What are the risks of taking a high dose of vitamin D (Vit D), such as 100,000 units weekly?

Risks of High-Dose Vitamin D (100,000 Units Weekly)

Taking 100,000 units of vitamin D weekly poses significant risk of toxicity, as this dose falls within the range documented to cause intoxication (daily doses of >10,000 or even 100,000 IU), and should be avoided in favor of daily or weekly dosing at much lower levels. 1

Primary Toxicity Mechanisms

Vitamin D toxicity manifests through calcium dysregulation, causing: 1

• Hypercalcemia (elevated blood calcium)
• Hypercalciuria (excessive calcium in urine)
• Hyperphosphatemia (elevated blood phosphorus)
• Acute kidney injury and renal failure 1, 2
• Dizziness, nausea, vomiting, muscle weakness 3
• Altered mental status and confusion 2, 4
• Kidney stones, polyuria, and polydipsia 3

Why 100,000 Units Weekly Is Problematic

Exceeds Safe Dosing Parameters

• The general upper daily limit is 4,000 IU for healthy adults, with up to 10,000 IU daily considered safe by the Endocrine Society for deficiency treatment 3
• Your weekly dose of 100,000 IU equals approximately 14,300 IU daily, which exceeds recommended safe limits 3
• Most international authorities consider 2,000 IU daily as absolutely safe 1, 3

Bolus Dosing Is Physiologically Inferior

• Single large bolus doses should be avoided as they carry specific risks compared to daily or weekly dosing at lower amounts 3
• The VIOLET trial demonstrated that ultra-high loading doses (540,000 IU single dose) were ineffective and potentially harmful 1
• Daily or weekly vitamin D at moderate doses shows strong protective effects, especially in severe deficiency, while infrequent massive doses do not 1

Critical Safety Thresholds

Blood Level Toxicity Range

• Hypercalcemia from vitamin D toxicity generally occurs when 25(OH)D levels exceed 100-150 ng/mL 1, 3
• The safe upper limit for serum 25(OH)D is 100 ng/mL 1, 3
• Optimal therapeutic range is 30-80 ng/mL 3, 5

Documented Toxicity Cases

True intoxication has been documented with: 1

• Single doses of millions of IU
• Daily doses of >10,000 or even 100,000 IU
• Manufacturing errors leading to unintended overdoses 2

Hidden Dangers: Toxicity Without Hypervitaminosis D

A critical pitfall: Prolonged consumption of vitamin D supplements may induce calcium and phosphorus dysregulation leading to tissue and organ damage even without developing measurably high vitamin D blood levels 6

• Hypercalcemia and hyperphosphatemia are initial signs of intoxication 6
• When these abnormalities become apparent, tissue/organ damage may have already begun 6
• This means you cannot rely solely on vitamin D levels to assess safety 6

Cardiovascular and Other Risks

Animal experiments demonstrate that moderate amounts of oral vitamin D over time can result in atherosclerosis, suggesting angiotoxicity from differences in how oral vitamin D is metabolized 7

Recommended Safe Alternatives

For Treating Deficiency

• 4,000-5,000 IU daily for 2 months is appropriate for recurrent deficiency 1
• For severe deficiency: 50,000 IU weekly for 8 weeks, then maintenance of 800-2,000 IU daily 5
• Monthly dosing of 60,000 IU (equivalent to ~2,000 IU daily) is acceptable 5

For Maintenance

• 800-2,000 IU daily is safe for long-term maintenance 3, 5
• Target serum 25(OH)D levels of 30-60 ng/mL 1

Monitoring Requirements

For doses above 4,000 IU daily: 3

• Check baseline 25(OH)D levels
• Monitor serum calcium, phosphorus, and creatinine 4
• Recheck 25(OH)D at least 3 months after starting supplementation 3, 5
• Monitor for symptoms of hypercalcemia 4

High-Risk Populations

Increased sensitivity to vitamin D toxicity occurs in: 1

• Patients with CYP24A1 loss of function mutations
• Idiopathic infantile hypercalcemia
• Those taking thiazide diuretics 8
• Individuals with liver disease 8

Clinical Cases of Toxicity

Real-world cases demonstrate severe consequences: 2, 4

• A 70-year-old woman taking 50,000 IU daily (due to dispensing error) developed confusion, slurred speech, unstable gait, hypercalcemia, and acute kidney injury within 3 months 2
• Patients receiving mega-doses developed nausea, vomiting, altered sensorium, pancreatitis, acute kidney injury, and weight loss 4
• Recovery required 5 months after discontinuation 2

Bottom Line

Your current dose of 100,000 units weekly should be reduced immediately. Switch to evidence-based dosing: either 50,000 IU weekly for 8 weeks if treating documented deficiency (followed by 800-2,000 IU daily maintenance), or simply start with 2,000-4,000 IU daily if deficiency status is unknown. 1, 3, 5 Have your healthcare provider check baseline calcium, phosphorus, creatinine, and 25(OH)D levels before continuing any supplementation. 3, 4