NEW DIETARY RECOMMENDATIONS FOR MAGNESIUM, CALCIUM,
PHOSPHORUS, AND VITAMIN D: SOME CONCERNS
FRANZ KBa, SEELIG MSb aBrigham Young
University, Provo, UT, USA; bUniversity of North
Carolina, School of Medicine, Chapel Hill, NC, USA
Key Words: magnesium, calcium, phosphorus,
vitamin D, DRI, RDA, AI, UL, eclampsia, syndrome X, hypertension,
cardiovascular disease, diabetes mellitus
New dietary standards are being developed in the United
States, and Canada to replace the Recommended Dietary Allowances
(RDAs) of 19801, that were revised in
19892, and the 1990 recommendations from Health
Canada. The RDAs were established to prevent deficiency diseases;
the new standards, termed Dietary Reference intakes (DRIs), are
intended to provide amounts of nutrients that will help in
achieving and maintaining optimum health and limit chronic
disease. The Food and Nutrition Board (of the Institute of
Medicine, National Academy of Sciences, the United States)
presented DRIs for magnesium (Mg), calcium (Ca), phosphorus (P),
and vitamin D in August 1997.3
The New Dietary Standards (Table 1): As part
of the new DRIs, additional terms are introduced. Adequate Intake
(AI) is a new term that is similar to the RDA, but that is based
on less extensive evidence. The new term, the Estimated Average
Requirement (EAR) is a median requirement to meet the needs of
50% of an age and gender group. RDAs were set for Mg and P based
on their EARs. Since there were too few data to set EARs for Ca
and vitamin D, only AIs were designated. A third new term is the
Tolerable Upper Intake Levels (UL), from both food and
supplements, that applies to Ca, P, and vitamin D. The UL for Mg
is the intake only from supplements. The UL designates the
maximum amount that is unlikely to pose risks of adverse health
effects. It is not the recommended level of intake.
Table I. The 1997 DRIs for magnesium, calcium,
phosphorus, and vitamin D.
|
Age
|
Mg-RDA(mg)
|
Ca-AI(mg)
|
P-RDA(mg)
|
Vitamin D-AI(ug)
|
|
Years
|
M
|
F
|
M&F
|
M&F
|
M&F
|
|
14-18
|
410*
|
360*
|
1300*
|
1250*
|
5**
|
|
19-30
|
400*
|
310*
|
1000**
|
700**
|
5**
|
|
31-50
|
420*
|
320*
|
1000*
|
700**
|
5**
|
|
51-70
|
420*
|
320*
|
1200*
|
700**
|
10*
|
|
>70
|
420*
|
320*
|
1200*
|
700**
|
15*
|
|
Pregnant
|
|
|
|
|
|
|
<19
|
|
400***
|
1300*
|
1250*
|
5**
|
|
19-30
|
|
350***
|
1000**
|
700**
|
5**
|
|
31-50
|
|
360***
|
1000**
|
700**
|
5**
|
-------------------------------------------------------------------------------------------------
*Above 1989 RDA; **Below 1989 RDA; ***Above 1989 but below 1980
RDA
DRIs are higher for Mg, than they were in the 1989 RDAs, but
lower than in the 1980 RDAs for pregnant women. For Ca and P, the
DRIs are lower than the RDAs for some but higher for others.
Adult Ca intake is increased from 800 mg to 1000 mg for adults up
to the age of 50 years, and further increased to 1200 mg for
those older than 50. Adult DRIs for vitamin D are similar to the
previous RDAs for young adults, but are higher for those older
than 50. Ca and vitamin D recommendations for older adults were
increased largely to prevent osteoporosis. ULs (Table II) were
developed to provide guidelines for supplements and for
nutritional fortification of foods.
Table II. The tolerable upper limits (UL) for
magnesium, calcium, phosphorus, and vitamin D.
|
Age
|
Mg*(mg)
|
Ca**(mg)
|
P**(mg)
|
Vitamin D*
|
|
Years
|
M&F
|
M&F
|
M&F
|
M&F
|
|
All ages
|
350
|
2500
|
3500
|
50
|
-------------------------------------------------------------------------------------------------
For Mg, UL is intake only from supplements; does not include Mg
in food and water.
For Ca, P, and vitamin D, includes the total intake from food,
water, and supplements.
Some Concerns: The UL of Mg was estimated as
the amount that will cause the least diarrhea, even in the
minority with intestinal sensitivity to Mg
supplementation.3 This low UL for Mg may induce some
in the medical community to restrict Mg supplementation to the UL
for all individuals, even though higher amounts are needed by
some, certainly during pregnancy, by those with familial
predisposition to cardiovascular diseases in which low
intracellular (i.c.) Mg has been identified, and by normal
persons undergoing stress.4-6 This has recently been
illustrated by the beneficial effect of 411-548 mg Mg/day on
blood pressure and HDL-cholesterol, in apparently healthy
individuals.7
In contrast to the low UL for Mg supplements (350mg), the UL
for Ca is high (2500 mg). Allowing for addition of the
supplemental Mg to the customary Mg intake of about 300, the
intake of some could reach ratios exceeding 5:1 by those
ingesting the UL for Ca. Might the ULs of Ca and vitamin D be
interpreted by some in the medical community as more desired
intakes than the AIs for these nutrients, even though this was
not the intent of these recommendations? More information is
needed about the impact of UL levels of intake of Ca and vitamin
D upon intestinal Mg absorption, distribution in the body, and
renal excretion, particularly by those with low Mg intake.
Although the RDA for P was decreased for adults, dietary
intakes of P are usually much higher. P can come in several
different forms in the diet; some are better absorbed by the
intestines than others. About 65% of food P is absorbed, but
phytic acid8 or polyphosphate additives to
food,9 are poorly absorbed. The unabsorbed P binds to
Ca and Mg ions and decreases their absorption.8 If
3500 mg of P were consumed in the diet and 65% was absorbed, this
would result in 1225 mg of fecal P. If dietary Mg were low, its
decreased absorption through binding to P, could result in
increased risk of Mg deficiency, as a result of fecal excretion
of more Mg than was ingested. With poorly absorbed P compounds,
critical levels of stool P that adversely affect intestinal Mg
absorption could be achieved with P intakes lower than the
UL.
The negative impact of high dietary Ca: Mg ratios on Mg in the
body, which has been implicated in the high cardiovascular
disease morbidity and mortality in Finland,10 might be
contributed to by the P that often accompanies high Ca intake,
with subsequent impact on intestinal Mg absorption.8 A
liter of skim milk contains about 1270 mg Ca, 135 mg Mg, and 1035
mg P. The dietary P:Mg ratio may be as important as, or in those
with high milk diets or with intake of other high P foods or
drinks, be even more significant than the dietary Ca-Mg ratio
because of the greater impact of P on Mg intestinal
absorption.
On the other hand, increasing use of high dose Ca supplements
(e.g. to prevent or limit progression of
osteoporosis11,12), or as reflected by a recent large
study of administration of 2 grams of supplemental Ca to see if
it would prevent eclampsia,13 puts the emphasis on
potential risks of high Ca:Mg intakes. Ca supplementation did not
prevent eclampsia among the 2295 women given the Ca, as compared
with 2294 given placebo. Data were provided in tables that
indicate somewhat worse outcomes in Ca supplemented than in
control mothers. Occurring more often in the Ca-group than in the
controls were: 1.) HELLP, an uncommon severe toxemic -syndrome
comprising hemolysis, elevated hepatic enzymes, and low platelet
count (7 versus 2); 2.) small for gestational age infants (124
versus 105); 3.) preterm births (344 versus 314); 4.) infants
requiring intensive care (343 versus 315); and 5.) neonatal
deaths (12 versus 6). No data were given as to Mg intakes or
status. Low dietary Mg intakes are common in the U.S.A. both in
low and average income pregnant women.14 In Hungary,
there is high prevalence of spontaneous abortions and preterm
births in low Mg areas;15, 16 and early Mg
supplementation during pregnancy has been
beneficial,15 a finding also in a double-blind study
in Germany.17
Insight into why Mg supplementation during pregnancy protects
both mother and fetus, while high Ca intake does not, is provided
by elucidation of pathogenic mechanisms of eclampsia, which
involve placental pathology - caused by platelet aggregation and
adhesion and enhancement of the coagulation cascade, which
enhance likelihood of thrombosis, and by endothelial damage with
release of vasoconstricting thromboxane.18,19 These
reactions are inhibited by Mg,20-22 while Ca has
reciprocal effects.21 It has been hypothesized that
low Mg is the unifying factor in pregnancy pathologies, and that
early Mg supplementation might prevent much pregnancy-induced
disease.24
An ionic hypothesis attributes to low i.c. free Mg and excess
cytosolic free Ca, such clinically disparate disorders as
Syndrome X, which includes obesity, insulin-resistance,
hyperinsulinemia, non-insulin-dependent diabetes mellitus and
left ventricular hypertrophy, as well as hypertension and
atherosclerosis.25 Higher ionized Ca:Mg ratio in
cells, in comparison with that in normal individuals, has been
reported in atherosclerosis and essential
hypertension,26,27 hypertension associated with
preeclampsia28,29 and during labor,30 and
diabetes mellitus whether or not associated with
pregnancy.25, 28, 31 Usually, ionized Ca is increased
or normal as ionized Mg is decreased. Is this cellular imbalance
due to chronic Mg deficiency in the body or factors that directly
increase Ca uptake - be they dietary, from use of supplements,
hormonal, or other? If cellular ionized Ca is increased or normal
and ionized Mg is decreased, increasing dietary Ca, or providing
large Ca supplements without a concomitant increase in Mg intake
seems imprudent.
References
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