Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride (1997) / Chapter Skim
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6 Magnesium
6 Magnesium
Pages 190-249
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From page 190... ...
Extracellular magnesium accounts for about 1 percent of total body magnesium. The normal serum magnesium concentration is 0.75 to 0.95 mmol/ liter (1.8 to 2.3 mg/~1~.
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From page 191... ...
Magnesium transport in mammalian cells may be influenced by hormonal and pharmacological factors including ,3-agonists, growth factors, and insulin (Gunther, 1993; Hwang et al., 1993; Romani et al., 1993~. It has been suggested that a hormonally regulated magnesium uptake system controls intracellular magnesium concentration in cellular compartments.
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From page 192... ...
Both an unsaturable passive and saturable active transport system for magnesium absorption may account for the higher fractional absorption at low clietary magnesium intakes (Fine et al., 1991 a)
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From page 193... ...
Despite the close regulation of magnesium by the kidney, no one has clescribeci a hormone or factor that is responsible for renal magnesium homeostasis. Because patients with either primary hyper- or hypoparathyroiclism usually have normal serum magnesium concentrations and a normal tubular maximum for magnesium, it is probable that parathyroici hormone (PTH)
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From page 194... ...
Increased calcium intake clici not affect magnesium balance when as much as 2,000 mg (50 mmol) /ciay of calcium was given to adult men (Spencer et al., 1978b, 1994)
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From page 195... ...
Plasma/serum magnesium concentrations have been reported to fall with chronic endurance exercise activity, while red blood cell values appear to rise (Deuster and Singh, 1993~. Although the decrease in plasma magnesium has been suggested to reflect magnesium depletion in athletes (Clarkson and Haymes, 1995)
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From page 196... ...
Total magnesium intake is usually dependent on caloric intake, which explains the higher intake levels seen in the young and in adult males and the lower levels seen in women and in the elderly. Water is a variable source of intake; typically, water with increased "hardness" has a higher concentration of magnesium salts.
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From page 197... ...
In considering ciata from such studies, it is important to separate the identification of associations between the effect of the disease on magnesium status from the effect of inadequate intake on magnesium status and subsequent risk of disease. The specific disease states in which magnesium status is implicated are cliscusseci in the following sections.
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From page 198... ...
Magnesium depletion in patients with cardiac diseases may be due to concomitant medications, such as diuretics, as well as to dietary magnesium depletion. Although cardiac arrhythmia may be associated with the primary cardiac disorders, magnesium depletion may further predispose to cardiac arrhythmias by decreasing intracellular potassium.
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From page 199... ...
/day to 423 mg (17.6 mmol) /day, significantly lowered blood pressure in adults who were not classifieci as hypertensive (systolic blood pressure < 140 mm Hg; diastolic blood pressure < 95 mm Hg ~ (Appel et al., 1997~.
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From page 200... ...
In patients with essential hypertension, free magnesium levels in erythrocytes were inversely related to both the systolic and diastolic blood pressure (Resnick et al., 1984~. It is unclear whether the decrease in serum magnesium concentration was due to magnesium depletion or to pathophysiological events that lead to hypertension.
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From page 201... ...
Magnesium clepletion in clinical observational studies has been clefineci by low serum magnesium concentrations as well as a reduction of total anci/or ionized magnesium in reci blood cells, platelets, lymphocytes, and skeletal muscle (Naciler et al., 1992) , in spite of subjects consuming a level of magnesium similar to that in population studies (Schmidt et al., 1994~.
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From page 202... ...
is thought to indicate magnesium clepletion (Elin, 1987~. Experimentally induced dietary magnesium depletion consistently leacis to clecreaseci serum magnesium values in otherwise healthy humans.
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From page 203... ...
There are also reports that elderly subjects may have a decrease in magnesium status as cletermineci by magnesium tolerance testing (see below) despite normal serum magnesium concentrations.
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From page 204... ...
Lymphocyte magnesium clods not correlate well with serum or reci blood cell magnesium levels (Elin and Hosseini, 1985; Ryzen et al., 1986) and serum magnesium concentration clods not accurately reflect muscle magnesium content (Alfrey et al., 1974; Wester and Dyckner, 1980~.
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From page 205... ...
Some provicleci for a period of adaptation but clici not include magnesium intakes, which would have allowed average requirements to be estimateci. Balance studies performed prior to 1960 utilized less accurate means to measure magnesium as compared with atomic absorption spectrophotometry.
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From page 206... ...
While the magnesium tolerance test has been shown in this and other studies (Cohen and Laor, 1990; Costello et al., 1997; Gullestaci et al., 1992) to detect magnesium clepletion in both hypomagnesemic and normomagnesemic subjects at risk of magnesium depletion, the test was not sensitive to detect treatment effects of magnesium supplementation in otherwise healthy subjects (Costel
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From page 207... ...
who were stated to have "lower than recommencleci clietary magnesium intakes." Subjects with serum magnesium less than 0.59 + 0.07 mmol/liter (1.4 + 0.2 mg/cil) retained a higher percentage of the magnesium loaci (61 + 12 percent)
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From page 208... ...
The limited ciata on magnesium balance in infants were consiclereci supportive evidence for the cleriveci AI. Many of the magnesium balance studies involving human milk-feci infants have been performed on premature infants or infants in the first weeks of life.
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From page 209... ...
Thus, magnesium intake from human milk with an average magnesium concentration of 34 mg ~ 1.4 mmol) /liter would be about 20 mg (0.8 mmol)
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From page 210... ...
Direct assessment of an AI for magnesium for formula-feci infants is not possible clue to the lack of ciata comparing magnesium absorption from human milk and from infant formulas. Baseci on the current U.S.
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From page 211... ...
were not consiclereci because information regarding absorption over a range of intakes was not provicleci and results reported may not be reliable using the analytical methodology available at that time. Given the information provicleci in the available balance studies, expression of magnesium requirements for children is probably more accurate on the basis of intake per clay, rather than per unit of body weight or per amount of lean tissue.
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From page 212... ...
. In the one balance study in which children 7 to 9 years old were evaluated, positive magnesium balance was achieved on daily dietary magnesium intakes that ranged from 121 to 232 mg (~.0 to 9.7 mmol)
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From page 213... ...
, no significant differences were seen in the magnesium balances measured or in the percentage of magnesium absorbed (Sojka et al., 1997~. The calcium contents of the cliets provicleci in the other two balance studies of adolescents were 1,200 mg (30 mmol)
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From page 214... ...
214 V, oo o CS ¢ V, V, o ¢ · ~ V, · ~ V: _` A_ .= V, ~ o · 5 - _` o ~ o Ct ·5¢ = .
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From page 216... ...
/day. The median magnesium intake is 206 mg (8.6 mmol)
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From page 217... ...
(1996) study was not inclicateci, it is possible that one of the reasons that most of the girls were in positive magnesium balance on the 176 mg (7.3 mmol)
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From page 218... ...
Thus, the EAR is estimated to be 5.3 mg (0.22 mmol) /kg/day in 14- through 18-year-old boys and girls, given that the highest average level provided in any of the five long-term balance studies (Anclon et al., 1996; Greger et al., 1978, 1979; Schwartz et al., 1973, Sojka et al., 1997)
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From page 219... ...
/day Ages I 9 through 30 Years Indicators Used to Set the EAR for Men Balance Studies. The results of studies that have looked at magnesium balance in men and women age ci 19 through 30 years in various situations are inclucleci in Table 6-2.
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From page 221... ...
The average magnesium intake of this age group of women was 239 + 80 mg (10 + 3.3 mmol) ; this intake resulted in positive magnesium balance or equilibrium in three of the eight subjects.
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From page 222... ...
/clay. This EAR is also baseci on the assumption that the best current indicator of adequacy, given the lack of supporting ciata for other outcomes, is for an incliviclual to maintain total body magnesium over time as opposed to being in negative magnesium balance.
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From page 223... ...
, average magnesium balance was positive; but the magnesium intake was not sufficient on the high-fiber or high-oxalate cliets to maintain magnesium balance. Magnesium balance in male subjects age ci 19 to 64 years given lower magnesium intakes (229 or 258 mg t9.5 or 10.8 mmol]
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From page 224... ...
224 V, o o Get ¢ · ~ V, V: _` in_ · ~ V, Cry VO o u _` V)
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From page 226... ...
This EAR is also baseci on the assumption that the best current indicator of adequacy, given lack of supporting data for other outcomes, is for an incliviclual to maintain total body magnesium over time as opposed to being in negative magnesium balance. The observed change from average negative magnesium retention to positive retention or vice versa caused by changes in other factors in the diet (for example, fiber, protein)
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From page 227... ...
. EAR Summary: Ages 3 ~ through 50 Years, Women Baseci on the one stucly clescribeci above in which women aged 25 to 53 years were predominantly in negative magnesium balance at an average intake of 231 mg (9.6 mmol)
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From page 228... ...
. A positive magnesium balance was found in the men who consumed an average intake of 381 mg (15.9 mmol)
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From page 230... ...
. Because the data for the age group 31 through 50 years reflect more instances of negative balance when dietary magnesium intakes were in the range of 300 to 350 mg (12.5 to 14.6 mmol)
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From page 231... ...
Balance Studies. No magnesium balance studies that meet the criteria previously clescribeci have been reported in subjects over 70 years of age.
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From page 232... ...
The methods used in the studies of magnesium tolerance testing and intracellular magnesium cliscusseci above have yet to be validated sufficiently to serve as the basis for estimating average requirements. The reported magnesium intakes from the three available studies using these methodologies, however, are consistent with balance studies in younger age groups.
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From page 233... ...
found that in elderly subjects, an average clietary magnesium intake of 311 mg ~ 13.0 mmol) / clay was accompanied by a lower mean reci blood cell magnesium concentration, which was not found in younger controls.
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From page 234... ...
Therefore, serum magnesium concentrations do not appear to be adequate indicators of magnesium status. Intracellular Magnesium.
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From page 235... ...
The results of these studies are not consistent, possibly clue to the control groups that were used or the inability to distinguish whether altered magnesium status precedes the outcome or the outcome influences magnesium status. In one cross-sectional study, lower serum magnesium concentrations were observed in women cluring preform labor (n = 71)
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From page 237... ...
or with serum magnesium concentrations at approximately 30 weeks gestation; and in a small number of women with adverse outcomes, tissue concentrations of magnesium were not abnormal at the time of delivery (Skajaa et al., 1991~. A retrospective study by Conracit and coworkers (1984)
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From page 238... ...
. Daily magnesium intakes by pregnant women in the United States, where the study by Sibai and coworkers was completeci, ranged from 158 to 259 mg (6.6 to 10.8 mmol)
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From page 239... ...
Lower intracellular magnesium concentrations have been recently reporteci in women with
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From page 240... ...
Balance Studies. A magnesium balance study in six lactating women, six nonlactating postpartum women, and seven women who were never pregnant found lower urinary magnesium concentrations in lactating women compared with women who were never pregnant (Dengel et al., 1994~.
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From page 241... ...
Although this study found lower urinary magnesium excretion in lactating women consuming an estimated tinily average magnesium intake of 217 mg (9 mmol) , another study found no difference in urinary magnesium concentrations between lactating and never-pregnant women who consumed higher average tinily intakes of magnesium, around 270 mg (11.3 mmol)
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From page 242... ...
/day for lactating women ages 14 through 18 years. Special Considerations Mothers Nursing Multiple Infants.
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From page 243... ...
(Morcles and Wacker, 1978; Ranciall et al., 1964~. Hypermagnesemia resulting from impaired renal function anci/or intravenous administration of magnesium can result in more serious neurological and cardiac symptoms, but elevateci serum magnesium concentrations greater than 2 to 3.5 mmol/ liter (4.8 to 8.4 mg/cil)
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From page 244... ...
Gastrointestinal manifestations developed in ~ of 25 pregnant women being given 384 mg (16 mmol) of daily magnesium as magnesium chloride supplements for the prevention of preform delivery, although one patient receiving the placebo treatment also clevelopeci diarrhea (Ricci et al., 1991~.
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From page 245... ...
. Levels of fecal output of soluble magnesium and fecal magnesium concentration were elevated in individuals with diarrhea induced by 168 to 2,320 mg (7 to 97 mmol)
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From page 246... ...
of supplementary magnesium Infants: Ages OthroughI2 Months No specific toxicity ciata exist on which to establish a UL for infants, tocicilers, and children. The lack of any available ciata regarciing the effects of magnesium supplements in infants makes it impossible to establish a specific UL for infants.
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From page 247... ...
However, as noted above, magnesium levels obtained from food are insufficient to cause adverse reactions even in these inclivicluals. Patients with certain clinical conditions (for example, neonatal tetany, hyperuricemia, hyperlipiclemia, lithium toxicity, hyperthyroiclism, pancreatitis, hepatitis, phlebitis, coronary artery disease, arrhythmia, and digitalis intoxication tMorcles and Wacker, 1978]
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From page 248... ...
· Biochemical indicators that provide an accurate and specific marker(s) of magnesium status must be investigated in order to assess their ability to predict functional outcomes that indicate adequate magnesium status over prolonged periods.
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From page 249... ...
is neecleci. · Investigations are neecleci to assess the inter-relationships between clietary magnesium intakes, indicators of magnesium status, and possible health outcomes that may be affected by inadequate magnesium intakes, such as hypertension, hyperlipiclemia, atherosclerotic vascular disease, altered bone turnover, and osteoporosis.
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