Should Korea's obesity threshold be raised to BMI of 27 or higher?

A new study suggests that the obesity threshold for Koreans should be raised to a body mass index (BMI) of 27 or higher.

The Health Insurance Research Institute under the National Health Insurance Service (NHIS) said Monday that it presented the findings at the “2024 Autumn Conference of the Korean Society for Health Education and Promotion" last Friday.

The institute followed up on 8.47 million adults who underwent general health checkups in 2002 and 2003 for 21 years and analyzed the risk of death and cardiovascular disease by BMI.

The analysis's results showed a U-shaped association between BMI and all-cause mortality, with the lowest risk of death in the 25th percentile of BMI, which is the current definition of obesity.

After excluding deaths within five years of the baseline, the analysis showed that the risk of death was lowest in the 25th percentile, while it was 1.72 times and 1.64 times higher in the 18.5th percentile or below and 35th percentile or higher than in the 25th percentile, respectively.

The study looked specifically at the increased risk of mortality in BMI 25 and above and found that the increased risk was twice as great in BMI 29 compared to the previous bands.

Analyzing the association between BMI and cardiovascular events found that the overall risk of disease increased with increasing BMI, so there is no clear evidence to identify BMI 25 as an obesity cutoff.

The cardiovascular and cerebrovascular disease risk was lowest at a BMI below 18.5. It increased across the board, with the highest risk of hypertension and diabetes at a BMI of 34, dyslipidemia at a BMI of 33, and cardiovascular and cerebrovascular disease at a BMI of 34.

Regarding the increased risk of disease at BMI 25 and above, hypertension, diabetes, and dyslipidemia increased at BMI 27, cardiovascular disease at BMI 29, and cerebrovascular disease at BMI 31 compared to the previous bands.

“Twenty years ago, the analysis showed the lowest risk of death at a BMI of 23, and since our body shape, lifestyle, and disease patterns have changed to resemble those of the West, the lowest risk of death is now at a BMI of 25,” said Professor Oh Sang-woo of Dongguk University Ilsan Hospital.

“The association between obesity and disease is similar to what it has been in the past. The diagnostic criteria for obesity should be set by prioritizing the association with disease and considering mortality data as a secondary consideration,” Professor Oh said. “Based on these findings, we believe that raising the current BMI to 27 is an appropriate diagnostic criterion for Koreans.”

Lee Sun-mi, director of the institute’s Health Management Research Center, said, “This study is the largest health insurance big data-based follow-up study on obesity criteria. Considering the risk of cardiovascular disease and death in Korean adults, the current obesity criteria should be raised to a minimum BMI of 27 or higher. China already applies a BMI of 28 or higher as obesity criteria.”

The NHIS also said. “We will continue to promote healthcare projects centered on the obese population who are at high risk of chronic diseases and death.