Download The Missing Vitamin: Vitamin D

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!
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
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
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
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
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
Vitamin D deficiency
Osteomalacia [bone without calcium]
Parathyroid glands come to defense at
sacrifice of bones
Risk of fractures
Cancer risk?
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
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
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
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
Medical conditions
Hypoparathyroidism
Chronic renal failure
Intestinal osteodystrophy [e.g., celiac
sprue, gastric bypass]
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
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
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]
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
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
Hypocalcemia - signs/sx’s
Paraesthesias
tetany, carpopedal spasm, muscle cramps
Chvostek’s sign
Trousseau’s sign
Prolonged QT
seizures of all types
Laryngospasm, bronchospasm
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
Calcium
Carbonate [40% elemental Ca]
Lactate [13%]
Phosphate [25%]
Citrate [17%]
Gluconate best for IV- least irritating
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
Causes hypercalcemia
Outpatient- primary hyperparathyroidism
Inpatient - malignancy
Less common
–
–
–
–
–
pheochromocytoma
meds: lithium, thiazides, vit D
hyperthyroidism
TB, sarcoid,
critical illness
Parathyroid
Needed to facilitate 1,25 hydroxylation
calcium sensing receptor
negative feedback loop
1-84 amino acids, N-terminal active
component
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]
Hypercalcemia - signs/sx’s
Lethargy, stupor, coma
mental status changes
N/V, constipation
HTN, short QT, AV block
weakness, bone pain
stones, fractures
Hypercalcemia - treatment
Hydration
Furosemide
bisphosphonates [zoledronic acid,
pamidronate, etidronate]
calcitonin
steroids for hematologic malignancies
dialysis for renal patients; watch Ca x Phos
Take-home points
Calcium balance important for normal
physiologic functions
we all need vitamin D!
hypocalcemia life-threatening
hypercalcemia either PHT or malignancy
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