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Taking 4,000 IU of vitamin D daily seems safe

This randomized controlled trial followed 2,423 adults with overweight and prediabetes for a median of three years. It found that a daily dose of 4,000 IU of vitamin D3 (the official tolerable upper intake level in the U.S. and the E.U.) did not increase the risk of adverse events.


The tolerable upper intake level (UL) (i.e., the highest level of nutrient intake that is likely to pose no risk of adverse health effects for almost all individuals in the population) for vitamin D is 4,000 IU/day, which was set on the basis of preventing the primary indicator of vitamin D toxicity — hypercalcemia (i.e., high blood calcium levels). However, there is a scarcity of direct evidence demonstrating the safety and tolerability of high-dose daily vitamin D supplementation in the long term.

The study

In this randomized controlled trial, 2,423 participants (average age of 60; average 25-hydroxyvitamin D level of 28 ng/mL) with overweight or obesity and prediabetes were assigned to ingest either 4,000 IU of vitamin D3 or a placebo daily over a median follow-up period of 3 years.

In-person follow-up visits occurred at months 3 and 6 and then twice per year, with phone or email contact between visits to monitor adverse events. An adverse event was defined as any unfavorable and unintended medical occurrence (whether or not it was considered related to the study), and serious adverse events were any adverse event that resulted in death, a life-threatening event, or hospitalization. Key adverse events of interest were hypercalcemia, hypercalciuria (i.e., excess calcium in the urine), low estimated glomerular filtration rate (an indicator of impaired kidney function), and kidney stones.

The results

A total of 8,304 adverse events occurred during follow-up. The incidence rate of total adverse events was lower in the vitamin D3 group than in the placebo group. There was no difference between groups for the incidence of serious adverse events, nor was there a difference between groups for the incidence of hypercalcemia, hypercalciuria, low estimated glomerular filtration rate, or kidney stones.


These results suggest that the UL for vitamin D may be higher than the current level of 4,000 IU/day for adults with overweight or obesity and prediabetes.

There are 8 more summaries in the Vitamins & Minerals category for April 2022 including ...

  • Magnesium levels and Alzheimer’s disease
  • The effect of a single high dose of vitamin D on COVID-19
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