Study compares winter dosages of vitamin D3 in young healthy adults
“The aim of our study was to determine whether doses of 1000 IU or 2000 IU of vitamin D3 are sufficient for achieving and maintaining the reference values 75–200 nmol/L of [25(OH)D] in a sample of healthy young people during the winter months in the Czech Republic, a time when there is no natural synthesis of vitamin D,” the researchers wrote.
The study, published in the journal Life, noted the scarcity of research into the effect of 1000 IU and 2000 IU vitamin D3 supplementation in healthy populations during the winter at similar latitudes.
A total of 72 healthy volunteers (50 female and 22 male medical students) between the ages of 20 and 27 consumed two or four drops of a vitamin D3 solution (500 IU of vitamin D3 per drop) a day for 60 days with a 30-day break after each 60-day period. The researchers acknowledged the lack of a crossover or placebo control as limitation but noted “that studies with a more complicated design are not common in vitamin D research.”
“Our results show that a daily dose of either 1000 IU or 2000 IU of vitamin D3 is an adequate choice for maintaining sufficient vitamin D levels during the winter months,” the researchers wrote. “A daily dose of 2000 IU was, however, observed to maintain the desired levels of serum vitamin D concentration for a longer period than a daily dose of 1000 IU and can thus be recommended for supplementing young healthy individuals during the winter months.”
Results confirmed both doses as safe for substitution therapy, with circulating levels remaining below an established upper limit of 200 nmol/L. Calcium and phosphate concentrations remained stable throughout the study, and there were no statistically significant differences between the sexes, although circulating levels were higher in female participants using hormonal contraceptives as shown in other studies.
No need for testing at these levels
Commenting independently on the study results, Dr. Michael Holick, professor of medicine at the Boston University Chobanian & Avedisian School of Medicine and a leading authority on Vitamin D, noted that the study nicely demonstrates that either 1000 IUs or 2000 IUs is perfectly safe in healthy adults even if they are vitamin D sufficient.
“There has always been concern that before taking vitamin D supplementation that a blood level should be checked for 25-hydroxvitamin D,” he said. “This test is expensive and not always available. This study demonstrates that there is no need to be tested, that an adult can take 1000 or 2000 IU daily and not be concerned about toxicity.”
He noted that information about vitamin D supplementation and sun exposure leading up to the study would have been helpful since the median blood level of the study participants at baseline was 75 nmol/l, within the range of vitamin D sufficiency.
Source: Life 2023, 13(3), 808
“Vitamin D3 Supplementation: Comparison of 1000 IU and 2000 IU Dose in Healthy Individuals”
Authors: Eva Dědečková et al.