A 33 year old woman presented to the ER with general weakness.

Explanation

Core Concept: Vitamin D is a fat-soluble vitamin essential for intestinal calcium absorption and bone mineralization. While the skin synthesizes Vitamin D upon exposure to UVB sunlight, dietary sources are crucial, especially in deficient individuals. Fish liver oils (such as cod liver oil), fatty fish (salmon, mackerel, sardines), and fortified foods are the richest natural dietary sources of Vitamin D.

Clinical Presentation:

• Vitamin D deficiency in adults causes osteomalacia (softening of bones), presenting as diffuse bone and joint pain, proximal muscle weakness, and fatigue.
• In children, severe deficiency causes rickets (bowed legs, delayed growth, craniotabes).
• Complications include osteoporosis, increased risk of fragility fractures, and secondary hyperparathyroidism.

Diagnosis:

• First-line diagnostic tool: Clinical assessment of risk factors (lack of sun exposure, malabsorption syndromes, dark skin pigmentation) and physical symptoms.
• Gold standard diagnostic test: Serum 25-hydroxyvitamin D [25(OH)D] level testing, with levels < 20 ng/mL generally indicating deficiency.

Management:

• Acute management: High-dose oral Vitamin D supplementation (e.g., ergocalciferol or cholecalciferol 50,000 IU weekly for 8 weeks) to rapidly replenish depleted body stores.
• Gold standard long-term/definitive management: Maintenance daily Vitamin D supplementation (e.g., 800-2000 IU/day), adequate dietary calcium intake, and safe, moderate sun exposure.