BETHESDA--Researchers have shown that taking vitamin C supplements for more than 10 years lowers risk of lens opacities that can lead to cataract surgery in older women.
The study appears in the October issue of the American Journal of Clinical Nutrition, the peer-reviewed publication of the American Society for Clinical Nutrition.
Paul F. Jacques, Sc.D., Scientist and Epidemiologist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, along with 7 colleagues from Tufts and Harvard University, showed that use of vitamin C supplements for more than 10 years was associated with a 77% lower prevalence of early lens opacities and a 83% lower prevalence of moderate lens opacities in a group of women whose average age was slightly over 62-1/2.
As a person ages, cataracts in the eye result from an increasing loss of lens transparency. Opacity, or the condition of becoming opaque, comes from changes in the delicate protein fibers within the eye lens which gradually do not allow clear visual light rays to pass through to the retina. Opacification tends to progress with age. After 65, almost everyone has some degree of cataract formation, but interference with vision is often minor since many opacities are either small or on the edges of the lens.
The study participants were 247 Boston-area women aged 56 to 71 years who were selected from the Nurses Health Study (NHS).
The NHS began in 1976 when 121,700 female nurses, ages 30 to 55 and residing in 11 states, completed a mailed questionnaire on known and suspected risk factors for cancer and heart disease. Every 2 years since 1976, the women have been contacted to provide updated information.
Eligible members of the NHS were ranked according to high or low vitamin C intake, using total consumption (dietary plus supplements) from five prior NHS reports.
"Between 1990 and 1992, we invited about 300 eligible women with the highest and lowest vitamin C intakes to participate in a detailed eye examination," said Dr. Jacques. "In order to detect a relationship in a sample of this size, it was necessary to enrich the group with women either in the high or low consumption categories. But the examiner had no knowledge of the nutrient status of any of the women. The initial examiner's opacity grading for 30% of the women was later checked by a second examiner. There was a 97% agreement rate between the two."
Of the 247 women who had no prior history of cataract and for whom the researchers had complete lens examination data, 59 (24%) had clear lenses, 156 (63%) had early opacities, and 32 (13%) had moderate opacities. Many of the opacities were found in the lens nucleus (nuclear region) of the eye.
Thirteen percent of the women reported taking vitamin C supplements for 1 to 4 years, 18% for 5 to 9 years, and 11% for greater than 10 years. Of the 26 women who took supplements for greater than 10 years, 4 consumed an average of less than 400 milligrams (mg) per day, 12 took an average of 400 to 700 mg per day, and 10 ingested greater than 700 mg per day.
None of the 26 women who had taken vitamin C supplements for longer than 10 years had moderate nuclear cataracts.
"However, we found little evidence that women who took vitamin C supplements for less than 10 years had a lower prevalence of early opacities," said Dr. Jacques.
The investigators adjusted their data relating the duration of vitamin C supplement use to the prevalence of early or moderate opacities by controlling for such factors as age, pack-years smoked (for smokers), body mass index (a measure of body fat), reported summertime sunlight exposure, aspirin use, postmenopausal hormone therapy, and presence of age-related changes in the retina of the eye.
"After adjustment for the potentially confounding variables, the use of vitamin C supplements for greater than 10 years was associated with a substantially lower prevalence of both early and moderate lens opacities at any lens location," said Dr. Jacques.
According to information appearing in this research paper, a recent study indicated that eye tissue may saturate with vitamin C at intakes between 150 and 250 mg per day.
Dr. Jacques commented that future studies of vitamin C and lens opacities should be designed to measure intake for a period greater than 10 years."Shorter periods might result in a failure to observe any beneficial effects of vitamin C on cataract risk," he said.
Jean Mayer Human Nutrition Research Center on Aging at Tufts University, 711
Washington Street, Boston, Massachusetts 02111-1524
Phone: (617) 556-3322
Fax: (617) 556-3344
Journal
American Journal of Clinical Nutrition