Calcium intake of over 800 milligrams per day has been recommended for men and women, but obtaining this level from one's diet can be challenging. However, a report published in the November 9 2005 issue of the Journal of the American Medical Association revealed that taking over 800 milligrams calcium per day may not be necessary if one consumes enough vitamin D.
Laufey Steingrimsdottir, PhD, at Landspitali-University Hospital in Reykjavik, Iceland, and colleagues studied 944 adults who were divided according to calcium intake and serum vitamin D levels. Food frequency questionnaires provided data on calcium and vitamin D intake and blood serum samples were analyzed for hydroxyvitamin D and parathyroid hormone (PTH) levels. Parathyroid hormone helps maintain normal concentrations of calcium and is regulated via levels of calcium and calcitriol, the biologically active form of vitamin D.
Calcium and vitamin D insufficiency is associated with an increase in parathyroid hormone.
While participants in the high vitamin D group, whose vitamin D levels were over 18 nanograms per milliliter, had the lowest parathyroid levels, parathyroid levels were highest among those whose vitamin D levels were in the low group. Among those in the low vitamin D group, subjects whose calcium intake was also low at less than 800 milligrams per day had the highest parathyroid levels. Having a low calcium intake did not impact parathyroid levels in the group with high vitamin D, and having a high calcium intake but low vitamin D did not lower parathyroid levels below those measured in the high vitamin D group.
The authors concluded, "Our study suggests that vitamin D sufficiency may be more important than high calcium intake in maintaining desired values of serum PTH. Vitamin D may have a calcium sparing effect and as long as vitamin D status is ensured, calcium intake levels of more than 800 mg/d may be unnecessary for maintaining calcium metabolism. Vitamin D supplements are necessary to ensure adequate vitamin D status for most of the year in northern climates."
Laufey Steingrimsdottir; Orvar Gunnarsson; Olafur S. Indridason; Leifur Franzson; Gunnar Sigurdsson. Relationship Between Serum Parathyroid Hormone Levels, Vitamin D Sufficiency, and Calcium Intake. JAMA. 2005;294:2336-2341.