Maintaining optimal body weight is crucial for preventing disease and maintaining quality of life. Obesity is strongly linked to chronic diseases like metabolic syndrome, type 2 diabetes, hypertension, and cardiovascular disease, leading to higher morbidity and mortality. Conversely, underweight is associated with increased all-cause mortality and conditions such as osteoporosis, sarcopenia, and anemia. Obesity prevalence has increased rapidly worldwide, including South Korea, particularly among men. However, underweight and malnutrition remain prevalent in vulnerable populations, such as people with disabilities, even in high-income countries. Previous studies have often focused on specific disability types or used self-reported weight data. South Korea's universal health insurance and national disability registration system, linking disability type and severity to health data, provides a unique opportunity to study this comprehensively. This study examined 10-year trends (2008-2017) in weight and prevalence of underweight, overweight, and obesity among people with disabilities, considering disability severity and type.

Existing research primarily focused on individuals with specific disabilities (intellectual, physical, spinal cord injury) or relied on self-reported data. Studies on the weight distribution across the entire disabled population and long-term trends were limited. While the rising global obesity epidemic is well-documented, the prevalence of underweight in high-income countries, particularly among vulnerable groups, is often overlooked. Existing literature highlights the increased risk of obesity among individuals with intellectual disabilities due to factors like limited control over food intake and physical activity, medication side effects, and potentially the quality of care they receive. For individuals with physical disabilities, physical inactivity and muscle atrophy are contributing factors to higher obesity rates. Conversely, certain disability types (musculoskeletal, respiratory) have been linked to increased underweight prevalence. This study aimed to fill the research gap by providing a comprehensive analysis of weight trends across all disability types and severities in South Korea.

This serial cross-sectional analysis utilized linked data from South Korea's national disability registration and national general health checkup databases (2008-2017). Over 10 million subjects per year were included. Body Mass Index (BMI) was calculated, and underweight (<18.5 kg/m²), overweight (≥23.0 kg/m²), obesity (≥25.0 kg/m²), and severe obesity (≥30.0 kg/m²) were defined using WHO Asia-Pacific regional guidelines. Disability type and severity were categorized according to the national registration system. Other variables collected included age, sex, income (proxied by insurance premiums), residential area, comorbidities (Charlson comorbidity index), smoking, alcohol consumption, and physical activity. Descriptive statistics and age-standardized prevalence rates were calculated. Multinomial logistic regression analyzed the odds of underweight, overweight, obesity, and severe obesity, adjusting for socio-demographic and clinical variables (2017 data). The age structure of the 2005 Korean population census was used for age standardization. Data analysis was performed using SAS software, with two-sided p-values < 0.05 considered significant. Ethical approval was obtained from the International Review Board of Chungbuk National University.

Over 10 million subjects participated in the general health checkup annually from 2008 to 2017. In 2017, the analysis included 14,246,785 individuals aged 19-110. Age-standardized obesity and severe obesity prevalence significantly increased over the 10 years in all groups. However, age-standardized underweight prevalence decreased among those without disabilities, while it increased in 2012 and remained steady in those with disabilities. In 2017, people with disabilities had higher odds of underweight (OR 1.41 for males, 1.31 for females) compared to those without, especially those with severe disabilities (OR 2.00 for males, 1.83 for females). Women with disabilities had higher odds of obesity than women without disabilities regardless of severity (OR 1.40). Mental disorders showed the highest obesity prevalence, followed by epilepsy and developmental disabilities. BMI and waist circumference increased significantly over time in all groups, with those with disabilities consistently having higher values. Underweight prevalence was significantly higher in males with severe disabilities than those with mild disabilities, while in females, high underweight rates were observed irrespective of severity. Multinomial logistic regression confirmed increased odds of underweight among people with disabilities and different patterns for obesity depending on sex and disability type. Women with severe disabilities, particularly those with mental or developmental disabilities, had the highest odds of severe obesity.

The findings highlight a dual challenge of both obesity and underweight among people with disabilities in South Korea. The increase in underweight prevalence in 2012 among people with disabilities might be attributed to the implementation of a national personal assistance service that year, potentially leading to improved access to health screenings. The higher prevalence of underweight among individuals with severe disabilities could be due to malnutrition and sarcopenia from physical inactivity. The higher obesity prevalence in women with disabilities is likely complex, involving societal pressures, health care access and quality, and potentially overlapping social identities. The study's results align with previous research showing elevated obesity risk among individuals with intellectual disabilities, while also adding important detail on underweight prevalence in this group and the influence of other disability types. The intersection of gender and disability severity significantly influences the prevalence of both underweight and obesity, indicating a need for targeted interventions.

This large-scale study reveals a concerning trend of increasing obesity, along with persistent underweight, among people with disabilities in South Korea. Women with severe disabilities and those with mental or developmental conditions are particularly vulnerable to both extremes of weight. Future research needs to focus on targeted interventions to address the specific needs of different disability groups, considering factors like nutritional support, physical activity promotion, access to healthcare, and medication management. Simultaneous efforts to combat both underweight and obesity are crucial to improving the health and well-being of this population.

The study's reliance on health screening participants might exclude individuals with severe disabilities or limited access to healthcare, potentially biasing the results. The lack of detailed clinical data (e.g., energy intake, disability onset) limits the causal interpretations of the findings. Inaccuracies in anthropometric measurements for individuals unable to stand could also affect the results. The use of insurance premium as a proxy for income might not accurately reflect the socioeconomic status of all participants.