April 10, 2015 -- Older people who take more than 800 milligrams of calcium a day are almost twice as likely to be diagnosed with age-related macular degeneration (AMD), a condition that causes severe vision loss, according to a new study in JAMA Ophthalmology.

The link was found only in people 68 and older.

The research doesn’t prove cause and effect, says Rahul Khurana, MD, a spokesman for the American Academy of Ophthalmology. He wasn’t involved in the study.

Researchers from the University of California, San Francisco, evaluated 3,191 people ages 40 and older who were participating in a national health survey. The group included 248 people diagnosed with AMD. Each participant was asked about using dietary supplements and antacids.

The researchers say their results held true after they accounted for things like:

Age

Sex

Ethnicity

Smoking

Drinking alcohol

Obesity

Cataract surgery

Glaucoma

High blood pressure

Stroke

Heart disease

One limitation of the study is that it’s possible some of the participants didn’t accurately report their use of calcium supplements. Also, the researchers say they didn’t look into what if any role calcium from foods and drinks might play.