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Calcium absorption varies within the reference range for serum 25-hydroxyvitamin D.
Robert P Heaney1, M Susan Dowell, Cecilia A Hale
1Creighton University, 601 N. 30th Street, Suite 4841, Omaha, NE 68131, USA. rheaney@creighton.edu
Journal of the American College of Nutrition
|April 4, 2003
Summary
Higher vitamin D levels significantly improve calcium absorption in humans. Even vitamin D levels within the current reference range may be too low for optimal calcium absorption.
Area of Science:
- Human physiology
- Nutritional science
- Endocrinology
Background:
- Calcium absorption is known to be reduced in vitamin D deficiency.
- Optimal vitamin D levels for normalizing calcium absorption in humans remain unclear.
Purpose of the Study:
- To quantify calcium absorption at two distinct vitamin D repletion levels.
- Utilize pharmacokinetic methods and standard calcium supplements to assess absorption.
Main Methods:
- Two experiments were conducted with participants receiving oral calcium loads.
- Serum 25-hydroxyvitamin D (25OHD) concentrations were maintained at approximately 86.5 nmol/L (pretreated) and 50.2 nmol/L (unpretreated).
- Calcium absorption was estimated by measuring the area under the curve (AUC) of serum total calcium increments.
Main Results:
- Calcium absorption was 65% higher in participants with a mean serum 25OHD of 86.5 nmol/L compared to those with 50.2 nmol/L.
- Both tested 25OHD levels were within the nominal reference range.
- A statistically significant difference (P < 0.001) in absorption was observed between the two groups.
Conclusions:
- Calcium absorption is significantly reduced at serum 25OHD levels of 50 nmol/L compared to 86 nmol/L.
- Current reference ranges for serum 25OHD may be set too low, potentially impacting calcium absorption.
- Individuals with 25OHD levels at the lower end of current ranges may not fully benefit from calcium intake.