Vitamin D Course

Lesson 1 • What Vitamin D Actually Is

Defines vitamin D2 and D3, their structural differences, and why classification as a vitamin is debated. Sets the conceptual baseline for all subsequent metabolism content.

Lesson 2 • Storage and Baseline Physiology

Covers adipose and muscle tissue storage, half-life, and baseline physiological concentrations. Prepares students to interpret serum measurement data introduced in later chapters.

Lesson 3 • Dietary and Sunlight Sources

Identifies natural food sources, fortified foods, and UVB-driven cutaneous synthesis. Connects source variability to the widespread deficiency problem addressed later.

Lesson 1 • Hepatic First Hydroxylation

Details the liver CYP2R1 and CYP27A1 enzymes converting vitamin D to 25-hydroxyvitamin D. Establishes 25(OH)D as the primary circulating and measurable metabolite.

Lesson 2 • Renal Second Hydroxylation

Explains CYP27B1-mediated conversion of 25(OH)D to calcitriol in the kidney. Links renal function to active hormone availability, critical for understanding deficiency in kidney disease.

Lesson 3 • Catabolism and Excretion Pathways

Covers CYP24A1-mediated inactivation and biliary excretion routes. Explains how catabolism prevents toxicity and how certain drugs accelerate degradation.

Lesson 4 • Feedback Regulation of Metabolism

Describes the hormonal feedback loop involving PTH, FGF23, calcium, and phosphate that governs calcitriol production. Provides the regulatory framework needed for clinical interpretation.

Lesson 1 • Rapid Non-Genomic Signaling

Covers membrane-associated receptor actions producing rapid second-messenger responses. Distinguishes these fast effects from slower genomic pathways covered in the previous section.

Lesson 2 • Key Target Genes and Their Functions

Catalogs major VDR-regulated genes in calcium transport, immune function, and cell cycle control. Provides the molecular evidence base for vitamin D's diverse physiological roles.

Lesson 3 • Genomic Signaling Mechanism

Traces calcitriol-VDR complex binding to vitamin D response elements and coactivator recruitment. Connects receptor activation to measurable changes in target gene expression.

Lesson 1 • Bone Mineralization and Remodeling

Covers osteoblast and osteoclast regulation by vitamin D and PTH in the bone remodeling cycle. Explains how adequate vitamin D ensures proper matrix mineralization.

Lesson 2 • Vitamin D and Osteoporosis Risk

Differentiates osteomalacia from osteoporosis and evaluates vitamin D's role in fracture prevention. Prepares students for supplementation dosing discussions in later chapters.

Lesson 3 • Deficiency Skeletal Diseases

Distinguishes rickets in children from osteomalacia in adults, including clinical presentation and radiographic findings. Connects biochemical deficiency to structural bone pathology.

Lesson 4 • Intestinal Calcium Absorption Mechanisms

Details transcellular and paracellular calcium transport in the small intestine regulated by calcitriol. Quantifies the absorption efficiency difference between sufficient and deficient states.

Lesson 1 • Choosing the Right Biomarker

Justifies 25(OH)D over calcitriol as the preferred status marker based on half-life and stability. Clarifies why calcitriol levels can be normal or elevated even during deficiency.

Lesson 2 • Laboratory Assay Methods

Compares immunoassay, HPLC, and LC-MS/MS methods for measuring 25(OH)D. Explains inter-assay variability and standardisation efforts affecting result interpretation.

Lesson 3 • Screening Indications and Frequency

Defines clinical scenarios warranting targeted versus universal screening and appropriate retesting intervals. Connects testing strategy to cost-effective deficiency management.

Lesson 4 • Factors Affecting Serum Levels

Catalogues biological, behavioural, and environmental variables that influence measured 25(OH)D. Enables accurate interpretation of results in diverse patient populations.

Lesson 1 • Metabolic and Genetic Disorders

Describes hereditary disorders of vitamin D metabolism including vitamin D-dependent rickets types I and II. Explains how genetic variants in CYP and VDR genes alter status.

Lesson 2 • Drug-Induced Deficiency

Lists drug classes that accelerate catabolism or impair absorption, including anticonvulsants, glucocorticoids, and antiretrovirals. Prepares students for pharmacological management decisions.

Lesson 3 • High-Risk Population Profiles

Synthesises risk factors into profiles for infants, elderly, pregnant women, and dark-skinned individuals. Enables targeted screening and prevention strategies covered in later chapters.

Lesson 4 • Dietary Insufficiency and Malabsorption

Covers low dietary intake, fat malabsorption syndromes, and bariatric surgery as deficiency drivers. Links gastrointestinal pathology to impaired vitamin D absorption.

Lesson 1 • Toxicity, Upper Limits, and Safety

Defines hypervitaminosis D, its biochemical markers, and the tolerable upper intake level evidence base. Distinguishes true toxicity from hypercalcaemia of other causes.

Lesson 2 • Maintenance Dosing by Population

Specifies evidence-based maintenance doses for infants, children, adults, elderly, and pregnant women. Connects population-specific physiology from Chapter 6 to practical dosing decisions.

Lesson 3 • Supplement Forms and Bioavailability

Compares D2 and D3 supplement forms, oil-based versus dry formulations, and calcifediol for special populations. Guides form selection based on patient-specific absorption capacity.

Lesson 4 • Dosing Strategies for Deficiency Correction

Presents loading dose protocols, maintenance dosing, and dose-response relationships for correcting deficiency. Provides calculation frameworks applicable across age groups.

Lesson 1 • Neurological and Mental Health Associations

Summarises evidence linking vitamin D to cognitive decline, depression, and neurodevelopmental outcomes. Applies critical appraisal skills to distinguish correlation from causation.

Lesson 2 • Cardiovascular and Metabolic Health

Reviews observational and interventional evidence for vitamin D in blood pressure, insulin sensitivity, and cardiovascular risk. Distinguishes confounded associations from causal evidence.

Lesson 3 • Cancer Biology and Prevention

Covers VDR-mediated antiproliferative, pro-apoptotic, and anti-angiogenic mechanisms relevant to cancer. Evaluates randomised trial evidence for supplementation in cancer incidence and mortality.

Lesson 4 • Immune System Modulation

Explains calcitriol's role in innate and adaptive immunity, including cathelicidin induction and T-cell regulation. Evaluates evidence for vitamin D in respiratory infection and autoimmune disease.