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Vitamin D
Vitamin D is a fat-soluble vitamin essential for bone health, immune function, and overall well-being. Unlike other vitamins, it can be synthesized by the skin through sunlight exposure. However, deficiencies are common globally, necessitating dietary or supplemental intake. This article synthesizes information from authoritative sources, including the British National Formulary (BNF), Lippincott Textbook of Pharmacology, Lange Basic & Clinical Pharmacology, Mayo Clinic, and Harvard Medical School, to provide a detailed overview of vitamin D.
- Bone Health:
- Facilitates calcium absorption, preventing rickets in children and osteomalacia/osteoporosis in adults (Mayo Clinic).
- Immune Support:
- Modulates immune responses, reducing infection risk and inflammation (Harvard Medical School).
- Muscle Function:
- Maintains muscle strength, reducing fall risk in the elderly (BNF).
- Mental Health:
- Emerging evidence links adequate levels to reduced depression risk (Lange).
- Chronic Disease Prevention:
- Associated with lower risks of cardiovascular disease, diabetes, and certain cancers (Harvard Medical School).
- Sunlight:
- 10–30 minutes of midday sun exposure (without sunscreen) several times weekly (Mayo Clinic).
- Food Sources:
- Fatty fish (salmon, mackerel), egg yolks, fortified dairy/milk alternatives, and mushrooms (UV-exposed).
- Supplements:
- Available as D2 or D3 in tablets, capsules, drops, or injections (BNF).
Deficiency is often asymptomatic but may manifest as:
- Musculoskeletal: Bone pain, muscle weakness, fractures.
- Developmental: Rickets (bowed legs, stunted growth in children).
- Fatigue and Mood Changes: Lethargy, depression (Lange).
- Frequent Infections: Impaired immune function (Harvard Medical School).
Risk Factors:
- Limited sun exposure, darker skin pigmentation, obesity, malabsorption disorders (e.g., Crohn’s), aging, and strict veganism.
- Normal: 20–50 ng/mL (Mayo Clinic).
- Insufficiency: 12–20 ng/mL.
- Deficiency: <12 ng/mL.
- Toxicity: >150 ng/mL (rare, from excessive supplementation).
- Vitamin D3 (Cholecalciferol):
- OTC Tablets: 400 IU, 1000 IU, 2000 IU, 5000 IU.
- Prescription: High-dose formulations (e.g., 50,000 IU weekly for deficiency).
- Vitamin D2 (Ergocalciferol):
- Less potent; used in vegan supplements and prescriptions.
- Combination Formulas:
- Often paired with calcium (e.g., Caltrate®).
- Deficiency Treatment:
- Corrects low levels to prevent bone disorders (BNF).
- Osteoporosis Management:
- Combined with calcium to reduce fracture risk (Lippincott).
- Chronic Kidney Disease:
- Supports calcium-phosphate balance (Lange).
- Autoimmune Conditions:
- Adjunctive therapy for multiple sclerosis and rheumatoid arthritis (Harvard Medical School).
Daily Requirements (IU):
- Infants: 400–1,000.
- Adults: 600–800.
- Pregnancy/Elderly: 800–2,000 (Mayo Clinic).
Deficiency Correction:
- Adults: 50,000 IU D2/D3 weekly for 6–8 weeks, then 1,500–2,000 IU daily (BNF).
Administration Tips:
- Take with fatty meals to enhance absorption.
- Monitor serum levels every 3–6 months during treatment.
Vitamin D is safe at recommended doses but may cause:
- Mild: Nausea, constipation, dry mouth.
- Severe (Toxicity): Hypercalcemia (confusion, kidney stones, arrhythmias) (Lippincott).
- Hypercalcemia: Avoid in patients with high calcium levels.
- Kidney Disease: Monitor calcium and phosphate closely.
- Sarcoidosis/Granulomatous Disorders: Risk of hypercalcemia (BNF).
- Pregnancy: Safe up to 4,000 IU/day; avoid megadoses (Mayo Clinic).
- Corticosteroids: Reduce vitamin D efficacy.
- Thiazide Diuretics: Increase hypercalcemia risk.
- Weight-Loss Drugs (Orlistat): Impair absorption.
- Anticonvulsants (Phenobarbital): Accelerate vitamin D metabolism (Lange).
- Vitamin D2: Ergocalciferol (Drisdol®).
- Vitamin D3: Cholecalciferol (Decara®), Calcitriol (for renal failure).
