What causes altered taste in adults, particularly in those with underlying medical conditions such as diabetes, kidney disease, or neurological disorders?

Altered Taste: Causes and Clinical Approach

Altered taste in adults results primarily from medications (the most common cause at 21.7%), followed by zinc deficiency (14.5%), oral diseases (7.4%), and systemic diseases (6.4%), with physiological aging, neurological conditions, and chronic diseases further compounding these effects. 1

Primary Mechanisms of Taste Alteration

Medication-Induced Taste Disorders

• Medications are the single most significant contributor to taste disorders in elderly patients, particularly through drug-drug interactions that increase systemic drug concentrations to supratherapeutic levels. 2
• Drug-drug interactions inhibit P-glycoprotein efflux transporters and cytochrome P450 metabolism, causing intravascular taste disturbances and altered taste cell biochemistry. 2
• Up to 11% of elderly persons using multiple medications report taste aberrations. 3
• Acetylcholinesterase inhibitors (used in Alzheimer's disease) can worsen taste perception by increasing saliva production and altering oral environment. 4
• Anticholinergic medications exacerbate taste dysfunction through multiple mechanisms affecting taste receptor function. 4

Age-Related Physiological Changes

• Sense of taste diminishes with increasing age due to physiological changes, disease, and medication use, leading to increased salt use to compensate for reduced palatability. 5
• Changes in taste perception occur with aging as a normal physiological process, independent of disease states. 5
• Age-related taste decline affects the ability to detect all five basic flavors (salty, sweet, sour, bitter, and umami), each serving specific nutritional functions. 1

Nutritional Deficiencies

• Zinc deficiency accounts for 14.5% of taste disorders and is particularly common in elderly populations with multiple chronic conditions. 1
• Micronutrient deficiencies (particularly B vitamins and zinc) are common in elderly patients and directly impact taste receptor regeneration and function. 5
• Alcohol intake ≥10 g/day is independently associated with increased taste thresholds and taste loss. 6

Systemic Disease States

• Diabetes mellitus affects parasympathetic innervation and can alter taste perception through autonomic dysfunction. 7
• Chronic kidney disease causes salivary disorders with altered composition affecting taste sensation. 7
• Cerebral disease is independently associated with elevated taste thresholds. 6
• Cancer, gastrointestinal inflammatory disorders, and other chronic conditions directly impact nutritional status and taste function. 5

Neurological Disorders

• Progressive neurologic diseases (Parkinson's disease, dementia, stroke, multiple sclerosis, ALS) cause taste alterations through both direct neural pathway damage and secondary effects on swallowing and oral clearance. 4
• Parkinson's disease causes bradykinesia affecting oral and pharyngeal function, leading to saliva pooling and altered taste perception. 7
• Stroke affects taste pathways in 50% of patients with clinically significant dysphagia. 7
• Multiple sclerosis causes dysphagia in over one-third of patients, affecting taste through impaired oral clearance. 7

Oral and Dental Pathology

• Chronic dental diseases, atrophic glossitis, and oral infections directly impair taste receptor function and are common in elderly populations. 5, 6
• Poor dental hygiene and high intake of sugars/refined carbohydrates increase risk of dental disease affecting taste. 5
• Oral thrush and other infections alter the oral environment and taste perception. 6
• Peptic esophagitis from GERD affects 8-19% of adults and can cause taste disturbances. 4

Clinical Assessment Algorithm

History Taking Priorities

• Document all current medications with specific attention to recent additions or dose changes, as medications are the most modifiable cause. 2, 1
• Quantify alcohol consumption (threshold ≥10 g/day associated with taste loss). 6
• Assess for specific taste complaints: hypogeusia (diminished taste), ageusia (absent taste), aliageusia (food-related distortion), or phantogeusia (taste illusions). 3
• Screen for neurological symptoms: bradykinesia, tremor, cognitive changes, prior stroke, or progressive weakness. 7, 4
• Evaluate nutritional intake patterns and unintentional weight loss (>5% in 3 months indicates severe risk). 8

Physical Examination Focus

• Examine oral cavity for atrophic glossitis, thrush, dental disease, and mucosal abnormalities. 6
• Assess performance status and functional capacity. 6
• Evaluate for signs of systemic disease: diabetes, kidney disease, neurological deficits. 7, 4

Laboratory Evaluation

• Measure serum zinc levels, as zinc deficiency is the second most common cause and is treatable. 1
• Check mean corpuscular volume (MCV), as elevated MCV independently predicts taste loss. 6
• Assess for B vitamin deficiencies (particularly B12 and folate) in at-risk populations. 5
• Screen for diabetes and renal function in appropriate patients. 7

Management Strategy

Medication Review (First Priority)

• Conduct scrupulous drug screening and consider switching medications within the same class when possible, as this is the most common and modifiable cause. 3, 1
• Review for drug-drug interactions affecting P-glycoprotein and cytochrome P450 systems. 2
• Periodically review pharmacological therapies in elderly patients on multiple medications. 1

Nutritional Interventions

• Administer zinc replacement therapy (proven to enhance taste for sweet, bitter, and salty flavors) when deficiency is documented. 3
• Consider niacin and vitamin A supplementation, which ameliorate hypogeusia and dysgeusia. 3
• Provide dietary counseling to limit cariogenic foods and reduce salt intake to <6 g/day. 5
• Use herbs and spices as salt alternatives rather than salt substitutes (which contain high potassium/sodium). 5

Palliative Measures

• Recommend mints, sugarless chewing gum, and bicarbonate mouthwashes for symptomatic relief. 3
• Avoid flavor enhancers as routine intervention, as evidence does not support systematic use. 5
• Ensure adequate hydration (women ≥1.6 L/day, men ≥2.0 L/day) to maintain saliva production. 5

Dental and Oral Care

• Provide specific dietary advice for edentulous patients and those with dental disease. 5
• Treat oral infections and improve dental hygiene. 5, 6
• Reduce frequency of snacking and intake of sticky, cariogenic foods. 5

Critical Clinical Pitfalls

• Do not dismiss taste complaints as "normal aging" without investigating medication causes and nutritional deficiencies, as these are highly modifiable. 3, 1
• Do not overlook the serious nutritional consequences: taste loss leads to food anhedonia, decreased calorie intake, and unintentional weight loss, particularly dangerous in elderly patients. 3
• Recognize that patients with diabetes, heart failure, or hypertension requiring salt restriction face particular challenges when taste diminishes. 5
• Remember that full recovery from taste disorders may take several months even after removing the offending cause. 9
• Include gustatory function assessment in comprehensive geriatric evaluations, especially for hospitalized, institutionalized, or malnourished elderly patients. 1
• Consider that viral infections, head injuries, and nasal obstructions commonly cause smell disorders that patients may describe as taste problems. 9