Nutritional intake, environmental factors, and their impact on myopia prevalence in Korean children aged 5–12 years

**Background:** Myopia is a complex condition influenced by genetic, environmental, and lifestyle factors. While dietary factors may affect myopia development, the relationship is not fully understood. This study aimed to investigate the association between daily dietary nutrient intake and myopia in Korean children aged 5–12 years using data from the seventh Korea National Health and Nutrition Examination Survey (KNHANES VII).

**Methods:** Data were obtained from KNHANES VII, a cross-sectional population-based survey conducted in 2016. Of 519,169 participants, 24,345 children aged 5–12 years were included after exclusions (missing refractive error data, energy intake <500 or >5000 kcal/day, history of ophthalmic surgery, missing general characteristics). Refractive error was measured using an auto-refractor keratometer without cycloplegia; myopia was defined as spherical equivalent (SE) ≤ -0.50 D, high myopia as SE ≤ -6.00 D, hyperopia as SE ≥ +0.75 D, and emmetropia as -0.50 D < SE < +0.75 D. Dietary intake was assessed via 24-hour recall, and 24 nutrients were analyzed. Statistical analyses included chi-square tests, analysis of covariance, univariate and multiple logistic regression (adjusted for age, sex, BMI, parental myopia, near-work hours), and Bonferroni correction for multiple comparisons.

**Key Results:** The study included 24,345 children (51.84% male, 48.16% female). Mean SE was -2.37 D (SD 1.55) in myopic children (61.38%), +0.01 D (SD 0.29) in emmetropic (32.00%), and +1.84 D (SD 1.04) in hyperopic (6.62%). Myopia prevalence increased with age: 30.50% at ages 5–6, 47.43% at 7–8, 67.39% at 9–10, and 78.76% at 11–12. High myopia prevalence was 0% at ages 5–8, 0.81% at 9–10, and 4.46% at 11–12. In adjusted logistic regression, the risk of myopia was highest in children aged 11–12 (OR 11.54, 95% CI 10.39–12.82, p<0.0001). Having both parents with myopia increased risk 2.04-fold (95% CI 1.89–2.20, p<0.0001). Urban residence was associated with a 1.09-fold increased risk (95% CI 1.02–1.15, p=0.0066).

Dietary analysis showed that children with myopia had significantly lower average daily intake of fat (51.05 g vs. 55.47 g in emmetropia), omega-3 fatty acids (1.30 g vs. 1.37 g), and retinol (144.97 μg vs. 149.82 μg) but higher intake of most other nutrients compared to emmetropic children. High intake of carbohydrates (adjusted OR 1.32, 95% CI 1.24–1.40), protein (OR 1.57, 95% CI 1.48–1.67), phosphorus (OR 1.67, 95% CI 1.57–1.77), iron (OR 1.56, 95% CI 1.47–1.66), potassium (OR 1.65, 95% CI 1.56–1.75), and sodium (OR 2.06, 95% CI 1.95–2.19) were associated with increased myopia risk. High vitamin C intake was associated with a 1.85-fold increased risk (95% CI 1.75–1.97). Nutrient Adequacy Ratio (NAR) and Mean Adequacy Ratio (MAR) were generally higher in myopic children, except for fiber, calcium, potassium, and vitamins A and C.

**Clinical Implications:** This large population-based study highlights that dietary factors, particularly high intake of carbohydrates, protein, phosphorus, iron, potassium, and sodium, are associated with increased myopia risk in Korean children. High sodium intake showed the strongest association (2.05-fold increased risk). These findings suggest that dietary modifications, such as reducing sodium and refined carbohydrate intake, may be considered in myopia prevention strategies. However, the cross-sectional design precludes causal inference, and the lack of cycloplegic refraction may overestimate myopia prevalence. Future longitudinal studies and randomized controlled trials are needed to confirm these associations and explore underlying mechanisms. The results underscore the importance of considering diet alongside environmental factors (e.g., near-work, outdoor time) in childhood myopia management.