About 20 percent of the world’s blind population resides in India, with cataract being the most common reason for blindness. Several factors such as environmental agents, poor nutrition and some genetic factors are responsible for the higher occurrence of cataract in the country. Some small-scale studies have shown that antioxidants retard the development of cataract. Researchers of the present study examined the relationship between cataract and the levels of vitamin C as well as other antioxidants in blood. A strong association was found between low levels of vitamin C and the prevalence of cataract.
The researchers of this study had undertaken a small feasibility study prior to the current study, in which they proved an inverse relationship between the levels of vitamin C in blood, and the occurrence of cataract. Compared to western countries, India and other countries with similar economic growth have a very high prevalence of cataract. Identifying a protective substance such as vitamin C may help in devising strategies to decrease the incidence of cataract in these countries. In the present study, participants were selected from both the northern and southern parts of India, to have an adequate representation of India as a whole.
* A total of 7,518 individuals aged more than 60 years were selected for the study, of whom, 5,638 completed the study.
* Data regarding the socioeconomic status, tobacco and alcohol consumption, diet, and fuels used for cooking was collected through interviews. Body mass index was measured to assess the nutritional status.
* Vitamin C consumption was measured by recording 24-hour diet consumption and then measuring vitamin C in each food item by using the “Indian Council of Medical Research Food Composition Tables”. Later, blood samples were collected to measure the levels of vitamin C and other antioxidants.
* The degree and type of cataract was assessed by using the Topcon SL-D7 digital photo slit lamp.
* Levels of vitamin C were lower in people with low socioeconomic and nutritional status, and in those who smoked tobacco and used biomass as cooking fuel.
* A strong inverse relation was observed between increasing levels of plasma vitamin C and cataract of any type.
* A weak inverse association was found with other antioxidants such as retinol, beta carotene, a tocopherol, zeaxanthin and lutein.
* Higher incidence of cataract was observed in those who consumed less vitamin C.
In the present study, levels of vitamin C in blood were measured simultaneously with the assessment of cataract. Hence, researchers could not establish the temporal relationship between cataract and the deficiency of vitamin C. Follow up measurements are necessary to prove this causative association. Moreover, in the present study, only a single measurement of vitamin C consumption was taken. This could have led to an error in establishing the association between vitamin C and cataract.
Cataract is known to occur because of oxidative damage to the lens present within the eye. Vitamin C is a powerful antioxidant and its concentration in the lens is 20 to 30 times higher than that in the blood. Levels of vitamin C are higher even in the fluid in which the lens is placed. Hence, due to a fall in the levels of vitamin C in blood, the concentration of vitamin C reduces in the lens as well, resulting in cataract. The authors conclude, “The strong association with vitamin C and cataract in our vitamin C depleted population may, in part, explain the high levels of cataract in India.”
For More Information:
Inverse Association of Vitamin C with Cataract in Older People in India
Publication Journal: Ophthalmology, 2011
By Ravilla D. Ravindran; Praveen Vashist; Aravind Eye Hospital, Pondicherry, India and All India Institute of Medical Sciences, New Delhi, India