Which is it? Calcium does or doesn't increase macular degeneration risk?

A previous study pointed to high daily calcium dosage being linked to increased risk of macular degeneration, a potentially blinding condition of the eye. But a new National Institutes of Health study states that calcium supplementation is not a risk.

So who are we to believe?

It's an important issue, because more than 40% of the U.S. population, including 70% of older women, take calcium supplements.

In the first study showing a relationship, researchers found that those who reported taking more than 800 mg/day of calcium were 85% more likely than those who did not take calcium to be diagnosed with macular degeneration. The study was published in JAMA Ophthalmology in 2015.

This month's study by the National Eye Institute came to a completely different conclusion. Re-evaluating 4,751 participants in their previous AREDS study, the researchers determined that people with the highest intake of calcium from dietary or supplement sources had a lower risk of developing late-stage macular degeneration compared with those in the lowest calcium intake groups.

The difference in the results of these studies are in HOW they were performed.

The first study showing an adverse effect evaluated both healthy patients and those with macular degeneration. It found a relationship between high calcium intake and the development of macular degeneration. However, the authors were clear to state that it was not a dose-response effect, meaning that each milligram extra calcium that a person ingested didn't proportionally increase the risk. Rather, there was a threshold level (more than 800 mg/day) that increased the risk.

The more recent study showing that calcium was not harmful looked at patients who already had macular degeneration and sought to find a dose-response effect, and found none. They then concluded that there was no relationship.

Can both studies be correct? Yes.

Taking 800 mg per day of calcium increases your risk of developing macular degeneration if you have none. But if you already have macular degeneration, taking 1,000 mg per day of calcium rather than 500 mg will not increase the risk of progression to a severe form.

What do I advise my patients? 

This Harvard University article explains that high dietary calcium does not materially increase bone density or reduce the risk of fractures.

So play it safe, and don't take more than 800 mg calcium per day.

Paul Krawitz, M.D., President and C.E.O
Vitamin Science, Inc.

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