Cholesterol-lowering statins, which are taken by millions of people around the globe at risk from cardiovascular events, could increase the chance of developing cataracts, a large US cohort study has found.

The study - led by researchers at Wilford Hall Ambulatory Surgery Center, in San Antonio, Texas, and funded by the US National Institutes of Health - looked at a large cohort of 6,972 pairs of statin users and non-users, comparing the risk of cataracts between the two groups.

The results, published in the Journal of the American Medical Association (JAMA), found that about a third of both statin users and non-users developed cataracts during the study period, although the risk was slightly higher for the latter group.

However, a separate analysis by the team suggested that the risk of cataracts could be much higher in those taking statins for primary prevention (i.e. in patients at risk from cardiovascular disease who have not yet suffered a related event, such as a heart attack). 

This analysis compared 6,113 healthy statin users (with no co-morbidities) with 27,400 not taking statins. 

After adjusting for various factors, including demographics, medications, and healthcare use, it was concluded that 34% of statin takers were diagnosed with cataracts versus 10% of those not taking cholesterol-lowering medication.

This is not the first time a link between cataracts and statins has been indicated, though prior research into the relationship has been inconsistent. In addition, the study did not factor in whether the type of statin or dosage had any affect on the risk. 

Nevertheless, the researchers stress that “the risk-benefit ratio of statin use, specifically for primary prevention, should be carefully weighed," and have called for further studies to better determine the relationship between their use and cataract development.