GI Nutrition: Minerals and Trace Elements

0:00Welcome to Board Pearls. This is episode four of four of the GI Nutrition chapter, in the Special Populations and Acute or Supportive Care module. In this episode we cover the mineral and trace-element deficiencies: iron, PPI-induced hypomagnesemia, zinc acrodermatitis with altered taste, copper myeloneuropathy especially from zinc excess, selenium cardiomyopathy, and the manganese and chromium problems of long-term parenteral nutrition.

0:27The last episode read the vitamins by their recognition cues. The minerals and trace elements run on the same logic: each element has a specific biochemical role and a specific exposure or pathology context that produces its phenotype. The boards favor the pairs that turn on a single mechanism. Zinc induces metallothionein and traps copper. Cholestasis blocks biliary manganese excretion. Brazil nuts concentrate selenium.

0:52Iron deficiency in this chapter is a frame for chronic GI blood loss, celiac disease with proximal villous atrophy, post-bariatric anatomy that bypasses the duodenal absorption site, and increased demand from pregnancy or growth. Repletion is oral ferrous sulfate or intravenous iron when oral is not tolerated or absorbed, with reticulocyte response within seven to ten days and hemoglobin recovery over weeks.

1:22PPI-induced hypomagnesemia carries an FDA warning that was issued in 2011. The mechanism is impaired TRPM6 channel function in the distal convoluted tubule under chronic gastric acid suppression. The exact molecular link between gastric pH and TRPM6 is incompletely understood, but the clinical signature is symptomatic hypomagnesemia in a long-term PPI user with normal renal function and without obvious diuretic or alcohol cause. The symptoms are tetany, seizure, and arrhythmia. The most testable feature is the kinetic asymmetry. Magnesium normalizes within roughly one week of PPI discontinuation, but recurs within roughly two weeks of PPI rechallenge. That asymmetry is the answer to a recognition stem. Treatment is PPI discontinuation when feasible and magnesium repletion. Outpatients receive oral magnesium oxide or magnesium chloride. Symptomatic hospitalized patients receive intravenous magnesium sulfate. Vonoprazan or another potassium-competitive acid blocker is an alternative that does not produce hypomagnesemia.

2:30Zinc deficiency. The recognition phenotype is acrodermatitis enteropathica, with periorificial dermatitis around the mouth and nose, alopecia, diarrhea, impaired wound healing, dysgeusia, and immune dysfunction. The inherited form presents in infancy after weaning from breast milk to formula, because breast milk has a zinc-binding ligand that supports absorption in patients with a defect in the SLC39A4 zinc transporter. The acquired form appears in the same nutritional populations that produce most micronutrient deficiencies. Short bowel syndrome. Severe Crohn disease. Alcohol use disorder. Celiac disease. Prolonged unsupplemented parenteral nutrition. Altered taste, or dysgeusia, is the cue that gets overlooked. Patients describe food as bland or metallic, and the symptom resolves with repletion. In cirrhotic patients, refractory hepatic encephalopathy can reflect zinc deficiency because zinc is a cofactor for ornithine transcarbamylase in the urea cycle. Repletion is oral zinc sulfate two hundred twenty milligrams, which is fifty milligrams of elemental zinc, daily. The infant form requires lifelong supplementation. Monitoring matters because zinc excess itself produces complications.

3:47Copper deficiency is the inverse problem with zinc, and the linkage between them is the highest-yield trace-element pair on the boards. Chronic zinc excess, from older denture cream formulations that contained substantial zinc, from excessive supplementation, or from industrial exposure, induces enterocyte metallothionein. Metallothionein binds copper preferentially over zinc and traps copper inside the enterocyte. The enterocyte is shed before transferring copper to portal blood. So zinc excess in the lumen produces copper deficiency in the body. Copper deficiency itself produces a phenotype that mimics B12 subacute combined degeneration. Myeloneuropathy with sensory ataxia and gait abnormality. Anemia, where the morphology is variable; it may be normocytic or macrocytic, and microcytic is the less common picture rather than the rule. And neutropenia. The mechanism for the anemia is that ceruloplasmin is required for iron mobilization from cells to transferrin, and copper deficiency disrupts that step, producing iron-restricted erythropoiesis. The neurologic mechanism is impaired cytochrome c oxidase activity in neurons. The diagnostic workup measures serum copper and ceruloplasmin, both of which are low in deficiency. The testable rule is that copper deficiency mimics B12 subacute combined degeneration, and the discriminator is that B12 levels are normal in copper deficiency. The other discriminator is the zinc history. A patient on chronic denture cream, on chronic zinc lozenges, or post-bariatric surgery with myeloneuropathy and a normal B12 is the copper-deficiency stem. Treatment is oral copper supplementation two milligrams daily, with concurrent reduction of any zinc source.

5:35Manganese is the inverse problem for parenteral nutrition. Dietary manganese deficiency essentially does not occur in humans because the requirement is small and dietary supply is ample. The testable entity is manganese toxicity from chronic parenteral nutrition. Manganese is normally excreted in bile, and cholestasis impairs that disposal route. The intravenous route also bypasses the gut barrier that normally limits manganese absorption. The result is accumulation in the basal ganglia, particularly the globus pallidus, with T1-weighted MRI hyperintensity and parkinsonian signs that may not respond to levodopa. Rigidity. Bradykinesia. Postural instability. Manganese is removed from parenteral nutrition formulations once cholestasis develops or once T1 signal change is detected.

6:24Selenium deficiency produces cardiomyopathy. The historical name is Keshan disease, after the deficient region of China where it was first described. The mechanism is that selenium is a cofactor for glutathione peroxidase, and its absence increases oxidative damage to the myocardium. Selenium deficiency can also produce thyroid dysfunction because deiodinase enzymes are selenoproteins. Deficiency in industrialized populations is rare but occurs in long-term unsupplemented parenteral nutrition. The recognition stem is a chronic-parenteral-nutrition patient with new heart failure and no other cause, particularly when the prescription was modified to omit the multitrace-element additive. The reverse problem is selenosis. Alopecia. Brittle nails with longitudinal streaks. Onycholysis. Garlic breath, from dimethyl selenide exhalation. Peripheral neuropathy. Gastrointestinal symptoms. The classic clinical context is Brazil nut overconsumption, more than three nuts per day chronically, because Brazil nuts concentrate selenium dramatically. A single nut can contain one hundred micrograms or more of selenium, several times the daily requirement. Treatment is reduction of selenium intake. Chromium deficiency on long-term chromium-free parenteral nutrition produces glucose intolerance because chromium is a cofactor in insulin signaling, and repletion restores normoglycemia.

7:44One last metabolic complication that the boards cluster with the trace elements. D-lactic acidosis in colon-retaining short bowel syndrome. Carbohydrate that escapes small-bowel absorption reaches the colon, where lactobacilli ferment it into both L-lactate and D-lactate. Human metabolism handles L-lactate but only slowly metabolizes D-lactate, which accumulates and produces neurologic symptoms with high anion-gap metabolic acidosis. Slurred speech. Ataxia. Confusion. The bedside clue is that the standard L-lactate is normal and the anion gap is unexplained until D-lactate is sent specifically. Treatment is carbohydrate restriction and oral antibiotics, metronidazole or neomycin, to suppress the lactobacilli population.

8:32Pull the mineral and trace-element threads together. Each element pairs a recognition cue with a population and a replacement, the same teaching unit as the vitamins. Iron deficiency frames chronic GI blood loss and the malabsorptive anatomies. PPI-induced hypomagnesemia is the long-term PPI user with tetany and the kinetic asymmetry between discontinuation and rechallenge. Zinc is acrodermatitis with altered taste in short bowel, Crohn, alcohol, and post-bariatric. Copper is myeloneuropathy with variable-morphology anemia and neutropenia, mimicking B12 subacute combined degeneration but with B12 normal, especially after chronic zinc excess from denture cream or supplements. Selenium is Keshan cardiomyopathy in chronic parenteral nutrition, with Brazil nut selenosis as the toxicity mirror. And manganese and chromium are the parenteral-nutrition problems, manganese accumulating in the globus pallidus under cholestasis and chromium deficiency producing glucose intolerance.

9:36The next chapter shifts from nutrition to infection. Chapter thirty three is GI Infections. C. difficile diagnosis and severity stratification with fidaxomicin as first-line therapy. Recurrent C. diff treated with bezlotoxumab and live biotherapeutics like Rebyota and Vowst. Travelers' diarrhea and bacterial enterocolitis. Parasitic and viral diarrheal infections. And the immunocompromised-host syndromes with CMV colitis and MAC and Cyclospora.

10:12For the full chapter, the practice vignettes, and the topic-tagged question bank, head to board pearls dot com. You'll find the rest of the series on Apple Podcasts, Spotify, or wherever you listen to podcasts. That brings us to the end of episode four of four of chapter thirty two, and I'll see you in the next one.