When the study started, they had no signs of eye problems. Over the next eight years, 258 of them developed diabetic retinopathy -- the medical term for damage to the blood vessels in the retina, the lining of tissue at the back of the eye. Left untreated, it can lead to loss of sight.
"Those who ate the most fruit were the least likely to develop diabetic retinopathy," says study head Shiro Tanaka, PhD, of Kyoto University Hospital.
People who ate an average of 9 ounces of fruit a day had half the risk of developing the eye condition over the eight-year period, compared with those who ate less than an ounce a day, the study showed. The odds were about 40% lower for people who ate an average of 3 to 5 ounces of fruit a day, compared with those who ate less than an ounce a day.
However, the study does not show cause and effect. It shows a link between eating more fruit and lower risk of diabetic retinopathy, but it does not prove that fruit prevented the eye disease.
Don't think of your fruit in terms of ounces? For comparison, a medium apple, orange, or pear weighs about 6 ounces, a banana about 5 ounces.
Nutrients May Work Together
The various vitamins and other nutrients in fruit probably work together to protect against eye complications, says April Carson, PhD, MSPH, of the University of Alabama. She wasn't involved in the study, but chaired a session at the American Diabetes Association's annual meeting, at which the study was presented.
Carson tells WebMD that the study has several strengths. For starters, the study followed people over time, rather than looking back at medical records to see how many people developed eye problems, she says.
Also, the analysis took into account other major risk factors for diabetic retinopathy, including age, sex, blood sugar levels, smoking and drinking habits, weight, and physical activity, Carson says.
The major caveat: Most people in the study ate a low-fat diet. That means the results may not apply to people who get more fat in their diet, Tanaka says.
Nearly 30% of U.S. adults with diabetes have diabetic retinopathy, and 4.4% have vision-threatening diabetic retinopathy, according to a CDC study from 2010.
These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.