Can I have too much Vitamin D?

Vitamin D has a wide margin of safety, and that means that the toxic dose of Vitamin D is many, many times higher than the dose needed for health benefits. As such, Vitamin D overdose and toxicity are extremely rare when taken according to the recommended or prescribed doses.^1-3

Prolonged exposure to sunlight cannot cause Vitamin D overdose as our skin automatically limits its production of Vitamin D.⁴ That said, we know to avoid overexposure to harmful UV rays without adequate protection as it can increase the risk for skin cancer. You are also highly unlikely to overdose on Vitamin D through your diet as most foods do not contain high enough amounts of Vitamin D. Even eating large portions of Vitamin D-rich food like fatty fish would not exceed the maximum daily intake limit.⁵

Taking an oral Vitamin D supplement according to the product label or as a medication at the dose prescribed by a doctor is generally well tolerated and safe, and rarely causes side effects or toxicity.^1,2 However, accidentally or intentionally taking doses of Vitamin D supplements or medications above the recommended upper limits can be dangerous.²

Although symptoms of Vitamin D toxicity are still rare at doses below 10,000 IU a day (equivalent to 300,000 IU/month), the recommended daily upper limit is 4,000 IU (equivalent to 120,000 IU/month) for healthy individuals aged 9 years and older.⁵ This is owing to adverse effects being observed with long-term consumption of Vitamin D at ranges above or near the upper limit.⁵ Doses higher than 10,000 IU per day should never be taken without medical supervision.

At blood levels above 60 ng/mL (150 nmol/L), Vitamin D can cause health problems.⁵ Toxic Vitamin D levels lead to excessive calcium levels in the blood (hypercalcaemia), and often high phosphate and calcium in urine. The adverse health effects of Vitamin D toxicity are caused by these abnormally high calcium levels rather than the Vitamin D itself.²

Common symptoms of acute (sudden, short-term) Vitamin D toxicity can include nausea, dehydration, increased urination, and constipation.^2,3 Adverse effects associated with chronic (slow onset, long-term) Vitamin D toxicity include calcium deposits in the kidneys, heart problems, loss of calcium from bones, and sometimes bone and muscle pain.^1-3

Once again, Vitamin D toxicity is rare and usually only occurs if Vitamin D supplementation is not properly monitored. Patients with Vitamin D deficiency may receive high doses to restore their levels to normal, but always under a doctor’s supervision and for only a limited period.^2,3 When in doubt, consult your healthcare provider for more information on Vitamin D supplementation and what works best for you based on your risk profile, lifestyle and medical history.

References
1) Chang SW, Lee HC. Pediatr Neonatol 2019;60:237-244.
2) Kennel KA, et al. Mayo Clin Proc 2010;85:752-757.
3) MIMS Singapore. D-Cure^® (vitamin D) [prescribing information]. Available at:
https://www.mims.com/singapore/drug/info/d-cure?type=full. Accessed 1 July 2021.
4) National Institutes of Health. Vitamin D Fact Sheet for Consumers. Available at:
https://ods.od.nih.gov/factsheets/VitaminD-Consumer/. Accessed 30 June 2021
5) National Institutes of Health. Vitamin D Fact Sheet for Health Professionals. Available at: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/. Accessed 30 June 2021.