April 07, 2016
Ophthalmology
TAKE-HOME MESSAGE
- In British Caucasian women from the TwinsUK cohort, the authors assessed the relationship between dietary nutrients and progression of nuclear lens changes over 10 years. Findings estimated a genetic influence of nuclear cataract progression at 35% (95% CI, 13–54) compared with environmental factors at 65% (95% CI, 46–87).
- Based on self-reported nutrient intake, vitamin C intake was associated with a 19% reduction in risk of progression of nuclear lens opacification.– Kathleen Freeman, OD, FAAO
Eye Care
This 10-year longitudinal study of over 300 twins showed that, even in a relatively well-nourished group of British women, progression of nuclear lens opacity measured with digital Scheimpflug imaging was a third less in people within the highest tertile of vitamin C dietary intake compared with those in the lowest. While this is unsurprising given the high concentration of ascorbate in the aqueous humor, this is the first study to show reduced progression in a population-based sample. Interestingly, vitamin supplements seemed to confer no benefit. This study adds to the increasing evidence that (other than AMD) most supplement randomized controlled trials fail to find a benefit with antioxidants despite strong epidemiological evidence of their protection against age-related diseases and cancers. It may be that other factors within a healthy diet—in addition to the antioxidants—also confer health benefits, and that a balanced diet confers greater benefit than individual high-dose supplements. The average dietary intake in this group was twice the RDA of 60 mg, and we found no ceiling effect, suggesting that there is no such thing as too much vitamin C for cataract protection; however, the study was not designed to see if there is a toxicity in very high intakes. We also found that genetic factors explained 35% of progression (compared to ~50% of cross-sectional nuclear cataract measures), again previously seen in other studies of aging such as cognitive change. Environmental factors seem to influence change in age-related traits more strongly than genetic factors, suggesting that it is possible to alter the trajectory of change in nuclear cataract and other aging phenotypes.
Abstract
PURPOSE
To determine the heritability of nuclear cataract progression and to explore prospectively the effect of dietary micronutrients on the progression of nuclear cataract.
DESIGN
Prospective cohort study.
PARTICIPANTS
Cross-sectional nuclear cataract and dietary measurements were available for 2054 white female twins from the TwinsUK cohort. Follow-up cataract measurements were available for 324 of the twins (151 monozygotic and 173 dizygotic twins).
METHODS
Nuclear cataract was measured using a quantitative measure of nuclear density obtained from digital Scheimpflug images. Dietary data were available from EPIC food frequency questionnaires. Heritability was modeled using maximum likelihood structural equation twin modeling. Association between nuclear cataract change and micronutrients was investigated using linear and multinomial regression analysis. The mean interval between baseline and follow-up examination was 9.4 years.
MAIN OUTCOME MEASURES
Nuclear cataract progression.
RESULTS
The best-fitting model estimated that the heritability of nuclear cataract progression was 35% (95% confidence interval [CI], 13–54), and individual environmental factors explained the remaining 65% (95% CI, 46–87) of variance. Dietary vitamin C was protective against both nuclear cataract at baseline and nuclear cataract progression (β = −0.0002, P = 0.01 and β = −0.001, P = 0.03, respectively), whereas manganese and intake of micronutrient supplements were protective against nuclear cataract at baseline only (β = −0.009, P = 0.03 and β = −0.03, P = 0.01, respectively).
CONCLUSIONS
Genetic factors explained 35% of the variation in progression of nuclear cataract over a 10-year period. Environmental factors accounted for the remaining variance, and in particular, dietary vitamin C protected against cataract progression assessed approximately 10 years after baseline.
Journal Abstract
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