Are Some People Overdosing on Vitamin D?

Who has not had their serum vitamin D levels tested at some time in the last 10 years?

Some say vitamin D is the new vitamin C, at least for those of us in the rheumatology community: deficiency in vitamin D has been implicated in poor joint health, muscle weakness, and chronic pain. Vitamin supplements aplenty are available, and poised to cure so many of the ailments that make life a little more miserable than it really should be.

The vast majority of us who have been tested display normal or deficient levels of vitamin D. But should we worry about toxicity?

An analysis, the results of which were published earlier this year in the journal, “Laboratory Medicine,” set out to examine whether symptomatic vitamin D toxicity is a common phenomenon.

Vitamin D toxicity has been reported in a variety of age groups and from multiple causes, including errors in manufacturing, errors in milk fortification, incorrect dosing from liquid preparations, and intentional (although with no intent to harm) ingestion of megadoses of vitamin D supplements (apparently a result of thinking that something so good can never be too much). Among these causes, the most harmful appears to be sustained ingestion of megadoses (for example, 50,000 IU) and incorrect dosing of supplements in children. The researchers performed a review of the medical records of patients with elevated vitamin D levels during a 16-year period at an academic medical center, in an effort to describe the causes of hypervitaminosis D and the extent to which vitamin D levels correlate with serum calcium levels and clinical symptoms.

Symptoms of vitamin D toxicity include the following (in the absence of any other diagnosable cause): polydipsia (excessive drinking of water), polyuria (excessive urination), decreased appetite, vomiting, constipation, abdominal pain, renal failure, kidney stones, and/or failure to thrive.

Based on the reported history, 0.1% of patients reviewed had extremely high vitamin D levels: 17 patients were taking 50,000-IU tablets, four were taking 20,000-IU tablets, six were taking 10,000-IU tablets, 11 were taking 5000-IU tablets, and six were taking 1000-IU tablets. Also, seven were taking liquid formulations with varying concentrations. The remaining patients were reportedly taking a combination of multivitamin and "other" supplements. Eighteen patients had no vitamin D supplementation recorded in their medical record.

Nonetheless, symptomatic vitamin D toxicity was rare.

So, does this mean that we can feel free to take large amounts of vitamin D? No. There remain concerns about the long-term exposure to high vitamin D serum levels; as always, moderation in all things. You will feel better, and your doctor won’t be calling you night and day to come in for repeat tests of vitamin D levels.