High salt intake ups risk for cataracts

By Dewi Anggraeni

MELBOURNE (JP): In the region, 90 percent of the cases of blindness, including from cataracts, are preventable or curable. Yet, in Indonesia, the country with the third highest incidence of blindness in the world, the World Health Organization estimates there are at least 1.5 million cataract cases.

When asked to theorize why there has been an upward trend in the number of cataract sufferers in Indonesia, Professor Robert Cumming of Sydney University carefully replied: "I don't know much about Indonesia's population. Is the proportion of older people increasing? If that is the case, that might be an obvious answer."

As we become older, it seems, we become more susceptible to cataracts, which eventually lead to blindness.

Old age is not, however, the only reason for the onset of cataracts. Other factors, such as the use of corticosteroid drugs, diabetes, hypertension and smoking, have been known to increase the risk for cataracts.

Since cataracts are a known cause of blindness, medical research is continuing into ways to prevent or at least slow their onset.

And some of the research suggests it is time we looked more closely at our dietary habits. In big cities, where the reliance on junk food is increasing along with the pressures of work and other activities, it is necessary to take time to examine the common ingredients of these foods.

A recent study published in the latest issue of the American Journal of Epidemiology shows a high salt (sodium) intake increases the risk for posterior subcapsular cataracts, the most disabling type of cataract.

Professor Cumming, who took part in the study, told The Jakarta Post his team wanted to study a large population to look at the presence of cataracts, glaucoma and other common eye diseases in the general population, and into those aspects that increased the risk of these diseases. They chose the Blue Mountains, west of Sydney, to conduct their study, which involved 3,654 participants, aged 50 and above, between January 1992 and January 1994.

Following the Wisconsin Cataract Grading System protocol, photographs of each of the participants' eyes were taken to assess the severity of nuclear lens cataracts, and the presence and severity of cortical and posterior subcapsular cataracts.

Participants also were regularly mailed a semiquantitative food frequency questionnaire for them to complete and bring with them to the eye examinations.

"After we collected the data," recounted Cumming, "we became aware of a study in Italy which looked at the relationship between dietary salt intake and cataracts. So we thought we wanted to look at those in a much larger and more comprehensive study."

The study conducted by Cumming's team did not find an association between salt intake and nuclear or cortical cataracts. However, it found that subjects in the highest quintile of salt intake had approximately twice the risk for posterior subcapsular cataract as those in the lowest quintile.

"Our study has several advantages over the Italian study, which was hospital based. Our diagnosis was based on carefully graded lens photographs, not on cataract surgery. All subjects in our study came from the same defined population, and our validated food frequency questionnaire was more complete, based on 145 foods," Cumming said.

When asked to explain the link between excessive salt intake and the increased risk of posterior subcapsular cataracts, Cumming theorized: "Although the interior of the lens is not alive, the outside is very active. There is a transport mechanism that constantly pumps in and out different electrolytes across the membranes of the lens, to keep it transparent, not too soggy and not too dry. It is possible that having a high salt diet might interfere with that mechanism, which leads to reduction in the transparency of the lens. That is what a cataract is."

Cumming also emphasized that people with high blood pressure should watch the amount of salt in their diets. "High blood pressure is a known risk factor for cataracts. Fortunately these people are usually advised by their doctors to reduce their salt intake."

As for the efficacy of antioxidant vitamins in preventing cataracts, Cumming confirmed the efficacy of vitamin A had been proven, while that of vitamin C was still inconclusive.

If we stop and take stock, reducing salt intake should not prove too difficult, especially knowing it can prevent one of the major causes of blindness.