Many epidemiological studies have demonstrated that body mass index (BMI) is associated with the risk of developing age-related cataracts. These reports have suggested that high and low BMIs can affect the onset or progression of age-related visual impairment. However, few prospective studies have examined this relationship in a general Asian population. Therefore, in this study, we investigated whether BMI was associated with an increased risk of age-related cataracts by performing a 5-year prospective population-based study in a middle-aged Japanese population.

This 5-year population-based study included 35,365 men and 40,825 women (aged 45–74 years), who were recruited into the Japan Public Health Center (JPHC)-based Prospective Study and had not reported cataracts in a baseline survey. The self-reported diagnosis of age-related cataracts was used in the analysis of this study.

At follow up, 1,004 men (2.84%) and 1,807 women (4.43%) reported new diagnoses of age-related cataracts. The multivariate odds ratios ( ORs ) for those in the lowest and the highest BMI categories, compared with a BMI category of 21.0–22.9 as a reference point (OR, 1.00), were 1.29 [95% confidence interval (CI) 0.93–1.79] and 1.15 (95% CI 0.96–1.39) in men, and 1.23 (95% CI 0.97–1.55) and 1.19 (95% CI 1.04–1.36) in women.

Previous studies have suggested high BMI as a risk factor of age-related cataracts for Caucasian populations in developed countries while low BMI for populations living in developing countries. In contrast to those studies, the present large-cohort study showed a U-shaped association between BMI and the incidence of cataracts in Japanese men and women.