Clinical meaning
Aging produces significant physiological changes across multiple organ systems that directly impact nutritional status, dietary requirements, and the ability to maintain adequate nutritional intake. In the gastrointestinal system, gastric acid secretion decreases (hypochlorhydria and achlorhydria) beginning around age 50, reducing the absorption of iron, calcium, vitamin B12, and folate. Decreased intrinsic factor production further impairs vitamin B12 absorption, placing elderly individuals at risk for megaloblastic anemia and neurological complications (peripheral neuropathy, dementia-like symptoms). Gastric emptying slows, contributing to early satiety and reduced food intake. Intestinal motility decreases, increasing constipation risk, while the intestinal mucosal surface area decreases, reducing overall absorptive capacity. The liver decreases in size and blood flow by approximately 30 to 40% after age 65, affecting first-pass metabolism of medications and synthesis of albumin and other proteins. Hepatic cytochrome P450 enzyme activity declines, prolonging the half-life of many medications and increasing drug interaction risks. In the renal system, glomerular filtration rate (GFR) decreases approximately 1 mL/min/year after age 40, reducing the kidney's ability to concentrate urine and conserve sodium, increasing dehydration risk. The thirst mechanism becomes blunted with...