Adequate Vitamin D Status Appears More Important Than High Calcium
Intake for Maintaining Calcium Metabolism

CHICAGO - Calcium intake levels of more than 800 mg/day may be
unnecessary for maintaining calcium metabolism if vitamin D status is
adequate, according to a study in the November 9 issue of JAMA.

The importance of adequate vitamin D status for optimum bone health has
received increased recognition in recent years, with higher recommended
intake levels being proposed by some investigators, according to
background information in the article. The ideal intake is not known,
and different criteria have been proposed for estimating population
requirements. Serum 25-hydroxyvitamin D  has been the generally
accepted indicator of vitamin D status, but no universal consensus has
been reached regarding which serum values constitute sufficiency. An
inverse relationship between serum 25-hydroxyvitamin D and serum
parathyroid hormone (PTH) is well established. Parathyroid hormone is a
major hormone maintaining normal serum concentrations of calcium and
phosphate and is itself regulated through levels of calcitriol and
serum calcium. An insufficiency of vitamin D or calcium is generally
associated with an increase in PTH.

Laufey Steingrimsdottir, Ph.D., of Landspitali-University Hospital,
Reykjavik, Iceland, and colleagues conducted a study to determine the
importance of high calcium intake and serum 25-hydroxyvitamin D for
calcium homeostasis (metabolic equilibrium) in healthy adults, as
determined by serum intact PTH. The study included 2,310 healthy
Icelandic adults who were divided equally into 3 age groups (30-45
years, 50-65 years, or 70-85 years) and recruited from February 2001 to
January 2003. They were administered a semi-quantitative food frequency
questionnaire, which assessed vitamin D and calcium intake.
Participants were further divided into groups according to calcium
intake (less than 800 mg/d, 800-1200 mg/d, and greater than1200 mg/d)
and serum 25-hydroxyvitamin D level (less than 10 ng/mL, 10-18 ng/mL,
and greater than 18 ng/mL).  A total of 944 participants completed the
dietary questionnaire.

The researchers found that after adjusting for relevant factors, serum
intact PTH was lowest in the group with a serum 25-hydroxyvitamin D
level of more than 18 ng/mL but highest in the group with a serum
25-hydroxyvitamin D level of less than 10 ng/mL. At the low serum
25-hydroxyvitamin D level (less than 10 ng/mL), calcium intake of less
than 800 mg/d vs. more than 1200 mg/d was significantly associated with
higher serum PTH; and at a calcium intake of more than 1200 mg/d, there
was a significant difference between the lowest and highest vitamin D
groups.

"The significance of our study was demonstrated by the strong
negative association between sufficient serum levels of
25-hydroxyvitamin D and PTH, with calcium intake varying from less than
800 mg/d to more than 1200 mg/d. Our results suggest that vitamin D
sufficiency can ensure ideal serum PTH values even when the calcium
intake level is less than 800 mg/d, while high calcium intake (greater
than 1200 mg/d) is not sufficient to maintain ideal serum PTH, as long
as vitamin D status is insufficient," the authors write.

"Although a cross-sectional study such as our study is not sufficient
to demonstrate causality, the association between vitamin D status,
calcium intake, and the interaction between these 2 with serum PTH
levels is a strong indication of the relative importance of these
nutrients," the researchers write. "Although ideal intakes of these
2 nutrients need to be further defined in more elaborate studies, there
is already sufficient evidence from numerous studies for physicians and
general practitioners to emphasize to a much greater extent the
importance of vitamin D status and recommend vitamin D supplements for
the general public, when sun exposure and dietary sources are
insufficient."

"In conclusion, 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."

JAMA.2005; 294:2336-2341.

Editor's Note: This study was supported by a grant from the Science
Fund of St. Josephs Hospital, Landakot, and the University Hospital,
Reykjavik, Iceland.