A new study published in the issue of Neurology revealed that testing the level of caffeine in the blood might support the diagnosis of Parkinson's disease. The study found that people with Parkinson's disease had considerably lower levels of caffeine in their blood than people without the disease, although they consumed the same amount of caffeine.

Earlier studies have shown that caffeine linked with a lower risk of developing Parkinson's disease. However, the team have not known much about how caffeine metabolizes within the people with Parkinson's disease.

People in the study with more severe stages of the disease did not have lower levels of caffeine in the blood, suggesting that the decrease occurs from the earliest stages of the disease.

If the results can be confirmed, the researchers would identify 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 in the early stages.

The study involved 108 people who had Parkinson's disease for an average of about six years and 31 people of the same age who did not have the disease. Their blood was tested for caffeine and for 11 byproducts the body makes as it metabolizes caffeine.

The research team also tested for mutations in genes that can affect caffeine metabolism. The two groups consumed about the same amount of caffeine, with an average equivalent to about two cups of coffee per day.

The results showed that the people with Parkinson's disease had significantly lower blood levels of caffeine and nine of the 11 byproducts of caffeine in the blood. The caffeine level was an average of 79 picomoles per 10 microliters for people without Parkinson's disease.

People with the disease had 24 picomoles per 10 microliters. For one of the byproducts, the level was below the amount that could be detected in more than 50% of the people with Parkinson's disease.

In the statistical analysis, the researchers found that the test could be used to reliably identify the people with Parkinson's disease, with a score of 0.98 where a score of 1 means that all cases are identified correctly.

In the genetic analysis, there were no differences in the caffeine-related genes between the two groups. However, people with severe Parkinson's disease were not included, which could affect the ability to detect an association between disease severity and caffeine levels.

In conclusion, the findings showed that the people with Parkinson's disease had significantly lower blood levels of caffeine and nine of the 11 byproducts of caffeine in the blood. The noted that all of the people with Parkinson's were taking Parkinson's medication and it is possible that the drugs could affect the metabolism of caffeine.