Are blood caffeine levels an early indicator of Parkinson's disease?
The disease tends to develop in adults over 60 years of age, and its symptoms are known to worsen over time.
Parkinson's disease affects more than 4 million people globally, and in the United States, around 60,000 new cases are diagnosed yearly, according to data from the National Institutes of Health (NIH).
Previous research has revealed that early diagnosis of Parkinson's disease can lead to improved health outcomes, decelerated symptoms, and preserved neuromotor abilities.
But so far, it has been difficult to diagnose the condition in its early stages, due to the fact that the most obvious symptoms — which are related to motor impairment — become more visible only in the later stages of the disease.
Now, scientists from the Juntendo University School of Medicine in Tokyo, Japan, are investigating the potential of blood caffeine level tests in diagnosing Parkinson's early on.
"Previous studies have shown a link between caffeine and a lower risk of developing Parkinson's disease, but we haven't known much about how caffeine metabolizes within the people with the disease," explains study author Dr. Shinji Saiki.
The researchers' findings were published yesterday in the journal Neurology.
Low blood caffeine points to disease onset
For the study, the team recruited 139 participants, of whom 108 had been living with Parkinson's for an average period of around 6 years, and 31 had not been diagnosed with the disease. The 31 participants without Parkinson's were matched for age.
Dr. Saiki and colleagues performed blood tests on all the participants, measuring levels of caffeine alongside 11 metabolites — that is, byproducts of the metabolization of caffeine.
Additionally, all the participants underwent tests that ascertained whether or not they had any gene variants that impacted how caffeine was processed in their bodies. They were also tested for gene mutations "that can affect caffeine metabolism."
Both the individuals who had a Parkinson's diagnosis and the healthy participants consumed the same amount of caffeine on average: the equivalent of around two cups of coffee per day.
The researchers found that, despite the fact that everyone drank roughly the same amount of coffee daily, the participants with Parkinson's disease had consistently lower blood caffeine levels than their healthy counterparts.
Those with a Parkinson's diagnosis had an average blood caffeine level of 24 picomoles per 10 microliters, and nine out of the 11 metabolites were also discovered in their blood.
By contrast, the healthy participants measured 79 picomoles per 10 microliters, on average. Also, a metabolite that the researchers tested for — 1,3,7-trimethyluric acid — was present in levels that were below those observable in over 50 percent of the participants with Parkinson's.
The statistical analysis performed by Dr. Saiki and his colleagues suggested that the blood caffeine assessment was a reliable way of diagnosing the disease, scoring 0.98 out of 1, where 1 stands for a correct diagnosis in all cases.
When testing for the impact of gene mutations on caffeine metabolism, the researchers found no differences between the participants with and without Parkinson's disease.
Another important finding, emphasized by Dr. David G. Munoz — from the University of Toronto in Canada — in the editorial that accompanies the paper, is that the participants who had reached a more severe stage of the disease did not have significantly lower blood levels of caffeine.
This, explains Dr. Munoz, suggests that the difference may be specific to the earlier stages of Parkinson's disease.
'An easy test for early diagnosis'?
Nevertheless, the new study faces certain limitations — including the fact that no individuals with a severe form of Parkinson's disease participated.
This may have impacted the test's capacity to point to any links between caffeine levels in the blood and the severity of the condition.
Another limitation pointed out by Dr. Munoz was that those with a Parkinson's diagnosis were all taking medication for this condition throughout the period in which the study was conducted.
This could mean that the way in which the bodies of those with Parkinson's metabolize caffeine could be affected by the action of the prescribed drugs.
However, as Dr. Munoz explains, "If [the study's] results can be confirmed, they would point to an easy test for early diagnosis of Parkinson's, possibly even before symptoms are appearing. This is important because Parkinson's disease is difficult to diagnose, especially at the early stages."