Salivary Caffeine Levels Decreased in Some Patients

People with moderate or advanced Parkinson’s disease have abnormally low levels of caffeine in their saliva, despite normal caffeine metabolism, a new study indicates.

The findings suggest that measuring caffeine in saliva could be useful for gauging Parkinson’s disease progression.

The study, “Salivary caffeine in Parkinson’s disease,” was published in Scientific Reports.

Prior research has suggested that caffeine may affect the course of Parkinson’s disease. However, the relationship between bodily caffeine levels and Parkinson’s — especially early on in the disease — is not completely understood.

In the study, a team of researchers based in Italy measured caffeine levels in the saliva of 86 people with Parkinson’s, as well as 83 individuals without Parkinson’s (healthy subjects). Among the Parkinson’s patients, 39 had early mild disease, while 47 had moderate or advanced Parkinson’s.

The researchers noted that saliva samples were used because they are relatively easy and noninvasive to collect.

There were no significant differences between the Parkinson’s patients as a whole and healthy subjects in terms of salivary caffeine levels. Comparisons between people with early Parkinson’s and healthy subjects also showed no significant differences.

However, individuals with moderate or advanced Parkinson’s had significantly lower levels of caffeine, compared to healthy subjects (1.13 vs. 2.13 micrograms per ml). Those with moderate or advanced disease also had significantly higher caffeine absorption, but they had similar activity of the enzyme that metabolizes caffeine.

Salivary caffeine levels also showed a significant negative correlation with disease severity and duration. In other words, people with Parkinson’s who had lower levels of caffeine in their saliva were statistically more likely to have more severe disease, and to have been living with Parkinson’s for longer.

Additional analyses among only Parkinson’s patients with moderate/advanced disease showed that, compared to those without, individuals with motor complications had significantly lower levels of salivary caffeine.

“The result that salivary caffeine was only reduced in moderate/advanced PD [Parkinson’s disease] patients, and that disease duration and severity correlated with decreased caffeine levels strongly support the hypothesis that caffeine levels in PD are a marker of disease progression,” the researchers wrote. “This hypothesis is also supported by our finding that the presence of motor complications was associated with lower basal caffeine levels, even after adjusting for caffeine intake, disease duration, and severity.”

Various other statistical analyses to control for factors that might have affected the results — ranging from coffee intake, to medications, to age and sex — found generally consistent results.

“The correlation we found between salivary caffeine levels and PD severity and duration suggests that salivary caffeine may be a biomarker of disease progression that provides new insight into PD pathogenesis [disease processes],” the researchers concluded.