Diabetes mellitus is a significant global health challenge, with prevalence increasing rapidly. In 2021, the International Diabetes Federation estimated that 537 million adults worldwide were living with diabetes, a figure projected to reach 783 million by 2045 [1]. Visual impairment (VI) is considered one of the most severe complications of diabetes, and patients with diabetes face a 25-fold higher risk of blindness compared with non-diabetic individuals [2]. Diabetic retinopathy is the most recognized cause of VI, but growing evidence suggests that metabolic changes related to diabetes also contribute to a wider range of ocular and systemic conditions affecting vision [3]. Identifying modifiable risk factors associated with VI is essential to prevention and early intervention.

Anthropometric measures such as body weight, body mass index (BMI), and waist circumference are widely recognized markers of metabolic health. Improvements in obesity-related indices have been shown to lower blood pressure, enhance insulin sensitivity, and reduce proteinuria [4,5]. However, longitudinal studies reveal that fluctuations in body weight and related measures are common, and such instability—reflecting metabolic dysregulation—may independently increase the risk of both macrovascular and microvascular complications [6,7]. Since these complications can contribute to VI, it is important to understand their implications.

To address this question, we investigated the association between changes in anthropometric measurements and risk of VI in patients newly diagnosed with type 2 diabetes mellitus (T2DM), using a nationwide cohort in Korea. From more than 21 million individuals aged 40 years or older who underwent health screening between 2010 and 2015, a total of 371,455 patients with newly diagnosed T2DM (mean age 56.2±9.3 years, 61.0% male) was included after applying a 2-year washout period. Patients lacking follow-up screening, with missing variables, or with prior VI were excluded. T2DM was defined by International Classification of Diseases, 10th Revision (ICD-10) codes with prescriptions for antidiabetic medications or fasting plasma glucose ≥126 mg/dL. Participants were categorized into seven groups of anthropometric change over a 4-year interval following the initial diabetes diagnosis: large decrease (≥15%), moderate decrease (≥10% and <15%), mild decrease (≥5% and <10%), stable (change <5%), mild increase (≥5% and <10%), moderate increase (≥10% and <15%), and large increase (≥15%).

The study outcome was new-onset VI, defined by ICD-10 codes indicating VI or blindness, corrected visual acuity <6/60, or official registration in the national disability registry. Patients were followed until VI, death, or December 2022. Covariates were demographic characteristics, lifestyle behaviors (smoking status, alcohol consumption, and regular exercise), comorbidities (hypertension, dyslipidemia, heart failure, ischemic stroke, and chronic kidney disease), and socioeconomic status. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for VI across anthropometric change categories, with the stable group as reference.

During a mean follow-up of 6.0 years, 3,864 cases of VI occurred, yielding an incidence rate of 1.73 per 1,000 person-years. Across body weight, BMI, and waist circumference, the stable groups consistently showed the lowest risk. Both increases and decreases in each anthropometric measure were associated with higher incidence of VI, with a graded trend such that larger changes corresponded to greater risk (Table 1).

After adjusting for all covariates, HRs for VI followed a U-shaped pattern across all three measures, with the greatest risks observed among those with changes exceeding 15%. Patients with a body weight increase ≥15% had an HR of 1.94 (95% CI, 1.50 to 2.51), those with a BMI increase ≥15% had an HR of 1.80 (95% CI, 1.40 to 2.32), and those with a waist circumference increase ≥15% had an HR of 1.45 (95% CI, 1.20 to 1.75), relative to the stable group. Importantly, not only large increases but also large decreases in body weight, BMI, or waist circumference were linked to higher VI risk, highlighting the detrimental impact of anthropometric instability regardless of direction.

These findings suggest that fluctuations in anthropometric measures, whether upward or downward, are associated with metabolic dysregulation and ocular complications in diabetes. VI in patients with diabetes can result from multiple pathologies, including diabetic retinopathy, macular edema, cataracts, glaucoma, and ischemic optic neuropathy [3]. Chronic hyperglycemia-induced microvascular injury remains the main mechanism, but obesity further exacerbates systemic inflammation, endothelial dysfunction, oxidative stress, and insulin resistance, all of which may contribute to vision-threatening diseases [8]. Conversely, unintentional weight loss may signal frailty or underlying illness, which can also predispose to complications. The observed U-shaped relationship underscores that both extremes—significant weight gain and loss—carry elevated risk.

Recent studies have shown that variability in body weight or BMI is associated with greater morbidity and mortality from cardiovascular diseases [6,9]. For microvascular complications, increased BMI has been linked to retinal vessel changes, and variability in waist circumference or BMI to higher risks of neuropathy and nephropathy [7,10]. Although the mechanisms remain unclear, we hypothesize that systemic metabolic dysregulation may exacerbate both microvascular and macrovascular complications, elevating the risk of VI.

The strengths of this study include its large, population-based cohort; extensive follow-up; and availability of repeated anthropometric measures, enabling evaluation of the association between changes in body weight, BMI, and waist circumference and the relatively rare outcome of VI. However, several limitations should be considered. First, changes in anthropometric measures were assessed within a defined timeframe, without accounting for subsequent changes during follow-up. Second, the National Health Insurance Service (NHIS) dataset lacked detailed clinical information such as glycated hemoglobin levels, which would allow better assessment of diabetes severity. Third, BMI and waist circumference have inherent limitations as surrogate measures of adiposity, as they cannot distinguish fat from muscle mass.

In conclusion, this large population-based cohort study demonstrated that anthropometric changes are independently associated with higher risk of VI in patients newly diagnosed with T2DM. A graded relationship was evident, with more pronounced anthropometric changes correlating with higher HRs of VI, as observed not only in groups with increasing body weight, BMI, and waist circumference but also in groups with significant reductions in these measures. Further research is necessary to elucidate the mechanisms linking anthropometric changes to VI.

This study protocol was approved by the Institutional Review Board of Seoul National University Hospital (IRB No. 2206-061-1331), Seoul, Korea. Informed consent was not required, as the analysis utilized deidentified and anonymized data.