Vitamin D Supplementation and the Incidence of Cataract Surgery in Older Australian Adults

Observational studies suggest that higher serum 25-hydroxyvitamin D concentration may be associated with lower risk of cataract. However, no randomized controlled trials (RCTs) have assessed the effect of vitamin D supplementation on the incidence of cataract. We aimed to assess whether vitamin D supplementation reduces the incidence of cataract surgery.We conducted an ancillary study of D-Health Trial, a randomized, double-masked, placebo-controlled trial of monthly vitamin D for the prevention of all-cause mortality conducted from 2014 to 2020 within the Australian general population.We invited 421,207 men and women aged 60-84 years to participate; including an additional 1,896 volunteers, 40,824 expressed interest. Those with hypercalcemia, hyperparathyroidism, kidney stones, osteomalacia or sarcoidosis, or who were taking500 international units (IU) supplemental vitamin D per day were excluded. 21,315 people were randomized. 1,390 participants did not fulfil the eligibility criteria for this analysis (linked data available, no cataract within first 6 months) leaving 19,925 included. The median follow-up was 5 years. .60,000 IU of vitamin DThe primary outcome for this analysis was the first surgical treatment for cataract, ascertained through linkage to universal health insurance records and hospital data.Among 19,925 participants eligible for the analysis of incident cataract (mean age 69.3 years, 46% women) 3,668 (18.4%) underwent cataract surgery during follow-up (n=1,841 (18.5%) of the vitamin D group and n=1,827 (18.3%) of the placebo group). The incidence of cataract surgery was similar between the two groups (incidence rate 41.6 and 41.1 per 1,000 person-years in the vitamin D and placebo groups, respectively; hazard ratio 1.02; 95% CI 0.95 to 1.09). In pre-specified subgroup analyses, the effect of vitamin D supplementation on the incidence of cataract surgery was not modified by age, sex, body mass index, predicted serum 25-hydroxyvitamin D concentration, or ambient ultraviolet radiation.Routinely supplementing older adults who live in an area with a low prevalence of vitamin D deficiency with high-dose vitamin D is unlikely to reduce the need for cataract surgery.