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home - Nutrition - Vitamins - Vitamin D Written by Dr Sebastian Zeki

Vitamin D

Protein D Micelles D Pancreatic enzymes Bile acids Absorption into entero-cyte in distal small bowel Packaged into chylomicrons 25-vitamin-D hydroxylase 25-hydroxy-vitamin-D (25OHD) 1,25-dihydroxy-vitamin D (1,25(OH)2-vitamin D) This is the physiologically active form Vitamin D PTH + Enhances intestinal absorption of calcium Bone OestrogenPlacental growth hormoneProlactin May also regulate vitamin D metabolism ExcessHypercalcaemia (usually if >60,000U/ day).Maximum tolerated daily dose is <2000IU. Glucocorticoids, when used chronically in high doses, inhibit the intestinal vitamin D dependent calcium absorption and therefore cause osteomalacia Causes of Deficiency DeficiencyEarly in hypovitaminosis D, hypophos-phatemia is more marked than hypocalcae-mia.With persistent hypovitaminosis D, hypocalcemia causes a secondary hyperpar-athyroidism that leads to phosphaturia, demineralization of bones, and, without treatment, to osteomalacia in adults and rickets in children. Liver damage (unable to hydroxylate Kidney damage End organ insensitivity to vit D Action of Vitamin D Requirements of vitamin D —RDA: 800 IU/ dIf low give 50,000 units vitamin D2 (ergocalciferol 2-3x/wk until normal levels25-OH vitamin D is best serum measure- need minimum level of 30 ng/ml (75 nmol/L) Serum PTH is inversely related to 25-OH vitamin D Provitamin D Vitamin D3 Sunlight bound to Vitamin D binding proteins (DBP) Blood Skin Diet Fortified milk, bread and cerealFatty fishCod-liver oilEggs.             Vitamin D Sources Mechanism of absorption Investigation and treatment of Vitamin D Deficiency Vitamin D symptoms present?-Widespread bone pain/ tenderness or myalgiaProximal muscle weaknessTenderness over pseudofracturesInsufficiency fractures Does the patient have >1 risk factor for vitamin D deficiency?Black/ ethnic minorityElderly and houseboundHabitual skin coveringVegan/ vegetarianLiver/ renal diseaseMalabsorptionAnticonvulsants/ cholestyramine/ rifampicin/ anti-retrovirals Vitmain D tests: 25(OH)D,Ca2+,PTH,ALP,PO4 Deficiency <25nmol/L1st line: Colecalciferol 20,000U capsule: Take 3 caps ow for 12 weeks2nd line: Colecalciferol 300,000U IM injection.One immediately then repeat at 12 weeks3rd line: 300,000U in 100ml colecalciferol liquid: Take 50ml od for 2 days Insufficiency 25-50nmol/LColecalciferol 1,000U tablet:Take 1-2 taletsod for 12 weeks Sufficient >50nmol/LLifestyle and dietary advice Repeat levels at 12 weeks. Monitor patient every 12 monthsConsider maintenance if ongoing risk1st line: cacium carbonate 1.5g & colecalciferol 400U chewable tablet: 1 tablet bd2nd line: Colecalciferol 1,000U tablet: od (only if adequate ca intale or at risk of hypercalcaemia) AND Treatment based on serum 25-OH D level If still insufficient then refer for specialist advice

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