Severe obesity with fewer comorbidities is more prevalent in older Japanese women than in older Japanese men: Novel findings from the K7Ps Study-9
The K7Ps Study-9 reveals that severe obesity accompanied by fewer comorbidities is more common among older Japanese women than among older Japanese men.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine the human body as a complex, high-performance vehicle. Sometimes, due to diet, genetics, or lifestyle, this vehicle carries extra cargo—what scientists call "obesity." When that cargo gets really heavy, it's like trying to drive a truck loaded with boulders; it puts immense strain on the engine and the frame, leading to breakdowns like heart trouble or diabetes. These breakdowns are called "comorbidities." Usually, when we think about who carries the most weight, we might guess it's the men, but in many parts of the world, women actually carry more of this extra cargo. However, there's a twist: women often seem to keep their engines running longer than men, living to older ages. Japan is the ultimate champion of this "longevity" game, especially for women. But here's the mystery: in Japan, men usually carry more weight than women. So, does this rule hold true when they get very old? And if older Japanese women do start carrying more weight, does their "engine" (their health) suffer just as much as the men's, or is there something different happening? This is the question researchers set out to solve.
The scientists behind this study, led by Kei Nakajima and Airi Sekine from Japan Women's University, decided to dig into a massive digital treasure chest of health records called the National Database of Health Insurance Claims. They looked at over 8.9 million adults aged 40 to 74 living in the Kanto region (which includes Tokyo and six surrounding prefectures) who had taken government-mandated health checkups between 2018 and 2019. They were specifically hunting for "severe obesity," which they defined as having a Body Mass Index (BMI) of 35.0 kg/m² or higher, and the most extreme "Class 3" obesity, which is a BMI of 40.0 kg/m² or higher. They also carefully filtered out people with specific medical conditions or medications that could artificially inflate weight, ensuring they were looking at the real picture.
Here is the surprising twist the study uncovered: while men in Japan generally carry more weight than women across most age groups, the story flips completely once people hit their 60s and 70s. In the 70–74 age group, the "weight burden" was actually heavier for women. About 2.87% of women in this age bracket were severely obese, compared to only 2.26% of men. When looking at the entire group of people aged 60 and older, women were more likely to be severely obese (0.33% to 0.60%) than men (0.16% to 0.51%).
But the real magic isn't just about who carries the weight; it's about how that weight affects the vehicle's engine. The researchers checked the health "dashboard" of these severely obese individuals, looking at things like waist size, blood pressure, cholesterol, and whether they were taking medication for high blood pressure, diabetes, or heart disease. They found that even though older Japanese women were carrying more of this severe weight, their engines were surprisingly less strained than the men's. Men with severe obesity had significantly higher rates of high blood pressure, diabetes, and heart disease, and they were much more likely to be taking medication for these issues. For example, in the 70–74 age group, 84.4% of men with severe obesity were on blood pressure medication, compared to 81.9% of women, and 39% of men were on diabetes medication versus 27.6% of women.
The authors suggest that this points to a unique phenomenon: severe obesity with fewer comorbidities (fewer engine breakdowns) is more common in older Japanese women than in older Japanese men. It's as if these women are driving a truck loaded with heavy boulders, yet their engine is humming along with fewer sputters and breakdowns than the men driving lighter trucks. The study notes that this might help explain why Japanese women have the longest life expectancy in the world, even if they become heavier in their later years. However, the researchers are careful to say this is an observation based on data up to age 74; they didn't have data for people 75 and older, who might face different health challenges. So, while the data suggests a fascinating pattern of "heavy but healthy" aging for women in Japan, it's a clue rather than a final, solved mystery for the entire population.
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