Is a Single 600,000 IU Dose of Vitamin D Safe?
A single stat dose of 600,000 IU (6 lakh) vitamin D should NOT be given as a bolus, as this approach has been shown to be inefficient and potentially harmful. 1, 2
Why Single Mega-Doses Are Problematic
Single annual mega-doses of 500,000-540,000 IU have been associated with adverse outcomes including increased falls and fractures in clinical trials, and the VIOLET trial demonstrated that ultra-high loading doses (540,000 IU) given without maintenance dosing were ineffective. 1, 2
The ESPEN guidelines explicitly state that bolus doses with longer dosing intervals than a week may be inefficient or even harmful, and daily or weekly vitamin D supplementation shows superior protective effects compared to large single doses, especially for preventing respiratory infections. 1
Single large doses of 300,000-500,000 IU should be avoided according to research evidence on vitamin D supplementation safety. 3
The Correct Approach to Severe Deficiency
For severe vitamin D deficiency requiring rapid correction, the evidence supports administering a cumulative dose of at least 600,000 IU, but this must be divided over several weeks, not given as a single bolus. 2, 3
Recommended Loading Regimens:
50,000 IU weekly for 8-12 weeks (total 400,000-600,000 IU over 2-3 months), followed by maintenance therapy of 1,500-2,000 IU daily. 2, 4
Alternatively, 2,000 IU daily for 12 weeks can be used for documented deficiency in children, with adult equivalents being proportionally higher. 4
For recurrent deficiency, 4,000-5,000 IU daily for 2 months targeting serum 25(OH)D levels of 40-60 ng/mL. 1, 2
Safety Thresholds and Toxicity Risk
Vitamin D toxicity is rare but serious, occurring with true overdoses and causing hypercalcemia, hypercalciuria, dizziness, and renal failure. 1, 5
The upper safety limit for serum 25(OH)D is 100 ng/mL, with toxicity typically occurring at levels >150 ng/mL (>375 nmol/L). 1, 5
Daily doses up to 4,000 IU are generally safe, with some authorities considering up to 10,000 IU daily safe for several months in at-risk patients. 5, 6
A single 600,000 IU dose could theoretically raise serum 25(OH)D by approximately 600 ng/mL based on the rule of thumb that 1,000 IU raises levels by ~10 ng/mL, though individual responses vary significantly. 2
Critical Monitoring Requirements
Measure baseline 25(OH)D, calcium, phosphorus, alkaline phosphatase, and PTH before initiating any high-dose therapy. 4
Recheck 25(OH)D levels 3 months after starting supplementation to assess response and ensure levels are in the target range of 30-80 ng/mL without exceeding 100 ng/mL. 2, 4
Monitor serum and urinary calcium during high-dose therapy, as hypercalcemia and hypercalciuria can occur even without developing hypervitaminosis D. 1, 7
Common Pitfalls to Avoid
Do not confuse vitamin D units: A dispensing error giving 50,000 IU daily instead of 1,000 IU daily has caused documented hypervitaminosis D with hypercalcemia and acute kidney injury. 8
Use vitamin D3 (cholecalciferol) rather than D2 (ergocalciferol), as D3 maintains serum levels longer and has superior bioavailability for intermittent dosing. 2, 4
Ensure adequate calcium intake (1,000-1,200 mg daily) during vitamin D treatment, as vitamin D enhances calcium absorption and adequate dietary calcium is necessary for clinical response. 1, 4, 9
Avoid using active vitamin D analogs (calcitriol) to treat nutritional vitamin D deficiency; reserve these for specific conditions like CKD stages 4-5. 4