["Abnormal Liver Function Tests","Acne vulgaris","Acute Bronchitis","Acute Kidney Injury","Adrenal Insufficiency","Allergic Rhinitis","Anemia","Approach to Abdominal Pain","Approach to Acid Base Disorders","Approach to Bone Loss","Approach to Bright Red Blood Per Rectum (BRBPR)","Approach to Cervical cancer screening","Approach to Chest Pain","Approach to Constipation","Approach to Cough","Approach to Dementia","Approach to Diarrhea","Approach to Dizziness","Approach to Dysphagia and Odynophagia","Approach to EKG","Approach to Falls","Approach to Fatigue","Approach to Fever","Approach to Hematuria","Approach to Hemoptysis","Approach to Hypercoagulable Disorders","Approach to Hyperkalemia","Approach to Hypernatremia","Approach to Hyperprolactinemia","Approach to Hypocalcemia","Approach to Hypoglycemia","Approach to Hypokalemia","Approach to Hyponatremia","Approach to Hypothyroidism","Approach to Jaundice","Approach to Low Back Pain","Approach to Muscle weakness","Approach to Nausea and Vomiting","Approach to Neck Pain","Approach to Palpitations","Approach to Peripheral Edema","Approach to Proteinuria","Approach to Seizure","Approach to Shortness of Breath (Dyspnea)","Approach to Splenomegaly","Approach to Syncope","Approach to Thyroid Nodule","Approach to Unintentional Weight Loss","Asthma","Bell\u2019s Palsy","Benign Prostatic Hyperplasia (BPH)","Bleeding Disorders","Breast cancer screening","Bronchiectasis","Celiac disease","Chronic Kidney Disease","Chronic Obstructive Pulmonary Disease (COPD)","Cirrhosis","Colon cancer screening","Congestive Heart Failure (CHF)","Crohn\u2019s Disease","Cushing\u2019s Syndrome","Delirium","Depression","Diabetes Insipidus","Diverticulosis and Diverticulitis","Dyspepsia","Gastroesophageal Reflux Disease (GERD)","Generalized Anxiety Disorder (GAD)","Headache","Hearing loss","Helicobacter pylori (H. pylori)","Hemorrhoids","Hepatitis B","Hepatitis C","Hypercalcemia","Hypertension","Irritable Bowel Syndrome (IBS)","Kidney stones","Leukocytosis","Leukopenia","Lipid Disorders","Lymphadenopathy","Meningitis and Encephalitis","Microscopic Colitis","Obstructive Sleep Apnea","Pancreatitis","Peptic Ulcer Disease (PUD)","Pericardial Disease","Pneumonia","Stroke and TIA","Ulcerative Colitis","Upper Gastrointestinal Bleeding","Urinary Dysfunction","Urinary Tract Infection (UTI)","Vitamin D deficiency"]

Vitamin D deficiency

Background and metabolism of vitamin D

Vitamin D deficiency

Type	Clinical features
Sources of Vitamin D	Dermal synthesis Previtamin D3 synthesized nonenzymatically in skin from dehydrocholesterol after UV sunlight exposure Previtamin D3 converted to vitamin D3 (cholecalciferol) Darker skin has more melanin, which can decrease D3 production Dietary intake Fortified dairy products Fatty fish liver Cod liver
Metabolism of Vitamin D	*Dietary absorption* Vitamin D (fat soluble) absorbed by enterocytes into chylomicrons Disorders decreasing dietary vitamin D3 absorption Celiac disease Crohn disease Cystic fibrosis Short gut syndrome Pancreatic insufficiency *Metabolism* Both dietary and synthesized vitamin D converted in liver to 25-hydroxyvitamin D (25-OHD, calcidiol) Kidney converts 25-OHD to 1,25- dihydroxyvitamin D (1.25-OH2D) (calcitriol) Active form with shorter half-life than 25-OHD Renal activation regulated by PTH, serum calcium, and serum phosphate concentrations *Recommended intake* 800-2000 IU/day depending on patient’s risk factors for deficiency Measuring 25-OHD is best laboratory marker of vitamin D adequacy

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