Published: Oct 30, 2013 | Updated: Oct 30, 2013
http://www.medpagetoday.com/Endocrinolo ... logy/42575
• Increasing vitamin D levels had no effect on calcium absorption in young women.
• Point out that the study suggests that there is no need to recommend vitamin D for increasing calcium absorption in normal people.
Increasing vitamin D levels had no effect on calcium absorption in young women, researchers reported.
In an ancillary result from a randomized clinical trial, women who started out with vitamin D insufficiency were brought up to normal levels through supplements over a 1-year period, according to Christopher Gallagher, MD, of Creighton University Medical Center in Omaha, and colleagues.
But the supplementation had no effect on calcium absorption at any dose, Gallagher and colleagues reported online in the Journal of Bone and Mineral Research.
The bottom line is that calcium absorption is very efficient, even at very low levels of vitamin D, the researchers argued.
"There is no need to recommend vitamin D for increasing calcium absorption in normal [people]," they concluded.
The study enrolled 198 Caucasian and African-American women, ages 25 to 45, with levels of serum 25-hydroxyvitamin D (25OHD) below 20 ng/ml.
They were randomly assigned in a double-blind fashion to placebo or one of four daily doses of cholecalciferol (vitamin D3) -- 400, 800, 1600, or 2,400 IU.
The participants were also given a daily calcium supplement to bring average calcium intake up from 706 mg/day at baseline to 1,031 mg/day during the 12-month study.
The primary endpoint of the study was to how much vitamin D3 was needed to increase serum 25OHD levels and normalize serum parathyroid hormone.
But a secondary outcome was to measure changes in calcium absorption because adequate calcium and phosphorous are required to avoid osteomalacia, the investigators noted.
The investigators measured calcium absorption at baseline and after 12 months using a single isotope method.
In a multivariate analysis, the researchers found that vitamin D dose did not predict the final 12-month calcium absorption.
Also, race was marginally predictive with African-American women tending to have lower absorption than Caucasians (P=0.053).
Total calcium intake (P<0.009), baseline weight (P=0.019), and baseline calcium absorption did predict absorption at 12 months (P=0.012).
But baseline serum levels of 25OHD and calcitriol (1,25(OH)2D) were not predictive.
Findings were similar for serum levels of 25OHD at 12 months, Gallagher and colleagues reported.
The study is the first randomized trial to look at the issue in younger women, the investigators concluded, and a study in older women, using similar doses, found much the same thing.
At higher vitamin D doses, however, there was a small increase in calcium absorption, they noted. Gallagher and colleagues also noted that analyses of adolescent girls and children have also found no increase in calcium absorption with higher levels of vitamin D.
They cautioned that the single isotope method of measuring calcium absorption is probably a less accurate technique than the double isotope approach, although results of the two types are highly correlated.
Vitamin D does not Increase Calcium Absorption in Young Women: A Randomized Clinical Trial
http://onlinelibrary.wiley.com/doi/10.1 ... 1/abstract
It is commonly said that vitamin D should be used to increase calcium absorption. We tested this statement in a dose response study of vitamin D on calcium absorption.
198 Caucasian and African American women, ages 25–45 years, with vitamin D insufficiency, serum 25OHD < 20ng/ml, were randomized in a double blind study to vitamin D3 400, 800, 1600, 2400 IU or placebo. A calcium supplement was given to increase mean calcium intake at baseline from 706 mg/day to 1031 mg/day. Calcium absorption was measured at baseline and after 12 months using a single isotope method with radiocalcium45 and 100 mg of calcium.
Mean baseline serum 25OHD was 13.4 ng/ml (33.5nmol/L) and increased to 40 ng/ml (100nmol/l) on the highest dose of 2400 IU. Using a multivariate regression analysis with significant predictors, baseline absorption, calcium intake and weight there was no increase in 12-month calcium absorption compared to baseline on any dose of vitamin D in either Caucasians or African Americans. There was no significant relationship between 12-month calcium absorption and final serum 25OHD. In an analysis of calcium absorption and serum 25OHD at baseline, serum 25OHD levels were divided into groups 0-5, > 6–10, > 11–15, > 16–20ng/ml. There was no evidence of a threshold decrease in calcium absorption nor serum 1,25(OH)2D amongst the lowest groups.
Vitamin D doses upto 2400 IU daily did not increase calcium absorption. No threshold level of serum 25OHD for calcium absorption was found at baseline or in the longitudinal study suggesting that active transport of calcium is saturated at very low serum 25OHD levels< 5ng/ml. There is no need to recommend vitamin D for increasing calcium absorption in normal subjects. Very efficient calcium absorption at very low levels of serum 25OHD explains why people do not develop osteomalacia provided that dietary intake of calcium and phosphorus is adequate. © 2013 American Society for Bone and Mineral Research
Oeps .. het heilige huisje: ’Vit.D suppletie is nodig voor calcium absorptie', wordt omver gekegeld.