Contrast agents used in X-ray and other methods of imaging could increase the risk of developing dementia by 2.09 times, researchers said yesterday.

Contrast agents are widely used in clinical testing to increase the contrast of structures or fluids within the body for imaging, such as computerized tomography (CT) or magnetic resonance imaging (MRI) scans.

According to National Health Insurance Administration (NHIA) data, contrast agents are administered to about 305,000 people annually for CT or MRI scans, with the number increasing every year.

Building on previous evidence suggesting that contrast agents could increase the risk of blood clots by harming the kidneys, the National Health Research Institutes (NHRI) and Taichung Veterans General Hospital conducted a study to investigate any potential correlation between the imaging aids and dementia.

From 11.33 million National Health Insurance card holders, researchers paired nearly 3 million people for analysis after matching variables, half of whom had been administered contrast agents within the previous 10 years.

They found that those who had been administered a contrast agent were 2.09 times more likely to develop dementia than those who had not after adjusting for age, sex and other conditions.

The risk of developing vascular dementia was up to 4.7 times higher, the findings showed.

“Contrast agents should only be used when necessary,” NHRI Institute of Population Health Sciences Deputy Director Hsu Chih-cheng (許志成) told a news conference announcing the results of the study yesterday.

There is no such thing as an entirely safe agent, but if they could be used sparingly and in small quantities by intravenous injection, and if patients drink plenty of water before the test, it could reduce their negative effects on the body, Hsu said.

Some tests require the use of contrast agents, and people who take such tests should be screened for dementia over the following decade, Hsu said.

Hsu also urged doctors to be more cautious in their use of contrast agents, and said patients should consult with their doctor before taking an X-ray-based exam to weigh risk against necessity.

The research is not intended to scare people, but to inform medical practitioners to use contrast agents with caution, said Wu Ming-ju (吳明儒), head of the hospital’s Department of Internal Medicine.

About 10,000 people begin long-term dialysis every year, 24 percent of whom are administered contrast agents before starting, Wu said.

The study was published in the journal Biomedicines in August.