Vitamin D
Dosage and interpretation of 25-OH-D levels
- Severe deficiency (<25 nmol/L or <10 ng/mL): rickets (child) + osteomalacia (adult) + symptomatic hypocalcemia + proximal myopathy + tetany → urgent intensive supplementation
- Insufficiency (25–50 nmol/L or 10–20 ng/mL): Reactive secondary hyperparathyroidism (high PTH → increased bone resorption) + risk of falls and fractures + supplementation necessary
- Optimal for bone health (50–125 nmol/L or 20–50 ng/mL): Recommended target by Osteoporosis Canada + Health Canada for the general population → maintenance supplementation according to dietary intake and sun exposure
- High target discussed (75–150 nmol/L or 30–60 ng/mL): recommended by some experts for at-risk populations (elderly + chronic diseases + malabsorption) → evidence is still insufficient to universally recommend this higher target
- Toxicity (>250 nmol/L or >100 ng/mL): Hypercalcemia + hypercalciuria + kidney stones + vascular calcifications + nausea + fatigue → only with doses >10,000 IU/day prolonged or with accidental poisoning + never with sun exposure alone (protective cutaneous regulation mechanism)
- Important Note — Units: nmol/L (Canada + Europe) vs ng/mL (United States) → conversion: nmol/L ÷ 2.5 = ng/mL (e.g., 50 nmol/L = 20 ng/mL)
Populations at risk of deficiency — Quebec
- All Quebecers in winter (November to March): latitude 45–50°N → insufficient solar angle for cutaneous synthesis + universal supplementation recommendation
- Elderly people (>65 years old): Reduced skin synthesis capacity by 75% % + reduced sun exposure + often poor diet + decreased intestinal absorption + frequent kidney failure (reduced 1α-hydroxylase)
- Dark-skinned people melanin filters UVB → reduced skin synthesis → 3 to 5 times longer exposure needed to reach the same rate
- Obesity sequestration of fat-soluble vitamin D in adipose tissue → reduced bioavailability → higher supplementation doses needed
- Fat malabsorption Crohn's disease + celiac disease + cystic fibrosis + bariatric surgery (gastric bypass ++) + chronic pancreatitis → strongly reduced absorption of fat-soluble vitamin D → high-dose supplementation + monitoring of levels
- Pregnancy and breastfeeding: increased needs (1,500–2,000 IU/day recommended) + low vitamin D breast milk → supplement breastfed infant from birth (400 IU/day — Health Canada)
- Drugs inducing vitamin D catabolism: Antiepileptics (phenytoin + carbamazepine + phenobarbital — CYP24A1 inducers) + rifampicin + long-term glucocorticoids + antiretrovirals
Supplementation - practical recommendations
| Population | Recommended dose | Remarks |
|---|---|---|
| Breastfed infant (0–12 months) | 400 IU/day (10 mcg/day) from birth | Breast milk low in vitamin D + risk of rickets → Health Canada recommendation + Canadian Paediatric Society |
| Child and adolescent (ages 1–18) | 600 IU/day (15 µg/day) — Recommended Nutritional Intake + supplementation if diet is insufficient | Increase to 1,000–2,000 IU/day if little sun exposure + dark skin + vegan diet |
| Adult <65 years | 600–1,000 IU/day in summer + 1,000–2,000 IU/day in winter (October to April in Quebec) | Cholecalciferol D3 preferred over ergocalciferol D2 (more effective at raising and maintaining 25-OH-D levels) + continuous supplementation recommended in Quebec |
| Adult >65 years old | 800–2,000 IU/day ongoing | Osteoporosis Canada recommends 800–2,000 IU/day + combine with calcium if dietary intake is insufficient + monitor 25-OH-D levels annually |
| Osteoporosis + fractures | 800–2,000 IU/day + calcium 1,000–1,200 mg/day (preferably from diet) | Target 75–125 nmol/L + dietary calcium preferred over calcium supplements (cardiovascular risk of calcium supplements debated) |
| Malabsorption + Bariatric Surgery | 3,000–6,000 IU/day + or high dose (50,000 IU/week) supervised | Monitoring of 25-OH-D levels every 3-6 months + D3 form + high doses necessary due to very reduced absorption |
| Correction of a documented deficiency | 50,000 IU/week × 8–12 weeks (D2 or D3) + then maintenance | Rapid correction protocol for severe deficiencies (<25 nmol/L) + 3-month follow-up testing |
Consult a doctor if diffuse bone pain, proximal muscle weakness, cramps, or symptomatic hypocalcemia (perioral paresthesias, carpopedal spasm, Chvostek's sign) appear—these signs may indicate severe vitamin D deficiency (osteomalacia) requiring urgent testing and intensive supplementation. For 25-OH vitamin D testing and prescription of appropriate supplementation, Clinique Omicron offers medical consultations at its service points in Quebec and via telemedicine. To book an appointment, visit cliniqueomicron.ca.
Consult at Clinique Omicron
Clinique Omicron's physicians and nurse practitioners (NPs) measure 25-OH vitamin D in at-risk populations (elderly + malabsorption + pregnancy + dark skin + anti-epileptic drugs), prescribe vitamin D3 (cholecalciferol) supplementation tailored to the patient's level and profile, monitor the effectiveness of correction with follow-up testing at 3 months, incorporate vitamin D into the overall management of osteoporosis, and educate patients on safe sun exposure. Consultations are available at several service locations in Quebec and via telemedicine. To book an appointment, visit cliniqueomicron.ca.
The content of this page is provided for informational purposes only and does not replace the advice of a doctor or endocrinologist. Routine vitamin D screening is not recommended in the general asymptomatic population; it is reserved for at-risk populations. Do not exceed 4,000 IU/day without medical supervision. Vitamin D toxicity (hypercalcemia) occurs only with prolonged very high doses, never with sun exposure alone.
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