Vitamin deficiencies and toxicities
Vitamin deficiency and toxicity syndromes cluster into fat-soluble (A, D, E, K) and water-soluble (B1, B3, B6, B9, B12, C) patterns that arise mainly from malabsorption, bariatric surgery, alcohol use, or restricted diets. Recognizing the clinical syndrome and confirming it with the specific vitamin level allows targeted repletion, while excess supplementation drives the mirror-image toxicity syndromes.
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What this article covers
- Overview
Scope: two families, fat-soluble (A, D, E, K), absorbed with dietary fat and stored in liver/fat, and water-soluble (B1 thiamine, B3 niacin, B6 pyridoxine, B9 folate, B12 cobalamin, C ascorbic acid)…
- Epidemiology
Malabsorptive surgery and disease drive most adult cases: bariatric surgery, celiac disease, and ileal IBD (bariatric surgery, celiac disease, inflammatory bowel disease).
- Risk factors
Malabsorptive bariatric surgery: Roux-en-Y bypass and biliopancreatic diversion reduce B12 and fat-soluble vitamin uptake; banding carries lower risk.
- Pathophysiology
Fat-soluble absorption requires micellar solubilization with bile acids, so reduced bile delivery, pancreatic lipase, or absorptive surface reduces A, D, E, and K together.
- Clinical features
Vitamin A: deficiency causes night blindness first, then xerophthalmia and Bitot spots; toxicity causes headache/papilledema from intracranial hypertension, classically an obese young woman with…
- Differential diagnosis
Iron deficiency anemia: microcytic, not macrocytic, with low ferritin.
- Diagnosis
Recognize the syndrome clinically, then confirm with the vitamin level or functional marker.
- Management
First, treat suspected thiamine deficiency before any glucose is given, the one time-critical step: thiamine 500 mg IV every 8 hours for 2-3 days, then 250 mg IV/IM once daily for 3-5 more days if…
- Complications
Irreversible neurologic injury: Korsakoff syndrome reverses in only about 20% of patients despite thiamine repletion; delayed B12 treatment can leave permanent deficits.
- Prognosis
Most water-soluble deficiencies respond rapidly and completely when treatment starts before irreversible damage.
- Prevention
Universal newborn vitamin K prophylaxis: phytonadione 0.5-1 mg IM once within 1 hour of birth.
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- Celiac disease
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- Pernicious anemia
Pernicious anemia is autoimmune atrophic gastritis that destroys gastric parietal cells and abolishes intrinsic factor production, causing vitamin B12 malabsorption, megaloblastic macrocytic anemia, and a potentially irreversible myelopathy and neuropathy. Diagnosis rests on a low or borderline B12 with an elevated methylmalonic acid, confirmed by anti-intrinsic factor antibody, and treatment is lifelong vitamin B12 replacement.
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Hypercalcemia is an elevated serum calcium concentration, most often caused by primary hyperparathyroidism in ambulatory patients or malignancy in hospitalized patients. Mild disease requires only treatment of the underlying cause, while severe or symptomatic hypercalcemia is treated with aggressive IV isotonic fluids, followed by an IV bisphosphonate or denosumab for sustained control and subcutaneous calcitonin as a rapid but short-lived bridge.