The digestive system is less affected by aging than other body systems. This system includes the mouth, oral cavity, esophagus, stomach, small intestine, large intestine (colon), rectum, liver and pancreas.
Let’s start by discussing changes in the mouth and oral cavity. Aging causes the gums to thin and recede, which exposes teeth and increases the risk of developing cavities. Seniors have less ability to chew food because of diminished muscle mass. Many older people have an impaired transfer of the food bolus from the mouth to the back of the tongue and into the esophagus, conferring a greater risk for aspiration of food. Up to 40% of older people complain of dry mouth although the symptom is often due to side effects of medications.1
Sense of taste and smell falls off significantly with age. The ability to discriminate between sweet, sour, salty, and bitter decreases. The thresholds for salty and bitter taste increase with age but the threshold for sweet remains the same. Sense of smell also decreases progressively after age 50, often resulting in a significantly impaired ability to smell by age 80.2 Smell and taste are strongly connected. When you are unable to smell your food, your sense of taste diminishes as well. These individuals will not enjoy their food as they did when they were younger.
The force of muscle contractions in the esophagus decreases but most older individuals are able to move the food bolus normally down the esophagus and into the stomach. There is a bundle of muscles at the lower end of the esophagus next to the stomach called the lower esophageal sphincter (LES). Normally the LES prevents the backflow of acidic stomach juice into the esophagus which can cause symptoms of heartburn. As we get older the muscles of the LES weaken which allows more acidic stomach juice to flow backwards into the esophagus. This may explain why episodes of gastroesophageal reflux disease (GERD) tend to last longer in older people.
Another factor that can make heartburn more severe is the presence of a hiatal hernia. A hiatal hernia occurs when the upper part of the stomach moves above the diaphragm and into the chest cavity where the esophagus is located. Hiatal hernias are found in 60% of people over the age of 60.3
Aging also affects the stomach. Solid foods are moved through the stomach at a normal rate but liquids take longer to transit into the small intestine. This phenomenon, known as a prolonged gastric emptying rate, can sometimes cause early satiety or nausea. The wall of the stomach is more likely to become inflamed (gastritis) and the stomach lining becomes more sensitive to irritants like nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or naproxen. These medications can erode the stomach lining and cause ulcers. In addition, over 50% of seniors are infected with a stomach bacteria called Helicobacter pylori.4 This chronic infection is often asymptomatic but sometimes can cause ulcers in the stomach lining. Unfortunately, older individuals also have a slower rate of ulcer healing.
Aging doesn’t change your desire to eat before a meal, but older people experience less hunger and desire to eat after consuming food compared with younger people. Changes in hormone levels can explain this. Levels of satiety hormones such as cholecystokinin (CCK), leptin and glucagon-like peptide-1 (GLP-1) increase in older people while levels of hunger hormones like ghrelin decrease.
In the small intestine, 90% of the digestion and absorption of food occurs. Carbohydrates, fats, proteins, vitamins, minerals and water are absorbed from food and move into the bloodstream here. Older people are able to absorb most nutrients normally although they are less able to absorb calcium and zinc. Typically, women over age 75 absorb 25% less of a given dose of calcium than younger women.5 Apart from aging, common medications such as metformin may impair absorption of vitamin B-12 in the small intestine.
In the next article we will examine the age-related changes in the colon, rectum, liver and pancreas.
References
- Fillit, H., Rockwood, K., & Young, J. B. (2016). Brocklehurst’s Textbook of Geriatric Medicine and Gerontology. Berlin: Elsevier.
- Doty RL, Shaman P, Applebaum SL, Giberson R, Sikorsky L, Rosenberg L. Smell identification ability: changes with age. Science. 1984;226:1441–3.
- Grande L. Deterioration of esophageal motility with age: a manometric study of 79 healthy subjects. Am J Gastroenterol. 1999; 94: 1795-1801.
- Marshall BJ. Helicobacter pylori. Am J Gastroenterol. 1994; 89: S116-28.
- Salles N. Basic mechanisms of the aging gastrointestinal tract. Dig Dis. 2007; 25(2): 112.