NEW YORK (Reuters Health) – A single 45,000-IU dose of vitamin D3 given every 4 weeks is as safe as smaller daily or weekly doses and is as effective in achieving protective levels of serum 25-hydroxyvitamin D, according to a study conducted in Israel.

“A recent consensus concluded that to prevent fractures in older patients, the serum 25(OH)D concentrations should be higher than 30 ng/mL,” Dr. Sophia Ish-Shalom and colleagues explain in the Journal of Clinical Endocrinology and Metabolism for September. While monthly dosing could improve adherence, they were concerned that the large dose could cause transient hypercalcemia.

The team conducted a randomized trial among 48 women, mean age 81 years, who had undergone surgery to repair hip fracture, to compare three dosing regimens of vitamin D3 supplementation: 1,500 IU once daily, 10,500 IU once weekly, or 45,000 IU every 28 days. The vitamin was dissolved in ethanol and added to a drink.

After 2 months, serum levels of 25-hydroxyvitamin D were similar at 33.2, 29.2, and 37.1 ng/mL, respectively.

The monthly dose produced an initial transient increase in serum 1,25-dihydroxyvitamin D after the first, but not the second dose.

A single case of hypercalcemia occurred, in a patient assigned to the daily supplement.

Dr. Ish-Shalom, at Rambam Medical Center in Haifa, Israel, and associates conclude: “The choice of dose frequency can be based on whichever approach will optimize an individual’s adherence with long-term vitamin D supplementation.”

“Furthermore,” they add, “if a daily or weekly dose is missed and later remembered, then it can be taken as soon as it is remembered, or it can be added to the next dose.”

J Clin Endocrinol Metab 2008;93:3430-3435.