Digestive Function and Aging

// Amy Doyle, MS, CNS

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Digestive Function and Aging

Individuals over the age of 65 seek medical care for gastrointestinal (GI) related complaints more often than any other age group. 1

Digestion is a complex coordination of interactions between mechanical, chemical, and neurological activity, and aging can alter the function of each of these activities. The gastrointestinal tract contains the greatest number of immune cells and is also home to the enteric nervous system (ENS), the largest and most intricate organization of neurons outside the central nervous system. 2 As we age, each organ associated with digestion experiences changes that are a natural part of aging, but which impact overall digestive function.

The Mouth

Adequate mastication and saliva form food into a bolus that can be safely swallowed and is sufficiently disintegrated for the next phase of digestion. Saliva contains two digestive enzymes known as alpha-amylase, which hydrolyzes starches, and lingual lipase, which hydrolyzes triglycerides. Common changes in mastication including tooth loss, trouble swallowing, decreased bite strength, and loss of taste and smell can disrupt this initial stage of digestion by hindering the mechanical breakdown of food and reducing saliva production. This can lead to reduced nutrient assimilation.3Individuals over the age of 65 seek medical care for gastrointestinal (GI) related complaints more often than any other age group.

Next, the reflex response of swallowing propels the bolus of food into the esophagus, where it very quickly progresses toward the stomach with the help of voluntary and involuntary muscle. The involuntary, or smooth muscle, is stimulated by cholinergic nerves which initiate the wave-like motion known as peristalsis. The initial act of swallowing stimulates a drop in pressure at the distal end of the esophagus, relaxing the gastroesophageal sphincter and allowing the bolus of food to pass into the stomach.

The Stomach

The stomach has its own series of chemical, hormonal, and mechanical processes. Gastric juices are released, and multi-directional smooth muscles mix them together with the food resulting in a part liquid/part solid mass known as chyme. The primary players here are hydrochloric acid (HCL), intrinsic factor, and the enzymes alpha-amylase, gastric lipase, and pepsin—an enzyme responsible for hydrolysis of proteins.

However, both HCl and pepsin production have been shown to naturally decline in individuals over the age of 70, which results in the reduced bioavailability of minerals like calcium, magnesium, and iron and impeding the breakdown of proteins. 3,4 Microbial balance in the upper digestive system can be monitored as aging affects this balance.3 Vitamin B12 also requires both pepsin and HCl as they are responsible for the release of free cobalamin from animal proteins.5

The acidic chyme is then moved through the stomach by wavelike contractions, pushing it toward the pyloric sphincter, where gastric emptying into the small intestine occurs.

The Small Intestine

The small intestine is where the majority of nutrient absorption occurs and hormones like secretin and cholecystokinin, and vagal and neural reflexes regulate motility and digestive secretions. Secretin and cholecystokinin stimulate the pancreas to secrete bicarbonate to neutralize acidic chyme and digestive enzymes to digest proteins, carbohydrates and fats. The gallbladder also contracts, releasing bile for the emulsification and absorption of lipids. In elderly patients, cholecystokinin secretion and pancreatic exocrine secretion have both been shown to decrease with age.3

The lumen of the small intestine is lined with mucosa, a membrane layer that serves as a site for nutrient absorption as well as endocrine, enzyme, and immune cell activity. This mucosa is also colonized with intestinal microbiota.

The Mucosa

In addition to lymphoid tissue, the mucosa of the small intestine has an epithelial layer that serves as a barrier between environmental molecules and the bloodstream and adjacent tissue. 2,6 Aging also affects the immune system. 2,7 Age-related cytokine changes include Interleukin-6, a cytokine known for its influence on tight junction proteins and intestinal permeability. 6 Together, immune and cytokine changes affect the structure and composition of intestinal mucosa especially after age 65. 7

Once absorption of nutrients is completed in the duodenum, jejunem, and ileum of the small intestine, the remaining unabsorbed food material passes through the ileocecal valve and enters the large intestine.

The Large Intestine

The large intestine, or colon, is the site where water and residual nutrients like vitamin K, biotin, sodium, chloride, and potassium are absorbed. This is also the site of bacterial fermentation where bacteria act on carbohydrates, generating short chain fatty acids like butyrate-a source of cellular energy. The intestinal effects and microbial changes can impede this process and limit short chain fatty acid production.6

Additional age-related changes

The ENS is essential for its job of regulating GI function via directing activity of other GI cells and thereby controlling gut motility, absorption, secretion and the epithelial barrier.8 Normal age-related neuronal cell death is more predominant in the ENS than in any other place in the body. 8 Particularly susceptible are cholinergenic nerves, which stimulate peristalsis and contraction of smooth muscle.8 Loss of these and other neurons in advanced age has been shown to affect epithelial, muscle and neural function, digestive secretions and bowel transit time.9

Gastrointestinal Restoration Program

Amy Doyle, MS, CNS

Amy Doyle is a board certified nutrition specialist and owner of White Stone Wellness. She graduated from the New York Chiropractic College with her Master’s degree in Applied Clinical Nutrition. She is a member of the American College of Nutrition and American Nutrition Association. She currently has a private practice at Willow Health and Wellness Center in Baldwinsville, NY. Amy helps people with gastrointestinal health, food sensitivities, and metabolic health. Her approach considers the effect of the body on the mind as well as the mind on the body. She is also passionate about the crusade for schools to feed our children healthy, whole foods and is an advocate for establishing community gardens in areas of need.

1. Wade PR.  Aging and Neural Control of the GI Tract: Age-related changes in the enteric nervous system.  Am J Physiol Gastrointest Liver Physiol. 2002. 283: G489-G495
2. Saffrey, Jill M. Aging of the mammalian gastrointestinal tract: a complex organ system.  Age. 2014. 35: 1019-1032
3. Remond, Sharar, Gille et al. Understanding the gastrointestinal tract of the elderly to develop dietary solutions that prevent malnutrition.  Oncotarget. May 2015. 6(16).
4. Keller J, Layer P. The Pathophysiology of Malabsorption. Viszeralmedizin, Gastrointestinal Medicine and Surgery. 2014. 30: 150-4.
5. Andres N, Noel E, et al. Vitamin B12 (cobalamin) deficiency in elderly patients. CMAJ. August 3, 2004. 171(3): 251–259..
6. Mabbot NA. A breakdown in communication? Understanding the effects of aging on the human small intestine epithelium.  Clinical Science. 2015. 129: 529-31.
7. Biagi, Nylund, Candela et al. Through Ageing, and Beyond: Gut Microbiota and Inflammatory Status in Seniors and Centenarians. PLOSone. May 2010. 5(5).
8. Saffrey, JM. Cellular changes in the enteric nervous system during aging. Developmental Biology. 2013. 382: 344-55.
9. Phillips, RJ, Powley, TL. Innervation of the Gastrointestinal Tract: Patterns of Aging.   Auton Neurosci.  October 30, 2007. 136(1-2): 1-19.
 

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