assistant professor of medicine at Northwestern University, added that the study was unique from others on the topic because it "measure[d] how much time is spent in healthy life years rather than just life span." Kahn continued, "Maintaining a healthy BMI is associated with a longer, healthier life, with less risk for cardiovascular disease" (Bakalar, "Well," New York Times, 2/28; Kaplan, "Science Now," Los Angeles Times, 2/28; Monaco, MedPage Today, 2/28).

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