Published: Feb 5, 2014
By Kristina Fiore, Staff Writer, MedPage Today
The body absorbs more calcium as vitamin D levels go up, and there’s no threshold to the effect – but the increases are small and current U.S. daily recommendations for vitamin D intake shouldn’t change, results of a randomized controlled trial suggest.
Some researchers have posited that there could be a level of vitamin D intake above which there’s no further influence on calcium absorption. If that were the case, doctors would have a cut-off to stop vitamin D supplementation since there’d be no additional benefits for skeletal health.
To determine whether that’s the case, John Aloia, MD, of Winthrop University Hospital in Mineola, N.Y., and colleagues gave various doses of vitamin D (or placebo) to 76 postmenopausal women – 800 IU, 2,000 IU, or 4,000 IU per day.
They found a linear increase in calcium absorption as the dose went up, at 3.9%, 5%, and 6.7%, respectively. (Calcium absorption fell by 2.6% for those who took placebo, showing the need for adequate vitamin D levels to maintain calcium absorption, the authors said.)
They said it’s likely that calcium absorption continues to rise at even higher doses of the vitamin, although these increases are minimal and current IOM recommendations for vitamin D intake of 600 to 800 IU per day shouldn’t change.
Given that the baseline serum vitamin D level was 63 nmol/L, the study didn’t look at low or deficiency levels, so the study won’t inform the possibility of a threshold effect for vitamin D in the deficiency range.
But Sue Shapses, PhD, of Rutgers University, who wrote an editorial on the study this month online in the American Journal of Clinical Nutrition (the original study was published in that journal in December), said the results clearly show that it’s “important to consume the recommended intakes of vitamin D and calcium to avoid low net calcium absorption and to maintain bone health.”
Shapses also praised the study for its use of the dual-isotope method to measure calcium absorption, which is “more precise” than other approaches.
It seems there’s at least one new study of the vitamin published every day, and in the Vitamin D Blog, MedPage Today will monitor that steady stream, offering our take on clinical implications — or limitations.
Have a tip on a vitamin D study? Email Kristina Fiore at k.fiore@medpagetoday.com. You can also catch our vitamin D feed on Twitter, @vitaminDblog.
Other coverage from the Vitamin D Blog:
Vitamin D Blog: VITAL Study Questions Answered
Vitamin D Blog: Need a Closer Look at D’s Role in COPD?
Vitamin D Blog: Does It Mark Pre-eclampsia Risk?