Side effects of high dose vitamin D supplementation
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High Dose Vitamin D Supplementation: Common Side Effects
Hypercalcemia and Hypercalciuria Risks
High dose vitamin D supplementation (typically 2800–10,000 IU/day) is associated with an increased risk of hypercalcemia (high blood calcium levels) and hypercalciuria (high urine calcium levels) compared to lower doses or placebo. The risk of hypercalcemia is about two times higher in those taking high doses, but the absolute number of cases remains low and most are mild and resolve on their own Zittermann2023Malihi2019Billington2019+1 MORE. Hypercalciuria is also more common with higher doses, especially at 10,000 IU/day, but does not always lead to kidney stones Billington2019Malihi2016.
Kidney Stones
Despite the increased risk of hypercalciuria, most studies do not show a significant increase in kidney stone formation with high dose vitamin D, whether given daily or as large monthly doses Malihi2019Malihi2016Malihi2019+1 MORE. In large trials, the rate of kidney stones was similar between those taking high dose vitamin D and those taking placebo .
Falls, Hospitalization, and Mortality
Some evidence suggests that high dose vitamin D (3200–4000 IU/day) may slightly increase the risk of falls and hospitalizations, but not overall mortality . The increase in falls and hospitalizations is small but statistically significant in some studies .
Bone Health and Density
High dose vitamin D supplementation (4000–10,000 IU/day) over several years may actually reduce bone density, especially in women. Studies show a dose-dependent loss of bone mineral density in females, raising concerns about the use of high dose vitamin D for bone health, particularly in postmenopausal women Burt2020Boucher2021. There is no evidence of benefit for bone health at these high doses, and possible harm in some groups .
Adverse Events in Special Populations
In renal transplant recipients, high dose vitamin D (100,000 IU every two weeks to monthly) did not increase the risk of adverse events compared to lower doses, suggesting it is generally safe in this population, though it did not reduce non-bone complications .
Autoimmune and Neurological Effects
In animal models, very high vitamin D levels can worsen autoimmune conditions like multiple sclerosis by increasing calcium levels and making immune cells more active and inflammatory. This suggests that extremely high doses may have unexpected negative effects on the immune system, at least in certain contexts .
General Tolerability
Most studies report that the overall rate of adverse events (any side effect) is similar between high dose vitamin D and placebo, with no significant increase in total adverse events, even with long-term use Malihi2019Malihi2019. Most side effects are mild and transient.
Conclusion
High dose vitamin D supplementation increases the risk of hypercalcemia and hypercalciuria, but these events are usually mild and do not often lead to kidney stones. There may be a small increase in falls and hospitalizations, and high doses can reduce bone density in women. For most people, high dose vitamin D is generally well tolerated, but caution is advised, especially for long-term use and in populations at risk for bone loss or autoimmune disease. Regular monitoring of calcium levels is recommended when using high dose vitamin D.
Sources and full results
Most relevant research papers on this topic
Adverse events from large dose vitamin D supplementation taken for one year or longer.
Long-term high-dose vitamin D supplementation (≥2800 IU/d) did not significantly increase the risk of total adverse events or kidney stones, but showed a trend towards increased hypercalcemia.
Safety of High-Dose Vitamin D Supplementation: Secondary Analysis of a Randomized Controlled Trial.
High-dose vitamin D supplementation (up to 10,000 IU/day) is generally safe, with mild and transient hypercalcemia occurring more frequently at higher doses.
Hypercalcemia, hypercalciuria, and kidney stones in long-term studies of vitamin D supplementation: a systematic review and meta-analysis.
Long-term vitamin D supplementation increases the risks of hypercalcemia and hypercalciuria, but does not increase the risk of kidney stones.
Monthly high-dose vitamin D3 supplementation and self-reported adverse events in a 4-year randomized controlled trial.
Monthly high-dose vitamin D3 supplementation for up to 4 years did not significantly affect participant-reported adverse events.
Nonskeletal and skeletal effects of high doses versus low doses of vitamin D3 in renal transplant recipients: Results of the VITALE (VITamin D supplementation in renAL transplant recipients) study, a randomized clinical trial.
High doses of cholecalciferol are safe after renal transplantation but do not reduce extraskeletal complications.
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