The Boston study compared 188 people with Parkinson’s to 180 people without it. Both groups were composed of people who had the LRRK2 gene mutation and those who didn’t. In addition, 212 research subjects filled out a survey about how much caffeine they consumed each day.
The researchers then looked at not only the amount of caffeine in the participants’ blood, but also other chemicals that are produced as caffeine is metabolized in the body.
“Among people carrying the LRRK2 gene mutation, those who had Parkinson’s had a 76% lower concentration of caffeine in their blood than those who did not have Parkinson’s,” Medical Dialogue wrote. "People with Parkinson’s with a normal copy of the gene had a 31% lower concentration of caffeine in their blood than non-carriers without Parkinson’s.
“Carriers of the gene mutation who had Parkinson’s also had lower consumption of caffeine in their diet. The gene carriers with Parkinson’s consumed 41% less caffeine per day than the people who did not have Parkinson’s, both with and without the gene mutation.”
The Boston study examined participants at only one point in time, Crotty noted, so it isn’t helpful in understanding what effect, if any, caffeine has over time on the risk on Parkinson’s. The study also doesn’t prove caffeine causes a lower risk of Parkinson’s; it only shows an association, she pointed out.