Opposite Results: Do Calcium Supplements Increase Macular Degeneration Risk?

Previous studies have pointed to daily calcium doses 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?

More than 40% of the U.S. population, including 70% of older women, say they take calcium supplements.

In the first study showing a relationship, researchers found that those who were in the top 25% of self-reported calcium intake (>800 mg/day) were 85% more likely than participants 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 research, the researchers determined that as people got older, an association between calcium intake and macular degeneration risk reduction emerged. 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 for both healthy patients and those with macular degeneration. It found a clear 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 that risk was increased.

The study showing 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 showed that high dietary calcium did 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.