Magnesium Research (1990) 3,3, 197-215 REVIEW ARTICLE
Summary: Prophylactic treatment of postmenopausal osteoporosis with oestrogen and calcium, often in combination, disregards the likelihood that an excess of each agent may increase magnesium requirements and decrease serum Mg levels. Relative or absolute Mg deficiency, which is likely in the Occident where the Mg intake is commonly marginal, can militate against optimal therapeutic bone response, Mg being important for normal bone structure, and can increase the risk of adverse effects. Although oestrogen has cardiovascular protective effects (expressed by the lower incidence of heart disease in premenopausal women than in men, and also in postmenopausal women given low dosage oestrogen replacement treatment), high dosage oestrogen oral contraceptives have caused increased intravascular blood clotting with resultant thromboembolic cardio- and cerebrovascular accidents. This might be contributed to by the oestrogen-mediated shift of circulating Mg to soft and hard tissues, which in persons with marginal Mg intakes may lead to suboptimal serum levels. If the commonly recommended dietary Ca/Mg ratio of 2/1 is exceeded (and it can reach as much as 4/l in countries with low to marginal Mg intakes), relative or absolute Mg deficiency may result, and this may increase the risk of intravascular coagulation, since blood clotting is enhanced by high Ca/Mg ratios. Mechanisms by which Ca activates the various steps in blood coagulation that are also stimulated by oestrogen are considered here, as are the multifaceted roles of Mg that favourably affect blood coagulation and fibrinolysis, through its activities in lipoprotein and prostanoid metabolism.
Key words: Alcoholic, bone structure, calcium therapy, Ca/Mg ratio, combination therapy, diabetic, intravascular coagulation, malabsorption, Mg deficiency, Mg lipoproteins, Mg requirements, oestrogen therapy, osteoporosis prophylaxis, postmenopausal, prostanoids.
Far less appreciated than calcium in the treatment or prevention of osteoporosis is the importance of magnesium. Osteoporotic bone has subnormal Mg content, such as is found in Mg deficiency. Many factors interact in the vulnerability to relative or absolute Mg deficiency of those prone to the development of osteoporosis. Low Mg intake, decreased Mg absorption, and hormonal changes that influence the distribution of magnesium and its effects on vitamin D metabolism are major factors in the elderly. In post-menopausal women, among whom are found most of the cases of osteoporosis, loss of oestrogen — which affects distribution of both Ca and Mg — is the predominant factor. The marginal Mg content of many Western diets can be contributory. Other conditions in which osteoporosis has developed, such as chronic alcoholism, disease- or therapy-induced Mg malabsorption or renal wasting, and poorly controlled diabetes mellitus increase Mg deficiency, the latter by increasing urinary Mg output and decreasing its tissue uptake. Since Mg deficiency causes changes in bone structure, the effect on Mg of agents used in prevention and treatment of osteoporosis should be considered. Oestrogen replacement delays onset and retards progression of postmenopausal osteoporosis, partly by antagonizing mobilization of both Ca and Mg by parathyroid hormone (PTH). The effect of oestrogen in lowering serum Mg by shifting Mg to soft tissues and bone could be implicated in the thromboembolic side effects of high doses of synthetic oestrogens. Since many of the steps in coagulation are Ca-dependent and are antagonized by Mg, might an increase in the serum Ca/Mg ratio in persons whose diets are low or marginal in Mg favour intravascular coagulation? Would adding Mg to oestrogen-Ca treatment of osteoporosis decrease that possibility?
Factors that increase magnesium inadequacy in those at risk of osteoporosis
Dietary magnesium deficiency
Mg intakes below the USA recommended daily allowance (RDA) of 300 mg/day are common1-12. Yet such an intake is below the recommendable daily intake of 6 mg/kg.day1,4,7-10. It has been customary to advise a dietary Ca/Mg ratio of 2/1, but with the frequently advised intake of 1200 mg/day of Ca or more for the elderly, the ratio may be at least 4/1. Excess of fat, sugar, phosphates, Ca, and vitamin D can each increase Mg requirements, and can lead to relative Mg deficiency1,4-7. The elderly, who are prone to involutional osteoporosis, often have reduced food intake13,14, impaired intestinal Mg absorption15,16, and increased urinary Mg excretion17 — factors that increase the likelihood of Mg deficiency. Their hormonal changes can contribute to Mg loss14 (Fig. 1).
Magnesium deficiency and decreased bone magnesium in
Markedly increased retention of Mg after a parenteral Mg load — one of the most reliable tests for Mg deficiency 9,18-20 has been found in postmenopausal patients with osteoporosis21,22. A study of Mg levels in serum and bone biopsy specimens of 10 elderly women (68.9 ± 6 years) with osteoporosis, compared with serum Mg of age-matched women free of bone disease and with necropsy bone of women who had died suddenly, showed marginally low serum Mg in the controls (1.74 mEq/litre) and low Mg (1.64 mEq/ litre) in the osteoporotic women23. The bone Mg of the osteoporotic women (1.54 ± 0.29 mg/g) was lower than that of sudden death victims (1.75 ± 0.25)23.
There was Mg malabsorption in 12 of 20 postmenopausal osteoporotics15. Loss of trabecular bone (in which the bone crystals are abnormal21,24) is associated with decreased trabecular bone Mg in postmenopausal and senile osteoporosis15,21,22,24, in alcohol-associated osteoporosis25, and in diabetics21,26. The abnormalities were not seen in oestrogen-treated women21. Patients with non-alcoholic cirrhosis (without osteoporosis) had low Mg in bone cortex rather than in trabecular bone.27
The acidity of bone extracellular fluid has been postulated to fall when Mg deficiency depresses the Mg-dependent ATPase H+-H+ pump in osteocytes.28 It is suggested that, as a result of lowered pH of the bone extracellular fluid, octacalcium phosphate formation in bone falls, although resorption proceeds — a possible way in which long term Mg deficiency may lead to osteoporosis28.
Conditions that increase magnesium needs, associated with
Magnesium malabsorption and renal wasting — Magnesium deficiency, manifested by low bone Mg and low bone Mg/Ca ratios, as well as by negative Mg balance, has been detected in patients with sprue, steatorrhea, inflammatory bowel disease, intestinal resections, and genetic isolated Mg malabsorption29-36. Malabsorption was associated with slight generalized bone thinning in a 67-year-old man with malabsorption32, and with evidence of demineralization in a black 56-year-old woman36. Vertebral osteoporosis was seen in a young man with Mg deficiency secondary to intestinal resection30. Juvenile osteoporosis has been reported in Barrter's syndrome, a genetic renal Mg wasting condition37. Mg malabsorption15 and renal Mg wasting38 have been diagnosed in postmenopausal osteoporosis.
Alcoholism — Alcoholics' poor food intake, and their malabsorption, in addition to the increase of urinary Mg output caused by, alcohol, even when consumed in moderate amounts39-41, can cause severe enough Mg deficiency to cause overt signs: Mg-responsive tremors, hallucinations, convulsions, and arrhythmias41-43. Chronic Mg deficiency of alcoholism9 may contribute to development of osteoporosis25.
Pregnancy — Pregnancy increases the need for both Mg and Ca, because of both fetal and maternal requirements5,44; osteoporosis can he a risk among women who have had multiple pregnancies. In such women, repeated drains on Mg, as well as on Ca, may contribute to hyperparathyroidism of pregnancy (see below) which is so common as to be termed 'physiological'5,45, and which mobilizes bone minerals,
Diabetes mellitus — Diabetes mellitus is a disease that is characterized by Mg depletion, caused by complex mechanisms9. The extent of the Mg loss in diabetics is related to the severity of the disease. Osteoporosis is not infrequent in insulin-dependent diabetics21,46. Severe hypomagnesaemia has long been associated with decompensated diabetes47. Less profound reductions in serum Mg have been demonstrated in juvenile diabetics48,49. Contributory to the Mg deficiency of diabetes mellitus is glycosuria, which increases Mg output in the urine even in normal subjects given glucose loads41-50. Insulin is important in cellular uptake of Mg51,52; in its long term inadequacy or with refractoriness to its activity, diminished tissue Mg — including that of bone — is likely.
Interrelations between magnesium and calcium
High calcium intake with marginal or low magnesium intake
To compensate for the loss of Ca from osteoporotic bone, oral treatment with Ca and vitamin D as a calcaemic agent is common, without taking into consideration the effect of these agents on Mg requirements, or the importance of Mg in maintaining normal bone matrix5. High dietary Ca/Mg ratios interfere with Mg absorption, partially because Ca and Mg share a common intestinal absorption pathway34,53,54. Vitamin D favours Ca over Mg absorption55. Metabolic studies have shown interference by high dietary Ca with Mg retention of normal young women1, and of patients with osteopathies (Fig. 2)34,56,57. Moderately high Ca intake (1270 to 2360 mg/day) had little effect on the Mg balance of elderly men58. Similarly, addition of 900 mg Ca/day to young men's diets containing 700 mg Ca had little effect on Mg balance59. However, even though the Mg balance was not affected by up to 2 g/day of Ca in normal young men, their plasma Mg levels fell60.
Effect of magnesium supplementation on hypocalcaemia
Persons subject to osteoporosis who have low Mg dietary intakes are prone to low serum levels of both cations. Raising Mg intake increases Ca absorption in normal young men on adequate Ca intake61. The restoration by parenteral or oral Mg treatment of responsiveness to vitamin D and parathyroid hormone (PTH) (see below) is important in Mg-deficient patients. It corrects hypocalcaemia as well as hypomagnesaemia31,33,55.
Interrelation of magnesium with parathyroid hormone — Low Ca levels, despite adequate dietary Ca, may result from Mg deficiency, as well as from Ca deficiency. It has long been known that hypocalcaemia can be a manifestation of severe Mg deficiency in adults30-33,47,62,63, as well as in infants30-33,47,62,63, with convulsive hypocalcaemia responsive to Mg but not to Ca5,64,65. Their refractoriness to calcaemic therapy is caused by impaired release of PTH and target organ (bone and kidneys) resistance to PTH66-71. However, early or less severe Mg deficiency increases PTH secretion, which increases bone mineral mobilization not only of Ca but of Mg in vitro68 and in vivo in humans36,63,69. Studies of adults with hypocalcaemia secondary to Mg deficiency showed that most had both impaired PTH secretion and end organ resistance to PTH69-71. Mg is required for activity of adenylate cyclase in parathyroid tissue72, in kidney73, and in bone74. That enzyme converts ATP to cyclic AMP (cAMP)75, which is needed for PTH secretion69. Defective cAMP generation may thus be responsible for both target organ resistance to PTH and for its impaired secretion in severe Mg deficiency69-71.
Vitamin D interrelations with magnesium — Vitamin D deficiency impairs not only Ca absorption, but that of Mg53,76,77. Formation of the active hormonal metabolites of vitamin D partially depends on enzymes that are Mg-dependent78,79. Thus the Mg status affects the calcaemic response to vitamin D treatment of osteoporotic patients. Hypocalcaemic patients with Mg deficiency have not reresponded to the addition of vitamin D to Ca therapy in refractory hypoparathyroidism80, in malabsorption or alcoholism81, or in refractory rickets82-24 until Mg was provided. It is important to note that the provision of excess Ca or vitamin D and phosphate without correction of a Mg deficit can cause bone to be hypermineralized and brittle5. The effect of acute Mg deficiency on production of the active vitamin D metabolites is inconsistent, possibly due to the biphasic effect of Mg on the 1-α-hydroxylase activity85,86. Both normal and low lelevels of the vitamin D metabolites have been found in Mg-deficient patients treated with vitamin D87,88. Prolonged (up to 20 days) Mg administration, sufficient to raise the level of PTH (t(the trophic hormone for a-hydroxylation), has raised low levels of calcitriol and serum Ca88.
The significance of interrelations between vitamin D and Mg as regards bone disease requires further study. An important effect of meeting the increased Mg requirement of baby pigs treated with high dosage vitamin D was that of significantly increasing bone elasticity, which resulted in some increased resistance to breakage76 (Fig. 3).
Interrelations of oestrogen with PTH, vitamin D, and magnesium
Oestrogen treatment; antagonism of PTH
Prolonged replacement oestrogen therapy, preferably with low dose conjugated oestrogens (Premarin), alternating with a progestin, is useful in prophylactic and therapeutic treatment of postmenopausal osteoporosis — whether associated with spontaneous or iatrogenic cessation of oestrogen secretion89-98. Inferential evidence that hyperparathyroidism is a factor in postmenopausal osteoporosis is its increased frequency at and after the menopause99,100, and its greater severity in hyper- than in hypoparathyroid women101. Oestrogen antagonizes PTH-induced bone resorption in vitro102,103, and bone of ovariectomized rats is more sensitive to PTH — as measured by Ca and hydroxyproline content and decreased bone thickness104. Loss of oestrogen at menopause causes negative Ca balance, and greater bone responsiveness to the Ca-mobilizing effect of PTH, and decreased formation of calcitriol105. These findings, and the evidence that oestrogen inhibits the bone-resorbing effect of PTH101,106, support the clinical use of oestrogen in osteoporosis. It is possible that the loss of the protective effect of oestrogen on bone — mediated both by its effects on PTH release and PTH-induced demineralization — is the cause of postmenopausal osteoporosis. Both of these effects may be influenced by the effects of oestrogen on Mg5,107.
Oestrogen effect on vitamin D metabolism — role of
The evidence, from metabolic balance studies, that young women retain Mg better on marginal Mg intakes than do young men has suggested that the effect of oestrogen on Mg might contribute to their greater resistance to arterial and cardiac disease1,4,5,107. There are some data indicating shift of blood Mg to tissues under the influence of oestrogen: soft tissue108,113 and bone114-116 (Table 1). Circulating Mg levels are higher in young men than in young women, particularly when oestrogen levels are highest, such as during ovulation or during oral contraceptive use115-128, and when pregnant (see below). Oestrogen-induced lowering of serum Mg is not associated with increased urinary Mg output or decreased Mg absorption, which supports the premise that oestrogen shifts Mg to tissues. After the menopause, women lose more Mg in their urine than do young women, whether or not they are taking oral contraceptives126-128(Fig. 4). Oestrogen/progestogen treatment can reduce Mg loss and may thereby be beneficial in postmenopausal osteoporosis127-129.
Even when corrected for haemodilution, serum Mg is lower in pregnant than in non-pregnant women5,130-132. During pregnancy, meeting fetal Mg needs is the major factor in predisposing to maternal Mg deficiency, but the high oestrogen levels probably contribute to the fall in serum Mg early in pregnancy. Magnesium deficiency has been implicated in the pathogenesis of pre-eclampsia5,44,134-138, in part through increased blood coagulation135-138.
Oestrogen effect on vitamin D metabolism — role of magnesium
Low calcitriol levels, and low activity of enzymes involved in its formation, are associated with old age and with involutional osteoporosis139-144, but the response of the disease to its administration is inconsistent143. The need for more parathyroid stimulation for normal vitamin D metabolism by women with osteoporosis, and the lesser response of the elderly to calcitriol144, has been correlated with possible Mg deficiency145. The level of calcitriol has been raised during physiologically increased oestrogen, for example during pregnancy146, and during use of oestrogen147. It has been suggested that impaired activation of 1-α-hydroxylase might be responsible for the oestrogen deficiency-induced decreased formation of the active vitamin D metabolite148. On the grounds that low levels of the active form of vitamin D were found in Mg deficiency87, and that oestrogen increases Mg retention (see above), it is suggested that the increase in calcitriol formation caused by oestrogen might mediated by increased tissue Mg.
Worth exploring is the relationship to osteoporosis of the lower serum Mg and decreased urinary Mg loss by women on oestrogen therapy in comparison with those not so treated. Does this reflect a shift to bone, as in rats113-116? Does increased urinary Mg of postmenopausal women reflect their inability to retain Mg? It has been noted that low trabecular bone Mg, and abnormal bone crystals, seen in pelvic crest biopsies of osteoporotic patients are not present in post-menopausal women receiving oestrogen21.
Magnesium deficiency-associated thromboses; mechanisms
Magnesium/calcium in blood coagulation
That Ca activates blood clotting, and that Mg antagonizes this effect, has been known since 1944; it was assumed to result from competitive inhibition by Mg of Ca-dependent conversion of prothrombin to thrombin149. Since then, the need for Ca by many steps leading to fibrin formation and polymerization in clot formation150,151 has been further defined. Review of published evidence on counteraction by Mg of Ca-stimulated steps in coagulation focused on the effect of Mg on prothrombin and Factors V, VII, and IX, as well as on its enhancement of fibrinolysis152 (Table 2). Mg stabilizes fibrinogen and decreases fibrin formation; it also increases fibrinolysis159. Mg also slows thrombin generation, both in vitro and in vivo152,153.
Platelet aggregation requires both Mg and Ca, but is largely Ca-dependent. In vitro studies have yielded conflicting results as to the effect of Mg on platelet structure and function; at low, but not at higher than physiological concentrations, the Ca/Mg ratio is an important determinant154,155. When Ca was missing or low in concentration, Mg inhibited aggregation151,155-161. Addition of Mg to blood samples has reduced ADP-induced platelet clumping. It has been suggested that Ca is required for aggregation and Mg is required to maintain the shape of platelets and for deaggregation. Serotonin, the release of which from aggregating platelets is dependent on Ca and inhibited by Mg162-164, accelerates divalent cation-induced platelet clumping165. Mg is released from platelet granules165; it inhibits both further platelet release reactions154 and steps in blood coagulation (Table 2) by competitive inhibition of Ca. Mg deficiency increases serotonin release from platelets166,167. Serotonin-induced vascular muscle contraction is also inhibited by Mg168,169.
Experimental magnesium deficiency
Partial thromboplastin and thrombin clotting times were significantly shortened in Mg-deficient calves, but their prothrombin time, their platelet counts, and platelet aggregation were unaffected170. Hypercoagulability of blood of Mg-deficient rats, produced by feeding diets rich in saturated fat to animals (see below), decreased coagulation time and increased prothrombin consumption and could be prevented by adding Mg to the diet171,172.
Prostacyclin and thromboxane — There is some evidence that Mg deficiency inhibits synthesis of prostacyclin (a vasodilating, anti-platelet-aggregating, anti-hypertensive prostaglandin173-176), and increases release of thromboxane A2 and B2 (TXB2), which are vasoconstrictive, pro-aggregating prostaglandins175-176 from platelet aggregates. It has been hypothesized that the accelerated platelet clumping produced by platelet-active collagen (as a model of the bared subendothelial collagen of damaged vascular intima) in Mg-deficient lambs was mediated by diminished production of prostacyclin177.
The release of increased amounts of arachidonic acid, the precursor of prostanoids, from thymocytes of Mg-deficient rats178 led to study of the effect of Mg deficiency on these derivatives of phospholipid metabolism in blood179. Prostacyclin, as measured by its stable metabolite 6-keto-PGFa1, was increased two-fold; PgE2 was increased threefold, but TXB2 was increased more than 10-fold. These increases were attributed to increased Ca levels in Mg-deficient rats, since the enzyme responsible for liberation of arachidonic acid is Ca-activated phospholipase A2180. The depression of cyclic AMP seen in Mg deficiency may also participate directly in the markedly increased TXB2 synthesis of Mg deficiency, since cyclic AMP inhibits TXB2 production by platelets181. Fatty acid metabolism is altered in Mg deficiency182-188, with arachidonic acid production diminished as a result of slowed conversion of linoleic acid to arachidonic acid188,189, a finding pertinent to the role of prostanoids in blood coagulation.
Dietary Mg depletion of humans has recently been shown to increase platelet aggregation and TXB2 release, effects that were reversed by Mg infusion189. A nine-fold increase in serum TXB2 was seen in a marathon runner immediately after racing, when his serum Mg was lowest (1.07 mEq/litre), as compared with the pre-race value190.
Interrelations of fat intake, hyperlipaemia and coagulability — High fat intakes, in experimental Mg deficiency, increases Mg requirements, as expressed by the anti-coagulative and cardiovasculo-protective effects of adding Mg to thrombogenic, hyperlipidaemic, or infarctoid diets3,5,6,171,172,191-207. Experimental Mg deficiency has long been known to affect serum lipoproteins191-199. Mechanisms involved in Mg/lipid interrelations, as they affect coagulation and vascular disease, are being elucidated182-187. Mg deficiency of weanling rats has caused hypertriglyceridaemia with increases in very low density lipoproteins (VLDL), and low density lipoprotein (LDL) fractions, with increased cholesterol in those fractions, but decreased cholesterol in the high density lipoproteins (HDL)182,l84-l87,202-204 (Fig. 5). Defective triglyceride removal from the blood in Mg-deficient rats183 is associated with reduction of plasma lecithin cholesteryl acyl-transferase (Fig. 6), and of lipoprotein1ipase203-206.
Magnesium deficiency-associated thromboses; clinical aspects and treatment
Marginal clinical magnesium deficiency
Patients with latent tetany of marginal Mg deficiency have developed thromboses and emboli; new events were prevented by Mg supplements, and recurred when supplements were discontinued122,207-211.
Postoperative; magnesium anaesthetics
An early study showed that blood taken from surgical patients, who had been anaesthetized with an Mg-containing preparation, clotted but then liquefied completely within 2 hours; blood of such patients at autopsy 12 hours after death was liquid212,213. Because there were no cases of phlebothrombosis or emboli among 120 survivors of major surgery so anaesthetized, the investigator undertook clinical trials of the presumed thrombolytic effect of Mg. Patients with deep vein phlebothrombosis responded to parenteral Mg therapy; oral Mg therapy was prescribed prophylactically, with resultant decreased platelet aggregation and inconsistent thrombolysis. In a confirmatory study of the improved recovery of patients with thrombophlebitis or phlebothrombosis, treated with intramuscular or oral Mg (providing 80 mg/ampoule and 50 mg/tablet), blood coagulation indices (clot formation, prothrombin times, antithrombin) were unaffected, but fibrinolysis increased substantially214.
Pregnancy-associated thrombotic disease
Pregnancy and puerperium — Pulmonary embolism is a major cause of death during pregnancy and the puerperium215, which suggests that the naturally high oestrogen secretion at that time increases intravascular coagulation. Comparison of incidence of postpartum phlebothrombosis treated with parenteral Mg, followed by oral Mg (200 mg three times/day for 3-10 days postpartum), provided after delivery, was compared with the phlebitic events during a prior year in which that regimen was not followed. Those treated with Mg exhibited substantial reduction in postpartum thrombosis, after spontaneous or operative delivery (Table 5)216.
Pre-eclampsia and eclampsia — Hypercoagulability of blood has been associated with pre-eclampsia and eclampsia, and with associated placental abnormalities5,134-138,217-219. Abnormalities that increase the risk of thrombosis in eclampsia include decreased plasminogen activation and decreased fibrinolysis, with resultant decreased thrombolytic potential. Also found were lowered platelet counts — which suggests their consumption as a result of intravascular coagulation218. (See above for interaction with prostanoids.)
Parenteral magnesium treatment of eclampsia; anticoagulant effect — Hypomagnesaemia, which is characteristic of pre-eclampsia and eclampsia before renal failure, is associated with comparable increases in coagulation (see above). Administration of pharmacological amounts of Mg is the time-honoured means of treatment of eclamptic convulsions and hypertension5,220,221. It is used as a drug, but much of it is retained134,220 — suggesting repair of underlying Mg deficiency. That the effect of Mg in eclampsia may also entail its antithrombotic effect was postulated on the basis of the rapid reduction of markedly increased platelet adhesiveness after intramuscular Mg in eclamptic women, and the combination of many factors that predispose to Mg deficiency in pregnancy135-138. When Mg deficiency produced eclampsia with glomerular microthrombi and decreased lowered platelet counts in pregnant ewes, the theory was extended to encompass the lowered prostacyclin/TXB2 ratio seen both with pregnancy and Mg deficiency137,138 (Fig. 7).
A decreased prostacyclin/TXB2 ratio has been implicated in the pathogenesis of toxaemias of pregnancy222. The relationship of the Mg deficiency of eclampsia to this change in prostanoids was suggested soon thereafter138,223,224. The inhibitory effect of Mg on both platelet aggregation and hypertension in toxaemias of pregnancy has been attributed to its stimulation of prostacyclin production223. That the anti-hypertensive effect of Mg might be mediated by prostacyclin was suggested by the increase in prostacyclin production induced by Mg infusion of normal subjects225.
Migraine, oestrogen and prostacyclin/TBX2 — Of particular interest as regards interrelations of oestrogen with Mg is the strong association of migraine with eclampsia1136,226,227; eclampsia was 220 times more prevalent in pre-eclamptics with histories of migraine than in those without. Migraine was found 2.5 times as often in patients with pre-eclampsia before the 34th week of pregnancy as it was in those with normal pregnancy228. Favourable results have been reported in 80% of 3000 women given 200 mg/day of Mg for the prophylaxis of eclampsia and migraine when they were taking oral contraceptives or were pregnant136,226.
Support for the premise that Mg deficiency is involved in the pathogenesis of migraine derives from its higher incidence among those prone to hypomagnesaemia, and relates it with association of the effect of Mg on prostanoids and thrombogenesis136,226,229 (Fig.7). Several specific interrelationships of vascular factors that seem to be involved in migraine230 that pertain to Mg deserve mention. Prostaglandin metabolism has been correlated with migraine (see above for Mg and prostanoids). Increased serotonin release from platelets231, which occurs in migraine232 may contribute to cerebral vasospasm; it is enhanced by Ca and inhibited by Mg162-165. Ca channel blockers are effective in prophylaxis of migraine233; Mg has been proposed as a physiological Ca channel blocker234, on which basis Mg treatment was proposed for migraine235.
Myocardial infarction, coronary artery disease; cerebral
Blood coagulation, fat intake, hyperlipaemia, and magnesium requirements — Increased platelet adhesiveness has long been recognized in ischaemic heart disease236, and is known to be intensified by hyperlipaemia due to high intake of saturated fatty acids237-240 and that found in clinical arteriothrombotic disease241.
Magnesium treatment in ischaemic heart disease; effects on lipoproteins — Reported as long ago as the adverse effects of saturated fats on blood coagulation in patients with ischaemic heart disease was the favourable response to (uncontrolled) Mg treatment of several hundred patients with ischaemic heart disease (IHD), with and without recent myocardial infarction242,243. Their reduction in angina, in association with lowered serum β-lipoproteins, persisted as long as the Mg treatment was maintained, but rose when it was discontinued. Clinical confirmation was provided in another series of patients, who experienced clinical improvement on similar treatment with MgSO4 (2 ml 50%,, intramuscularly every 5 d for 12 injections): marked reduction β-lipoproteins occurred, with no change in α-lipoproteins244,245(Table 6).
Effects on coagulation and fibrinolysis of magnesium treatment of ischaemic heart disease — In the foregoing uncontrolled study of the anti-anginal efficacy AMg, and the lowering of β-lipoproteins of patients with ischaemic heart disease by intramuscular Mg, it was found that Mg markedly reduced the increased plasmin inhibition, and functioned synergistically with heparin in management of patients who had suffered recent myocardial infarction244,245. In another study, platelet adhesiveness was studied in 25 patients within 48 h of myocardial infarction and was found to be markedly increased; their mean serum Mg on the third day was marginally low (1.7 mEq/litre), versus a control nor mal mean of 2.36 (Table 7)245. There is increasing clinical evidence that Mg deficiency predisposes to clinical cardiovascular disease, including myocardial infarction5,20,247-254 and that Mg treatment improves the post-infarction course by reducing risk of arrhythmias5,234,249,250-252,255-263.
Increasing serum Mg only to 2.1 mEq before partial occlusion (by suture) of coronary arteries of animals markedly diminished platelet aggregation at the site of injury and distal to it264. This suggests that Mg treatment in ischaemic heart disease might protect against thrombosis formation on atherosclerotic arteries and microthrombi associated with arteriospasms264. The anti-arrhythmic effect of Mg is implicated in the improved survival of post-myocardial infarction patients treated with Mg infusions; its anti thrombotic effect may also participate.
Cardiovascular protection by oestrogen
The lower cardiovascular disease death rate in pre menopausal women than in men suggests that oestrogen has a protective effect. It is proposed that this effect might be mediated by the improvement in Mg retention caused by oestrogen1,3,5,107. Experimental animals treated with oestrogen265,266, and pregnant animals with high oestrogen levels, have increased resistance to induced arterial and cardiac damage267-269. Epidemiological studies showing either no effect on270 or lowered coronary disease risk of elderly women receiving replacement low dosage oestrogens271-275 support the premise that oestrogen is protective against cardiovascular lesions.
Thrombophlebitis on high dose synthetic oestrogens — However, high levels of oestrogen have been reported to have been associated with intravascular coagulation5. Men treated with oestrogens for prostatic carcinoma had more thrombosis-associated cardiac disease than those not so treated276, although the degree of atherosclerosis seems not to have been affected277. The venous thrombophlebitic events in women on high dosage oestrogen-containing oral contraceptives278-280 (Fig. 8), and in women given oestrogens to inhibit lactation281,282, led to study of the increased coagulation caused by oestrogens. The synthetic oestrogens, especially in high doses, but not the conjugated oestrogens (in lower doses), shorten prothrombin time283, increase prothrombin consumption284, and increase platelet adhesiveness284,285. In low doses they exert little or no effect286. Premarin showed no significant increase of clotting tendency in women given 1.25 mg/d for a month287. An epidemiological study has shown no increased risk of stroke in postmenopausal women on low dose replacement oestrogen288.
High dose oestrogen-induced thrombophlebitis; due to lower ed serum magnesium? — It has been hypothesized that high dose oestrogens increase the risk of thromboembolism and phlebothrombosis as a result of oestrogen induced shift of circulating Mg to tissues, lowering serum Mg levels115,289. The recent report that oral contraceptive users who smoke have increased plate let aggregation and decreased prostacyclin levels290, and the interrelationships of Mg with prostacyclins (see above), provide more insight into additional mechanisms by which oestrogen may affect blood coagulation through its effects on Mg. It has been advised that during any long term oestrogen therapy the Mg status should be monitored and deficits corrected to reduce the risk of phlebothrombosis9,122,211.
This correlation of multiple interrelations among the factors that increase the likelihood of development of osteoporosis, and among the treatments of that disease (that currently emphasize administration of oestrogen and Ca), calls attention to the mechanisms by which such combination therapy may increase Mg requirements. Patients who take enough Ca supplements to exceed the commonly recommended Ca/Mg ratio of 2/I, especially in those with the marginal Mg dietary intake that is common in the developed world, may develop relative or absolute Mg deficiency, with suboptimal serum Mg levels. Combined Ca and oestrogen treatment of such patients might lower serum Mg, thereby increasing the risk of intravascular coagulation. Postmenopausal women who are treated with low dose replacement oestrogen to prevent or slow osteoporosis are not considered to be at risk of thromboembolic events such as have been associated with use of high dosage synthetic oestrogens. Ca activates many steps in blood coagulation; Ca supple mentation, in conjunction with oestrogen, might con tribute to an increased possibility of intravascular blood clotting. Mg counteracts some of the Ca- activated steps in blood coagulation, and even has some fibrinolytic activity. Furthermore, it has been shown to participate in activities that may function to correct the lipid and prostanoid abnormalities associated with Mg deficiency and that increase the risk of thrombosis. Thus Mg supplementation is suggested to reduce the risk of intravascular coagulation, and possibly to improve the anti-osteoporotic therapeutic effect.
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