Cataractogenesis occurs as a result of ageing, smoking, exposure to UV radiation and genetic predisposition. Antioxidants can reduce the cataract risk as found in animal models and humans and vitamin D is one of them. This epidemiological study based in South Korea looked at cataract formation and serum vitamin D levels. Study data was obtained from Korean National Health and Nutrition Examination Survey. Exclusion criteria were aged 39 years or younger, no serum Vitamin D levels measured and no slit-lamp examination. Cataracts were graded according to the internationally well-established Lens Opacities Classification Systems III (LOCS III) for assessment. Cataracts were graded as cortical, nuclear, anterior subcapsular, posterior subcapsular, or mixed type. Age-related cataracts were defined as one or more types. Vitamin D levels in the serum were collected after eight hours of fasting and measured with radioimmunoassay. Sunlight exposure was categorised above or below five hours per day. Systemic medical history was also considered. They found that in 9479 men significantly lower cataract prevalence (24% lower) was associated with higher levels (highest quintile) of serum vitamin D compared to the lowest levels of serum vitamin D (lowest quintile), after adjustment for potentially confounding factors. Biologically this is explained by vitamin D inhibiting oxidation of proteins in the lens that is a key step in cataractogenesis. This study doesn’t look at associated intraocular, i.e. aqueous humour levels of vitamin D and see whether that correlates with serum levels. It only hypothesises why vitamin D levels are lower in women e.g. because fewer hours are spent exposed to daylight sun required by the skin to produce vitamin D. Does the cataract protective effect of vitamin D outweigh the cataractogenic effect of UV light exposure? There is no genetic analysis on vitamin D receptor gene known to have frequent polymorphisms. This is yet another study suggesting that increasing intake of dietary supplements may prevent cataract formation.
Association between serum 25-hydroxyvitamin D levels and age-related cataracts
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