Because the digestive system has a lot of reserve built into it, aging has less effect on its function than it does on the function of other organ systems. Nonetheless, aging is a factor in several digestive system disorders. In particular, older adults are more likely to develop diverticulosis and to have digestive tract disorders (for example, constipation—see Large intestine and rectum) as a side effect of taking certain drugs.
(See also Overview of the Digestive System.)
With age, the strength of esophageal contractions and the tension in the upper esophageal sphincter decrease (called presbyesophagus), but the movement of food is not impaired by these changes. However, some older adults can be affected by diseases that interfere with esophageal contractions.
With age, the stomach lining's capacity to resist damage decreases, which in turn may increase the risk of peptic ulcer disease, especially in people who use aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs). Also with age, the stomach cannot accommodate as much food (because of decreased elasticity), and the rate at which the stomach empties food into the small intestine decreases. However, these changes typically do not cause any noticeable symptoms. Aging has little effect on the secretion of stomach juices such as acid and pepsin, but conditions that decrease acid secretion, such as atrophic gastritis, become more common.
Aging has only minor effects on the structure of the small intestine, so movement of contents through the small intestine and absorption of most nutrients do not change much. However, lactase levels decrease, leading to intolerance of dairy products by many older adults (lactose intolerance). Excessive growth of certain bacteria (bacterial overgrowth syndrome) becomes more common with age and can lead to pain, bloating, and weight loss. Bacterial overgrowth may also lead to decreased absorption of certain nutrients, such as vitamin B12, iron, and calcium.
With age, the pancreas decreases in overall weight, and some tissue is replaced by scarring (fibrosis). However, these changes do not decrease the ability of the pancreas to produce digestive enzymes and sodium bicarbonate. As the liver and gallbladder age, a number of structural and microscopic changes occur (see Effects of Aging on the Liver).
The large intestine does not undergo much change with age. The rectum does enlarge somewhat. Constipation becomes more common (see Constipation in Adults : Essentials for Older People), which is caused by many factors: