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A large population study links higher dietary and plasma vitamin C levels to reduced risk of cataract development.
In the recently completed Indian Age-Related Eye Study, vitamin C from food is associated with reduced risk of cataracts. Results of the study are published in the journal Ophthalmology.
Researchers brought their investigation to India based on the notion that India accounts for about 20% of global blindness, largely from cataracts. The researchers state that, even when surgery is taken into account, the Indian population shows greater risk of cataract than western populations.
A total of 5702 adults, age 60 or older, completed the study. Each subject was interviewed for lifestyle factors, provided a blood sample, and conducted an eye examination. Aside from checking vitamin C content in the blood and diet, other antioxidants (e.g., lutein, zeaxanthin, retinol, and tocopherols) were measured.
The researchers observed cataracts in 72.7% of the population and observed an inverse association between vitamin C levels (in plasma and the diet) and evidence of cataract. “Strong inverse associations” were observed even after adjustment for age and sex (men were found to have lower vitamin C levels).
Lifestyle factors associated with low vitamin C levels included increased age, current tobacco use, outdoor exposure, and use of biomass cooking fuel, which can degrade available vitamin C in food.
Previous studies conducted in other countries produced conflicting results, but the authors of this study claim many of those studies were small and low-powered to detect other large effects.
“There is strong biological plausibility for the importance of vitamin C in the lens,” wrote the study’s author. “Vitamin C is found at concentrations in lens or aqueous of approximately 20- to 30-fold that of the plasma and even higher in the vitreous…Vitamin C is a powerful reducing agent and protects the lens from oxidative stress.”
The study supports previous research conducted in Indian populations and, while previous studies in other countries do not always complement these results, many of those studies are believed too be small and low-powered in design.
Only 69 patients reported taking nutritional supplements; thus, the researchers could not state whether or not plasma vitamin C status was influenced by supplementation.
Lutein, zeaxanthin, and retinol also demonstrated inverse associations to cataract development in this study.