"Oxidative damage of the eye lens caused by free radicals has been suggested to be crucial in development of cataracts," said Susanne Rautiainen of the Institute of Environmental Medicine at the Karolinska Institutet, who led the study.
Her team looked at the diets of more than 30 000 middle aged and older women, and found those with the highest total intake of antioxidants had about a 13% lower risk of developing cataracts than women who consumed the least. "Previous studies have focused on individual antioxidants obtained from the diet or supplements and they have reported inconsistent results," Rautiainen said.
"However, in diet much wider ranges of antioxidants are present than those studied previously." Instead of looking at single antioxidants, such as vitamins C and E, and plant flavonoids such as lycopene, the researchers used a measure of total antioxidant values in foods, which takes into account how the nutrients work together.Read: Ten sources where you can obtain antioxidants
Foods high in antioxidants
For the study, more than 30 000 Swedish women over age 49 were observed for about 7 years for signs of developing cataracts, and were given a dietary questionnaire.
Foods high in antioxidants include coffee, tea, oranges, whole grains and red wine. Based on total antioxidant consumption, the researchers divided the women into five groups, ranging from the greatest antioxidant intake to the least. Among those who ate the most antioxidants, 745 cases of cataract were recorded, compared to 953 cases among women with the lowest antioxidant consumption.
The results were published in JAMA Ophthalmology. Women who ate more antioxidants also tended to be more educated and were less likely to smoke.
More than 20 million Americans aged 40 years and older have cataracts, which cause clouded vision and eventually blindness, in one or both eyes, according to the US Centres for Disease Control and Prevention."The results are not that surprising," William Christen said.
Christen, of Brigham and Women's Hospital and Harvard Medical School in Boston, studies eye diseases and vitamins and was not involved in the new study.Read: More people are getting cataracts
Limitations of study
The findings are in line with previous research suggesting antioxidants may help protect against cataracts, but the study has limitations, he cautioned. "The women participants simply reported on a questionnaire the food choices they made over the past year," Christen said.
"As an observational study, there is always concern that women who choose healthier diets may also differ in other important ways, like body weight, smoking habits, aspects of the diet other than antioxidants that may be more directly related to cataract risk." Rautiainen suspects the results would be similar among men and in other countries, but can't say for sure until those studies have been done.
Colourful fruits and vegetables are the best source of antioxidants for people who want to increase their intake, she said. "Results of numerous observational studies have suggested a possible beneficial role for high antioxidant intake in a number of age-related disorders," Christen said.
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