Iron and Calcium Intake Linked to Glaucoma Risk

High intake of total calcium and iron appear to be associated with greater odds of self-reported glaucoma, according to a new study.

Researchers at the University of California, San Francisco (UCSF; USA) examined dietary surveys from US National Health and Nutrition Examination Survey (NHANES) participants for the years 2005 to 2008, which included 6,316 persons aged 40 years and older, 422 of whom developed glaucoma. They then estimated usual intake of calcium and iron on the basis of multiple measures of 24-hour recall, classifying them into quintiles. Age, sex, race, and comorbidities--including osteoporosis and anemia--were entered into the multivariate logistic regression model to produce an adjusted odds ratio for self-reported glaucoma.

The results showed that total calcium and iron intake (which included both dietary and supplement intake) were associated with increased risks. For total iron intake, odds ratios were 2.95 for the 4th quintile and 1.58 for the 5th, compared with 1.13 for the 2nd and 0.95 for the 3rd quintiles. For total calcium intake, odds ratios were 1.58 for the 4th quintile and 1.26 for the 5th, compared with 1.14 for the 2nd and 1.21 for the 3rd quintiles. But when the researchers analyzed the nutrients in foods alone, odds ratios for dietary iron progressively diminished as intake lessened, from 0.82 for the 2nd quintile to 0.39 for the 5th. A similar decline was seen for dietary calcium. The study was presented at the American Academy of Ophthalmology (AAO) annual meeting, held during November 2012 in Chicago (IL, USA).

“We think that supplement use is driving the difference, but because of limitations in this methodology, we could not isolate supplement use. Based on these results and previous studies, we can hypothesize that high total intakes of calcium or iron, driven by supplement use, may serve as potential environmental stressors,” said study presenter and coauthor Sophia Wang, MD. “This, combined with a background of already impaired calcium or iron homeostasis due to aging or other factors, may lead to damage of the trabecular meshwork or ganglion cell death, thus ultimately increasing the risk of glaucoma.”

Glaucoma is an eye disease in which the optic nerve is damaged due to loss of retinal ganglion cells in a characteristic pattern, and is the second-leading cause of blindness after cataracts. It is normally associated with increased fluid pressure in the eye (aqueous humor). Glaucoma has been called the "silent thief of sight" because the loss of vision often occurs gradually over a long period of time, and symptoms only occur when the disease is quite advanced. Once lost, vision cannot normally be recovered, so treatment is aimed at preventing further loss.

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