Parkinson’s Patients at ‘Significantly’ Lower Risk of Colorectal Cancer

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by Marisa Wexler |

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People with Parkinson’s disease are significantly less likely than those without the neurodegenerative disorder to develop colorectal cancer, a type of cancer that begins in the final part of the digestive tract, a new meta-analysis suggests.

In fact, the analysis showed that the risk of developing such cancer is lowered by more than 20% among Parkinson’s patients in the Americas and Europe. Likely due to a small number of studies, any similar association is “obscure” among Asians with Parkinson’s, the researchers said.

The results were described in “Patients with Parkinson’s disease predict a lower incidence of colorectal cancer,” a study published in BMC Geriatrics.

Colorectal cancer encompasses cancer in the colon, the longest part of the large intestine, and the rectum, which is the very end of the large intestine, ending with the anus. This type of cancer is one of the leading causes of cancer-related deaths worldwide. Indeed, it’s estimated that nearly 1 million people died of colorectal cancer in 2020.

A burgeoning field of emerging research is shedding light on the so-called “gut-brain axis” — essentially, the idea that the health of the digestive tract can have a substantial effect on brain health, and vice versa. Studies have suggested that various gut-related factors — including inflammation and differences among bacteria that live in the digestive system — may be involved in Parkinson’s development and/or progression.

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Given this known link, it is conceivable that some of the processes involved in Parkinson’s and colorectal cancer may be interconnected, according to scientists. Now, a team of researchers at Shanghai Jiao Tong University, in China, performed a meta-analysis to assess the relationship between Parkinson’s and colorectal cancer risk.

“Accumulating epidemiological studies have revealed that patients with PD [Parkinson’s disease] may be associated with a lower risk of certain cancers, however, the association between PD and CRC [colorectal cancer] remains controversial,” the team wrote. “Therefore, we conducted this meta-analysis to provide a quantitative assessment of current epidemiological evidence on CRC in relation to PD and to explore the potential factors affecting the association between the two.”

A meta-analysis is a type of study in which researchers analyze data collected from multiple other previously published scientific reports. By combining data from multiple studies, meta-analyses have more statistical power to find meaningful associations than individual studies.

In total, the researchers analyzed data from 17 studies published between 2000 and 2020. Collectively, these studies included 375,964 people with Parkinson’s and 879,307 cancer patients.

Statistical analyses demonstrated that the risk of colorectal cancer was significantly lowered, by roughly 22%, among Parkinson’s patients.

Further analyses demonstrated that this association was fairly robust for studies done in Europe and the Americas, with a statistically significant “inverse association between [Parkinson’s disease] and [colorectal cancer] in the Western population.”

The association was less strong for studies done in Asia, however, with “contradictory conclusions in published studies.” The researchers said this was likely attributable to a low number of available studies, and substantial variation among those few studies.

“The pooled results for all populations indicated that PD patients have a decreased risk of CRC in Western population. … However, the association in the Asian population remains obscure,” the team wrote. Ultimately, Asians with Parkinson’s disease do seem to have a “modest lower risk” of such cancer, though further studies with less variability is needed for better analysis.

The researchers added that a “key question that our study begs” is the biological mechanism(s) that might link Parkinson’s with colorectal cancer. The team noted several possibilities, such as differences in gut bacteria or in signaling molecules that act throughout the body in both the gut and brain.

“Our research suggests that patients with PD predict a lower risk of CRC. Further studies are warranted to explore the underlying mechanisms of this correlation and to prevention and treatment of both diseases,” the team concluded.

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