Vitamin D Toxicity: Symptoms and Risks
Yes, you can absolutely take too much vitamin D, which can lead to toxicity characterized by hypercalcemia, kidney damage, and various systemic symptoms. 1
Understanding Vitamin D Toxicity
Vitamin D toxicity typically occurs when serum 25(OH)D levels exceed 150 ng/mL (375 nmol/L), though levels above 100 ng/mL are concerning and warrant intervention 1. The upper limit of safety for vitamin D intake is generally considered to be 4,000 IU daily 1, though some guidelines suggest that risk of harm increases above 10,000 IU daily for prolonged periods 2, 1.
Risk Factors for Vitamin D Toxicity:
- Excessive supplementation (>10,000 IU daily for extended periods)
- Accidental overdose
- Manufacturing errors in supplements
- Genetic factors affecting vitamin D metabolism 1
Clinical Symptoms of Vitamin D Toxicity
Vitamin D toxicity can manifest with numerous symptoms affecting multiple body systems:
Common Symptoms:
- Hypercalcemia-related symptoms:
- Fatigue and weakness
- Confusion and altered mental status
- Nausea and vomiting
- Constipation
- Polyuria and polydipsia (increased urination and thirst)
- Kidney injury and kidney stones 1
Additional Manifestations:
- Bone abnormalities
- Dermatitis and skin disorders
- Alopecia (hair loss)
- Muscle pain
- Cheilitis (inflammation of the lips)
- Pseudotumor cerebri
- Hepatocellular necrosis
- Hyperlipidemia 1
Laboratory Findings
Key laboratory findings in vitamin D toxicity include:
- Elevated serum 25(OH)D levels (>150 ng/mL)
- Hypercalcemia
- Hyperphosphatemia
- Suppressed parathyroid hormone (PTH) levels
- Increased urinary calcium excretion
- Potentially elevated creatinine and BUN (indicating kidney dysfunction) 1
Case Example of Extreme Toxicity
A case report documented a 56-year-old woman who consumed an extremely high dose of cholecalciferol for 20 months (average 130,000 IU daily, cumulative 78,000 IU) following a non-conventional protocol for multiple sclerosis. She developed hypercalcemia (3.23 mmol/L), acute kidney injury, and had 25(OH)D levels of 920 nmol/L. After stopping supplementation, it took 6 months for her renal function and 18 months for vitamin D values to normalize 3.
Important Considerations
U-shaped Risk Curve
Research suggests a U-shaped relationship between vitamin D levels and cardiovascular risk, with increased risk at both low and high levels 2. This highlights the importance of maintaining optimal rather than maximum vitamin D levels.
Potential for Harm Without Classical Toxicity
Prolonged consumption of excessive vitamin D supplements may induce hypercalcemia, hypercalciuria, and hyperphosphatemia, which can lead to tissue and organ damage even without developing classical hypervitaminosis D 4.
Individual Variation
There exists significant inborn variation in people's ability to metabolize vitamin D, meaning some individuals may be injured by doses that are safe for others 2.
Management of Vitamin D Toxicity
If vitamin D toxicity is suspected:
- Immediately stop all vitamin D supplements
- Increase oral fluid intake to promote calcium excretion
- Consider IV hydration with normal saline for severe hypercalcemia
- Restrict dietary calcium intake temporarily
- Monitor serum calcium and vitamin D levels every 2-4 weeks initially
- In severe cases, consider loop diuretics (after adequate hydration) or bisphosphonates 1
Prevention
- Adhere to recommended supplementation guidelines (generally ≤4,000 IU daily)
- Consider monitoring serum calcium and phosphorus every 3 months during high-dose supplementation
- Educate patients about safe vitamin D supplementation
- Be aware that standard clinical doses rarely cause toxicity, but errors in dosing can occur 1, 3