1 / 40

Calcium & Vitamin D Physiology

Calcium & Vitamin D Physiology. Bob Bing-You, MD, MEd, MBA ME Center for Endocrinology Scarborough, Maine. Importance of Calcium. Tight physiologic range Normal function muscle, nerves, PLTs, coagulation factor Cofactor for enzymes Membrane stability So we can stay upright!.

Download Presentation

Calcium & Vitamin D Physiology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Calcium & Vitamin D Physiology Bob Bing-You, MD, MEd, MBA ME Center for Endocrinology Scarborough, Maine

  2. Importance of Calcium • Tight physiologic range • Normal function muscle, nerves, PLTs, coagulation factor • Cofactor for enzymes • Membrane stability • So we can stay upright!

  3. Calcium balance • Net intestinal Ca absorption ~zero when intake <200 mg/d • need >400 mg/d to maintain Ca balance • >1000 mg/d, intestinal absorption tends to plateau

  4. Calcium absorption • 1,25-OH vitamin D [calcitriol] only hormonal stimulus for active absorption • acts primarily on duodenum, jejunum • fairly linear increase in Ca absorption with increasing calcitriol levels

  5. The following statement is true: • A. You can get enough vitamin D through a window • B. Osteoblasts are the “PAC-men meanies” • C. 1,25-D is better than 25-D for Ca absorption • D. Serum Ca reflects most of our Ca stores

  6. History of vitamin D • Century-old documents described Vit D disease • Rickets in industrial England • 1919- rickets produced in dogs fed oatmeal indoors, cured with cod-liver oil • 1923- skin precursor identified • 1930’s – chemistry determined

  7. Normal vitamin D internal production • Skin: Vit D3 [cholecalciferol], made by ultraviolet light [can’t get it through windows!] • Liver: 25-hydroxy Vit D • Kidney: 1,25-dihydroxy Vit D [calcitriol] =active form which acts on intestines • Stimulated by parathyroid hormone

  8. Vitamin D deficiency • Osteomalacia [bone without calcium] • Parathyroid glands come to defense at sacrifice of bones • Risk of fractures • Cancer risk?

  9. How does one get deficient? • Winter months [Boston Univ. studies: Nov – Feb] • Age related changes: Skin does not convert Vit D3; less intestinal absorption • Sun screen • Liver or kidney disease

  10. How much sunlight do you need? • A. None, too dangerous • B. One hour a week • C. 20 minutes 4 days a week • D. One hour a day

  11. Dietary sources of vitamin D • Egg yolks • Fatty fish like salmon • Fatty fish oils like cod liver oil • Supplemented foods [milk 400IU/Liter, cereals, breads] • Typical adult diet <100 IU

  12. How do we detect deficiency? • 25-hydroxy Vit D level • Reflects nutritional stores over months • 1,25 Vit D expensive and short-lived • normal level, probably > 30 ng/ml • This level quiets down parathyroids

  13. Medical conditions • Hypoparathyroidism • Chronic renal failure • Intestinal osteodystrophy [e.g., celiac sprue, gastric bypass]

  14. Supplements suggested • DRI [Dietary Reference Intake]: minimum amount to prevent diseases from deficiency • Not for optimal health • International Units [40 IU Vit D = 1 microgram] • 400 IU?, 800?, 1000? • >2000 IU – should be monitored

  15. Vitamin D preparations • Calcitriol [1,25 vit-D] • Rocaltrol 0.25 to 0.5 mcg per day • Calcijex parenteral 1-2 mcg/ml • Calcifediol [25- vit D] • less effective in gut Ca absorption, less hypercalcemia risk

  16. Too much is possible! • Stays in fat tissue long time • Increases calcium loss from bone • Premature heart attacks • High blood levels, kidney stones • Too much sun doesn’t cause Vit D toxicity • Watch out for Vitamin A combo [some tablets are cod liver oil, with both A & D]

  17. Causes Hypocalcemia • Is it truly low? Mental calculation to correct results Ca upwards for low albumin [about 1 to 1] b/c serum total Ca measures bound Ca to albumin • or measure ionized Ca [“free” amount]’ ?reliable test • Vitamin D deficiency • Hypoparathyroidism • surgery • functional [Mg] • Alkalosis

  18. Assuming a normal albumin is 4: if your patient has a total Ca reported at 7.0, & with an albumin of 2, what would be the corrected Ca [mentally calculate it]: • A. 5.0 • B. 7.0 • C. 9.0 • D. 10.0 • E. I need a calculator

  19. Hypocalcemia - signs/sx’s • Paraesthesias • tetany, carpopedal spasm, muscle cramps • Chvostek’s sign • Trousseau’s sign • Prolonged QT • seizures of all types • Laryngospasm, bronchospasm

  20. Hypocalcemia - treatment • Any symptomatic patient, or asymptomatic with Ca <7.5 • Ca gluconate 10 ml [90 mg] IV in 50 ml D5W or NS, over 5 minutes • repeat injections or go with infusion [10 ampules in 1 liter @ 50 ml/hr] • start vitamin D if prolonged course expected; replace Mg if necessary

  21. Calcium • Carbonate [40% elemental Ca] • Lactate [13%] • Phosphate [25%] • Citrate [17%] • Gluconate best for IV- least irritating

  22. Calcium • Carbonate [TUMS]: low cost, antacid properties, highest Ca % • Constipation • 1000 - 1500 mg/ day • achlorhydric pts should take with food • IV infusions: watch Ca x Phos product

  23. Causes hypercalcemia • Outpatient- primary hyperparathyroidism • Inpatient - malignancy • Less common • pheochromocytoma • meds: lithium, thiazides, vit D • hyperthyroidism • TB, sarcoid, • critical illness

  24. Parathyroid • Needed to facilitate 1,25 hydroxylation • calcium sensing receptor • negative feedback loop • 1-84 amino acids, N-terminal active component

  25. Hyperparathyroidism • Secondary - due to low serum Ca • Primary - due to single adenoma • Mulitple Endocrine Neoplasia syndrome • surgery: bone loss, kidney stones, serum Ca >11.5 mg% • Medical Rx: receptor blocker [Cinacalcet]

  26. Hypercalcemia - signs/sx’s • Lethargy, stupor, coma • mental status changes • N/V, constipation • HTN, short QT, AV block • weakness, bone pain • stones, fractures

  27. Hypercalcemia - treatment • Hydration • Furosemide • bisphosphonates [zoledronic acid, pamidronate, etidronate] • calcitonin • steroids for hematologic malignancies • dialysis for renal patients; watch Ca x Phos

  28. Take-home points • Calcium balance important for normal physiologic functions • we all need vitamin D! • hypocalcemia life-threatening • hypercalcemia either PHT or malignancy

  29. Websites • www.uwcme.org/courses/bonephy [Dr Susan Ott] • www.osteoporosis.ca [Osteoporosis Society of Canada] • www.aad.org [Acad of Dermatology] • www.vitamin-d.com, www.nutritionfarm.com, www.merck.com

More Related