The large intestine, or colon, is the final major segment of the digestive tract (CCS 2015). Waves of muscular contractions called peristalsis propel fecal material through the colon (Leung, Riutta 2011). These muscular activities are coordinated by signals from the nervous system and neurohormones like histamine and serotonin (Lee 2014; Wood 2007). Colonic peristalsis is naturally strongest upon waking in the morning and after meals, and insufficient peristalsis leads to constipation (Yu 2014; Hendricks 1997).
The Gut-Brain Axis
The network of nerves that controls gut activity, known as the enteric nervous system, contains as many nerve cells as the spinal cord (Wood 2007; Daulatzai 2014). The enteric nervous system and central nervous system are functionally interdependent. In other words, dysfunction originating in the central nervous system can give rise to problems in the enteric nervous system, and dysfunction originating in the enteric system may compromise central nervous function (De Palma 2014).
This reciprocal relationship between the gastrointestinal tract and the nervous system has been called the “gut-brain axis” (Daulatzai 2014; O'Malley 2011; Lee 2014; De Palma 2014). Functional (primary) constipation is thought to involve gut-brain axis dysfunction (De Palma 2014). Bi-directional dysfunction of this axis also contributes to irritable bowel syndrome (Daulatzai 2014; O'Malley 2011; De Palma 2014).
Researchers have found especially strong correlations between chronic constipation and two chronic neurological diseases: Parkinson’s disease and Lewy-body dementia (in which abnormal protein deposits called Lewy bodies build up in brain cells) (Idiaquez 2011; Postuma 2013; Weerkamp 2013). In one study, older individuals with a history of chronic constipation were more than three times as likely to develop Parkinson’s disease during an average 5.5 years of follow-up, and those with the most severe constipation had the greatest risk (Lin 2014). Other neurological diseases that have been correlated with constipation include restless leg syndrome (Shneyder 2013) and Alzheimer’s disease (Zakrzewska-Pniewska 2012).
Inflammation is thought to underlie the connection between constipation and neurological disease. Disruptions in the gut microenvironment contribute to gastrointestinal symptoms as well as neurological problems; degradation of the gut barrier promotes systemic inflammation, which in turn promotes neuroinflammation and subsequent cognitive dysfunction (Daulatzai 2014).