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Monday 14th November, 2005
Calcium intake levels of more than 800 mg/day may be unnecessary
for maintaining calcium metabolism.
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
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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
"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."
Source: JAMA.2005; 294:2336-2341.
Editor's Note: This study was supported by a grant from the
Science Fund of St. Josephs Hospital, Landakoti, and the University
Hospital, Reykjavik, Iceland.