Interest in vitamin D supplementation and testing has increased over the last few decades. Therefore, it’s only rational for concerns over toxicity and side effects to increase as well. A 16-year retrospective study evaluated the vitamin D status of patients at the University of Iowa Hospitals and Clinics (UIHC) to determine the risk of toxicity.
Researchers studied a total of 73,779 hospital patients and analyzed 127,932 serum blood samples to determine 25(OH)D status. For individuals with vitamin D levels above 120 ng/ml (300 nmol/l), or who displayed signs and symptoms of hypercalcemia, detailed medical reviews were conducted. Signs and symptoms of hypercalcemia were defined as excessive thirst, excessive urination, decreased appetite, vomiting, constipation, abdominal pain, renal failure, and/or failure to thrive.
This is what the researchers found:
- Only 1.05% of the participants had vitamin D levels above 80 ng/ml (200 nmol/l).
- Only 0.12% had levels that exceeded 120 ng/ml (300 nmol/l).
- Four patients showed symptoms of vitamin D toxicity, and three of these cases were caused by mistaken overdosing of liquid vitamin D supplements.
- The last case of toxicity was allegedly due to daily supplementation of 1,000 IU, but the researchers flagged this case for potentially inaccurate history.
The researchers concluded,
“Symptomatic vitamin D toxicity is uncommon, and elevated levels of 25(OH)D do not strongly correlate with clinical symptoms or total serum/plasma calcium levels. Our study highlights the potential risks of the liquid formulation of vitamin D.”