More studies support link between nutrition, cataract

Strongest association with long-term use of vitamin supplements.

Two recently published studies from different continents further support an association between nutrients and cataract formation in older people. Both the Blue Mountains Eye Study in Australia and the Beaver Dam Eye Study in Wisconsin underscore the fact that the lens nucleus is sensitive to nutrient deficiencies.

“As a scientist, I am struck by the consistency of reports of lower risk for cataract among people who use vitamin supplements,” said Julie A. Mares-Perlman, PhD, an associate professor of ophthalmology at the University of Wisconsin in Madison. “When physicians encounter patients with extremely poor diets, a multivitamin supplement might help prevent cataract,” she said. “We certainly do not have conclusive evidence that multivitamins are protective and getting the nutrients we need from foods is preferable. However, taking multivitamins won’t hurt and might help.”

Dr. Mares-Perlman, together with colleague Ronald Klein, MD, professor of ophthalmology and others, conducted a National Eye Institute-funded study that assessed the relationship of nutrition to the 5-year incidence of cataract in participants in the Beaver Dam Eye Study. Of the 3,684 residents in both baseline and follow-up examinations, 3,089 were eligible for analysis of cataract incidence in the present study.

The investigators found that the 5-year risk for any cataract was 60% lower among persons who, at follow-up, reported using multivitamins or any supplement containing vitamin C or E for more than 10 years, compared to nonusers. But while multivitamin use for this lengthy duration significantly lowered the risk for nuclear and cortical cataracts, no association was found for posterior subcapsular cataracts. “We had very few cases of posterior subcapsular cataract, so our ability to detect if there was a protective effect for this type of cataract was extremely low,” Dr. Mares-Perlman told Ocular Surgery News.

Strongest trends

The strongest trend for decreasing risk with increased duration was observed for cortical cataract (adjusted odds ratio 0.9 for 5 years or less of multinutrient use, 0.6 for 6 to 10 years, and 0.4 for more than 10 years). “We were surprised by this finding because our previous work at baseline showed a higher prevalence of cortical cataract in the population that used supplements. This discrepancy could be attributed to a greater likelihood of people who start to take supplements after they learn of having cortical cataracts or related conditions,” said Dr. Mares-Perlman.

The next strongest trend for decreasing risk with increased duration was for nuclear cataract (adjusted odds ratio 0.9 for 5 years or less, 1.1 for 6 to 10 years, and 0.6 for more than 10 years). But posterior subcapsular cataract failed to show a meaningful association with vitamin supplement use (odds ratio 1.2, 1.3 and 0.9, respectively).

The study, which appeared in Archives of Ophthalmology, also looked at supplements separately, specifically vitamins E and C. “Overall cataract risk was lower in people taking vitamin E and C supplements, but most of these people also took multivitamins. The number of people who took vitamin E exclusively or just took vitamin C was very low,” said Dr. Mares-Perlman.

Independent influence

Vitamin users are more likely to engage in other healthy behaviors that might retard cataract development. Still, there is some evidence for an independent influence of supplements, said Dr. Mares-Perlman. Although the investigators assessed lifestyle (active versus sedentary), alcohol use, smoking history, body mass index and daily dietary intake, “I think we always worry about what we are not measuring,” she said. “For example, maybe stress and the steroid hormones it produces could be related but these things have not been studied.” Multinutrient users were more likely to be female, have a physically active lifestyle and a lower body mass index. “We know in general that women are more likely to use supplements than men,” Dr. Mares-Perlman said.

To assess the possibility that recall bias may have influenced the results, “we took advantage of the total population that was evaluated in the Beaver Dam Eye Study in this particular subanalysis. At baseline, about half of those people were asked detailed information about supplement use. They were part of a nutritional study,” said Dr. Mares-Perlman.

The authors evaluated the incidence of cataract in 249 long-term multivitamin supplement users versus 984 nonusers by diet characteristics in a subsample of the nutrition study participants. “More-nutrient dense diets among supplements users are not likely to explain the association,” Dr. Mares-Perlman said.

Study down under

A more specific link between nutrients and cataract formation in older people was found in the cross-sectional phase of the Blue Mountains Eye Study, consisting of 2,900 people (ages 49 to 97) living in an urban community near Sydney, Australia. Higher intakes of protein, vitamin A, niacin, thiamin and riboflavin were associated with reduced prevalence of nuclear cataract. Similarly, intake of polyunsaturated fats was associated with reduced prevalence of cortical cataract. Like the Beaver Dam Eye Study, no nutritional benefits for posterior subcapsular cataract were found.

The Australian diet and cataract study appeared in Ophthalmology and was headed by Robert G. Cumming, PhD, of the Department of Public Health and Community Medicine at the University of Sydney.

“Our study provides some support for the antioxidant theory of cataractogenesis, as two nutrients with antioxidant potential (vitamin A and riboflavin) were associated with reduced prevalence of nuclear cataract,” stated the authors. “Perhaps our most important finding is that niacin and riboflavin may protect against nuclear cataract. This is consistent with two other observational epidemiologic studies and one randomized controlled trial.”

Macronutrient impact

Regarding macronutrients, the Blue Mountains Eye Study found that total energy was not associated with any of the three types of cataracts. However, higher intakes of polyunsaturated fats were statistically significantly associated with a lower prevalence of cortical cataract, and higher intakes of fiber and protein were statistically significantly associated with a lower prevalence of nuclear cataract. In contrast, higher total fat intakes were statistically significantly associated with a higher prevalence of posterior subcapsular cataract.

Various micronutrients (calcium, iron, niacin, riboflavin, thiamin, vitamin A, vitamin C and zinc) from food and supplements combined showed that none were associated with posterior subcapsular cataract, and the only statistically significant association for cortical cataract was niacin intake. But higher intakes of most micronutrients were associated with a lower prevalence of nuclear cataract.

When the odds ratio for nuclear cataract was adjusted for multiple potential cofounders, the trend remained statistically significant for protein, vitamin A, riboflavin, niacin and thiamin. Most odds ratios for the highest intake quintiles were also statistically associated with reduced nuclear cataract prevalence (0.5 for protein, vitamin A and riboflavin; 0.6 for niacin and thiamin).

In addition, the various sources of vitamin A — retinol, beta carotene and carotenoids — were all associated with a lower prevalence of nuclear cataract (odds ratios 0.5 for all three sources, adjusted for multiple variables for the highest intake quintiles). The vitamin E content of foods consumed in Australia is not available from nutritional tables, so the authors were unable to investigate this vitamin.

Finally, there was no statistically significant association between intake of various vegetables (broccoli, Brussels sprouts, cabbage, carrots, cauliflower, green beans, peas and spinach) and nuclear cataract, although the strongest association was for spinach (P for trend = 0.07). In any event, the Australian authors advocate that further research on nutrition and the lens should extend beyond the carotenoids and vitamins E and C.

For Your Information:

• Julie A. Mares-Perlman, PhD, can be reached at Department of Ophthalmology and Visual Sciences, University of Wisconsin, 610 N. Walnut St., 460 WARF, Madison, WI 53705-2397; (608) 262-8044; fax: (608) 263-0279; e-mail: maresp@epi.ophth.wisc.edu.
• Robert G. Cumming, PhD, can be reached at Department of Public Health and Community Medicine, Bldg. A27, University of Sydney, Sydney, NSW 2006, Australia; (61) 2-9351-4822; fax: (61) 2-9351-7420; e-mail: bobc@pub.health.usyd.edu.au. Dr. Cumming has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

References:

• Mares-Perlman JA, Lyle BJ, et al. Vitamin supplement use and incident cataracts in a population-based study. Arch Ophthalmol. 2000;118:1556-1563.
• Cumming RG, Mitchell P, Smith W. Diet and cataract: the Blue Mountains Eye Study. Ophthalmology. 2000;107:450-456.