By Will Boggs MD

NEW YORK (Reuters Health) - Calcium supplementation of more than 800 mg/day is associated with an increased prevalence of age-related macular degeneration (AMD), especially in older individuals, according to a cross-sectional study of National Health and Nutrition Examination Survey (NHANES) data.

"Our group had previously found an association between high levels of calcium supplementation and self-reported glaucoma, so it was interesting to also find an association between high levels of calcium supplementation and AMD," Caitlin L. M. Kakigi from University of California, San Francisco, told Reuters Health by email. "We believe this is a novel finding, which, in combination with future longitudinal studies, could significantly impact the care of patients with, or at high risk for, AMD."

About 43% of the U.S. population, including an estimated 70% of older women, say they take calcium supplements. Some earlier studies suggested a role for calcium in the development of AMD, but there have been no studies that directly examined the association between self-reported supplemental calcium intake and AMD.

Kakigi and colleagues used 2007-2008 NHANES data from nearly 3,200 participants to assess the association between AMD assessed by fundus photography and self-reported calcium supplement intake.

The 248 (7.8%) participants diagnosed with AMD were older, on average, than the participants without AMD (67.2 versus 55.8 years, respectively).

Participants in the top quintile of self-reported calcium intake (>800 mg/day) were 85% more likely than participants who did not take calcium to be diagnosed with AMD, the researchers report in JAMA Ophthalmology, online April 9.

The increased risk seemed to be confined to participants aged 68 years or older, where the odds of an AMD diagnosis was 2.63 times higher in those who consumed more than 800 mg/day of calcium than in those who reported no calcium consumption. The association was not significant among those aged 40 through 67 years.

There was no clear dose-response relationship between lower daily levels of calcium intake and AMD risk.

"It is noteworthy that the 800-mg cutoff point for the highest quintile of self-reported calcium intake is below the recommended total daily intake of calcium for men and women in the United States," the researchers say.

"The findings in this study suggest that there is a threshold of calcium supplementation above which there is an increased odds of AMD," Kakigi said. "However, due to the various limitations of our study, and the cross-sectional nature of our data, we cannot make claims of causation regarding calcium supplementation intake and AMD."

"At this time, we do not recommend setting any new specific limits to calcium intake in order to halt the progression or to prevent the development of AMD," she added. "Before we can make any specific recommendations, further longitudinal analyses are needed to understand the relationship between the incidence of AMD and varying levels of calcium intake."

"For those who take calcium to prevent osteoporosis or treat medical conditions, we certainly don't recommend any changes to their therapy," Dr. Shan Lin, director of the lab where the work took place, told Reuters Health. "However, our study may suggest that those with or at significant risk for AMD not take excessive amounts of calcium if there is not a medical necessity for it."

Dr. Paul S. Bernstein from University of Utah School of Medicine's Moran Eye Center in Salt Lake City, told Reuters Health by email, "The association of high calcium intake with elevated risk of AMD would not be predicted based on our current knowledge of AMD pathogenesis and suggests that we need to look more closely at various aspects of calcium homeostasis to better manage our patients at risk for AMD. These novel findings emphasize how much more we still need to understand about the underlying mechanisms of AMD when we make nutritional recommendations to our AMD patients."

"I think this is an interesting and provocative study, but I was disappointed that there was no consideration of vitamin D consumption which influences calcium homeostasis and has been previously associated with a protective effect against AMD," Dr. Bernstein said.

SOURCE: http://bit.ly/1avViTF

JAMA Ophthalmol 2015.