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Plasma Lutein & Zeaxanthin Tied to Cataract Risk

Oxidative Stress, Carotenoids and Cataract

Cataracts can be defined as clouding of the lens in the eye due to clumping of lens protein and coloration of the lens because of age, smoking, sunlight exposure, use of oral corticosteroids, estrogen replacement therapy, and diabetes. Nuclear cataract is the most common type of cataract among older individuals, especially women.

The inability to sufficiently defend against or repair accumulated damage from a variety of environmental stressors, including photochemical formation of free radicals, can lead to cataract development. Reactive oxygen species, for example, can damage lens proteins and fiber cell membranes.

Lutein and zeaxanthin are the most abundant carotenoids that accumulate in the lens of the eye, where they appear to filter phototoxic blue light and neutralize reactive oxygen species. Many, though not all, longitudinal studies that have looked at dietary intake or plasma levels of Lutein and zeaxanthin and cataract incidence have reported a relationship between these carotenoids and cataract.

In the present investigation, Finnish researchers examined whether plasma concentrations of Lutein and zeaxanthin are related to age-related nuclear cataract in elderly participants of the Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study.

Study Design

The KIHD Study is an ongoing population-based, cohort study designed to investigate risk factors for CVD and other degenerative disease in a sample of middle-aged men and women. Plasma concentrations of carotenoids were determined in 1689 participants (1557 men and 783 women), aged 61-80 years. Nuclear cataract diagnoses were determined by an ophthalmologist using lens photography and grading.

Nuclear cataracts diagnosed were classified into tertiles according to plasma concentrations of Lutein and zeaxanthin. The association of plasma Lutein and zeaxanthin concentrations with age-related nuclear cataract was assessed using the Cox proportional hazards model.

Results

A total of 113 cases of incident age-related cataracts were confirmed, of which 108 cases were nuclear cataracts.

Subjects in the highest tertiles of plasma concentrations of Lutein and zeaxanthin had 42% and 41% lower risks of nuclear cataract, respectively, compared with those in the lowest tertiles. (Relative risk (RR) 0.58, 95% CI 0.35, 0.98; p = 0.041 for Lutein. For zeaxanthin, RR 0.59, 95% CI 0.35, 0.99; p= .0.046).

These associations were observed after adjustment for age, examination year, sex, BMI, smoking, alcohol consumption, serum LDL-cholesterol, serum HDL-cholesterol, years of education, use of oral corticosteroids, history of diabetes and history of hypertension with current use of antihypertensive medication.

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Comment

These results suggest that higher plasma levels of the carotenoids Lutein and zeaxanthin are associated with risk reduction for nuclear cataract in the elderly. According to the authors, “there may be other protective factors of the diet (e.g. synergism of carotenoids with vitamin C or other antioxidants) that may partly explain the observed results”.

The researchers also note that both compounds appear to provide similar levels of protection from cataracts, an observation that challenges the hypothesis that dietary zeaxanthin intake is more important for lens health.

Reference

1. Reference: Karppi J, et al. Plasma lutein and zeaxanthin and the risk of age-related nuclear cataract among the elderly Finnish population. Br J Nutr published ahead of print, 2012.