The Calcium Controversy: A Cardiovascular Risk?
Ronald Steriti, ND, PhD
Two recent studies have shown that calcium supplementation (as monotherapy) was associated with increased cardiovascular risk. Magnesium and potassium may be the missing minerals needed for the prevention of disease.
A recent study has shown that calcium supplementation in healthy postmenopausal women is associated with an increase in cardiovascular event rates.1 A meta-analysis has also shown that calcium supplements (without coadministered vitamin D) are associated with an increased risk of myocardial infarction.2 A population-based, prospective study of Swedish men with relatively high intakes of dietary calcium and magnesium showed that calcium supplementation above the recommended daily intake may reduce all-cause mortality.3
Calcium with Vitamin D
Results from the Women’s Health Initiative showed that calcium and vitamin D supplementation neither increased nor decreased coronary or cerebrovascular risk in generally healthy postmenopausal women over a 7-year period.4,5
The Atherosclerosis Risk in Communities Study showed that dietary magnesium intake was marginally inversely associated with the incidence of ischemic stroke.6 A study of Finnish male smokers showed that a high magnesium intake may play a role in the primary prevention of cerebral infarction.7
In 2007, a small study showed that dietary magnesium deficiency induces heart rhythm changes, impairs glucose tolerance, and decreases serum cholesterol in postmenopausal women.8 A more recent Dutch study evaluating the association between tap water hardness, magnesium, and calcium concentration and mortality due to ischemic heart disease or stroke showed conflicting results. There was an inverse relationship between tap water magnesium intake and stroke mortality in men with the 20% lowest dietary magnesium intake (hazard ratio per 1 mg/L intake = 0.75; 95% confidence interval: 0.61-0.91), whereas the opposite was observed in women with the 20% lowest dietary magnesium intake.9
An article by Rowe, appearing in the American Journal of Cardiology, expounds on the association between the calcium:magnesium ratio and cardiovascular risk.10 Magnesium, which is “nature’s calcium blocker,” may precipitate a magnesium ion deficiency, ischemia, an increase in catecholamine levels, and insulin resistance, as well as a calcium overload of the myocardium, conditions conducive to myocardial infarction.10
Seelig has stressed that Finland, which has the highest calcium:magnesium intake ratio (well above the ideal calcium:magnesium ratio of 2:1), has the world’s highest cardiovascular morbidity and mortality rates.11
A high calcium:magnesium intake ratio interferes with magnesium absorption, increases the potential for clot formation with vasospasm, and increases oxidative stress, with the latter also more likely to occur as a result of the reduced effectiveness of magnesium as an antioxidant in the presence of catecholamine auto-oxidation.
An adequate total intake of calcium for adults is 1000 to 1200 mg QD; therefore, maintaining a favorable 2:1 ratio would require a daily total magnesium intake of 500 to 600 mg QD rather than “the recommended dietary allowance of 320 mg/day for adult women.”
Finally, it is noteworthy that magnesium, in addition to calcium, is necessary for bone structure and reduces the likelihood of osteoporosis; a calcium:magnesium intake ratio that is excessive will offset the effectiveness of magnesium in providing this function.12
Results of the Shanghai Women’s Health Study showed an inverse association between calcium and magnesium intake and type 2 diabetes risk.13 An interesting study of the calcium:magnesium ratio in local groundwater and the incidence of acute myocardial infarction among men in rural Finland showed a protective role of magnesium and a low calcium:magnesium ratio against coronary heart disease, but it did not support the earlier hypothesis of a protective role of calcium.14 A recent article proposed that a high serum calcium:magnesium ratio is more appropriate and that alterations in this ratio could lead to increased development of new and recurrent breast cancer.15
Magnesium is essential for DNA duplication and repair, and magnesium deficiency favors DNA mutations leading to carcinogenesis. Dietary intake of magnesium in the United States is less than the recommended amount, and the deficit is more pronounced in older individuals, in whom gastrointestinal and renal mechanisms for magnesium conservation are not as efficient. Furthermore, healthy postmenopausal women are frequently advised to take supplemental calcium, but not magnesium and vitamin D, to maintain bone structure and overall health.
Results of the Nurses’ Health Study showed that low calcium intake, and perhaps low potassium intake, may contribute to increased risk of ischemic stroke in middle-aged American women.16 Another study showed that diets rich in potassium, magnesium, and cereal fiber reduced the risk of stroke, particularly among hypertensive men.17
A Cochrane Database Review showed no robust evidence that supplements of any combination of potassium, magnesium, or calcium reduced mortality, morbidity, or hypertension in adults, although no study included all three minerals. Subjects taking a combination of potassium and magnesium had statistically nonsignificant reductions in both systolic blood pressure (mean difference = −4.6 mm Hg, 95% CI: −9.9 to 0.7) and diastolic blood pressure (mean difference = −3.8 mm Hg, 95% CI: −9.5 to 1.8) compared with control subjects, although the results were heterogeneous (I(2)[AM3] = 68% and 85% for systolic blood pressure and diastolic blood pressure, respectively).18
Ron Steriti, ND is a researcher for Dr. Jonathan V. Wright of the Tahoma Clinic and Meridian Valley Labs in Renton, WA. He is a graduate of Southwest College of Naturopathic Medicine and has a PhD in Electrical Engineering from the University of Massachusetts at Lowell.
1. Bolland, MJ, Barber PA, Doughty RN, et al. Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. BMJ. 2008;336:262-266. doi: 10.1136/bmj.39440.525752.BE.
2. Bolland MJ, Avenell A., Baron JA, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2008;341:c3691.
3. Kaluza J, Orsini N, Levitan EB, Brzozowska A, Roszkowski W, Wolk A. Dietary calcium and magnesium intake and mortality: a prospective study of men. Am J Epidemiol. 2010;171:801-807.doi:10.1093/aje/kwp467.
4. Hsia J, Heiss G, Ren H, et al. Calcium/vitamin D supplementation and cardiovascular events. Circulation. 2007;115:846-854.
5. LaCroix AZ, Kotchen J, Anderson G, et al. Calcium plus vitamin D supplementation and mortality in postmenopausal women: the Women’s Health Initiative calcium-vitamin D randomized controlled trial. J Gerontol A Biol Sci Med Sci. 2009;64:559-567.
6. Ohira T, Peacock JM, Iso H, Chambless LE, Rosamond WD, Folsom AR. Serum and dietary magnesium and risk of ischemic stroke: the Atherosclerosis Risk in Communities Study. Am J Epidemiol. 2009;169:1437-1444.
7. Larsson SC, Virtanen MJ, Mars M, et al. Magnesium, calcium, potassium, and sodium intakes and risk of stroke in male smokers. Arch Intern Med. 2008;168:459-465.
8. Nielsen FH, Milne DB, Klevay LM, Gallalgher S, Johnson L. Dietary magnesium deficiency induces heart rhythm changes, impairs glucose tolerance, and decreases serum cholesterol in post menopausal women. J Am Coll Nutr. 2007;26:121-132.
9. Leurs LJ, Schouten LJ, Goldbohm RA, van den Brandt PA. Relationship between tap water hardness, magnesium, and calcium concentration and mortality due to ischemic heart disease or stroke in The Netherlands. Environ Health Perspect. 2010;118:414-420.
10. Rowe WJ. Calcium-magnesium-ratio intake and cardiovascular risk. Am J Cardiol. 2006;98:140.
11. Seelig M. Cardiovascular consequences of magnesium deficiency and loss: pathogenesis, prevalence and manifestations–magnesium and chloride loss in refractory potassium repletion. Am J Cardiol. 1989;63:4G-21G.
12. Seelig MS. Interrelationship of magnesium and estrogen in cardiovascular and bone disorders, eclampsia, migraine and premenstrual syndrome. J Am Coll Nutr. 1993;12:442-458.
13. Villegas R, Gao RT, Dai Q, et al. Dietary calcium and magnesium intakes and the risk of type 2 diabetes: the Shanghai Women’s Health Study. Am J Clin Nutr. 2009;89:1059-1067.
14. Kousa A, Havulinna AS, Moltchanova E, et al. Calcium:magnesium ratio in local groundwater and incidence of acute myocardial infarction among males in rural Finland. Environ Health Perspect. 2006;114:730-734.
15. Sahmoun AE, Singh BB. Does a higher ratio of serum calcium to magnesium increase the risk for postmenopausal breast cancer? Med Hypotheses 2010;75:315-318.
16. Iso H, Stampfer MJ, Manson JE, et al. Prospective study of calcium, potassium, and magnesium intake and risk of stroke in women. Stroke. 1999;30:1772-1779.
17. Ascherio A, Rimm EB, Hernán MA, et al. Intake of potassium, magnesium, calcium, and fiber and risk of stroke among US men. Circulation. 1998;98:1198-1204.
18. Beyer FR, Dickinson HO, Nicolson D, Ford GA, Mason J. Combined calcium, magnesium and potassium supplementation for the management of primary hypertension in adults. Cochrane Database Syst Rev. 2006;3:CD004805.