Lancet, vol. 340: August 22, 1992, p 483
Sir, The LIMIT-2 trial (June 27, p 1553) makes a most important contribution to a confused topic -- ie, the relevance of magnesium to ischaemic heart disease (IHD). This new evidence establishes the value of magnesium in the treatment of myocardial infarction. But what is its role in prevention before infarction? Magnesium has long been of interest in relation to IHD. One observation consistent with an aetiological role is reduced amounts in the myocardium of subjects whose deaths had been certified as due to heart disease, even when death had been "sudden". (1). The Caerphilly Heart Disease study of men aged 45-59 years at baseline (2, 3) has provided evidence that low dietary magnesium is predictive of IHD. 7-day weighed dietary records were kept by 665 men (4). Prevalent heart disease was identified by the London School of Hygiene and Tropical Medicine questionnaire and by electrocardiography, with standard criteria (5), and men were divided into those with symptomatic heart disease (previous myocardial infarction and/or current angina; 97 men) and those with no relevant symptoms (568 men). Incident heart disease events were identified during the following 5 years. These consisted of deaths certified as due to IHD (ICD 410-414) and non-fatal myocardial infarctions that fulfilled World Health Organisation criteria (6). Mean daily intakes of magnesium were:
No of Mean intake (SD) men (mg Mg/day) No symptomatic IHD at baseline No incident event 540 310 (105) An IHD event 28 274 (81) Symptomatic IHD at baseline No incident event 87 283 (91) An IHD event 1091) An IHD event 10 248 (86)
The mean daily intake of magnesium was about 12% lower in men who later had an IHD event, both in those with IHD at baseline and those without. Overall, the intake was lower by 38.9 mg (95% confidence interval [CI] 5.3-72.6 mg) in those who had an event, and adjustment for the presence or absence of baseline symptoms reduces this difference to 35.6 mg daily (95% CI 2.0-69.1).
MRC Epidemiology Unit (South Wales),
LLandough Hospital Penarth, South Glamorgan CF6 1XX, UK
1. Elwood PC, Sweetnam PM, Beasley WH, Jones D, France R. Magnesium and calcium in the myocardium: cause of death and area differences. Lancet 1980, ii: 720-22.
2. Caerphilly and Speedwell Collaborative Group. Caerphilly and Speedwell collaborative heart disease studies. J Epidemol Community Health 1984; 38: 259-62.
3. The Caerphilly Collaborative Heart Disease Stuties. Project description and manual of operations. Cardiff, MRC Epidemiology Unit, 1985.
4. Fehily A.M, Yarnell JWG, Butland BK. Diet and ischaemic heart disease in the Caerphilly study. Human Nutr Appl Nutr 1987; 41A: 319-26.
5. Bainton D, Baker IA, Sweetnam PM, Yarnell JWG, Elwood PC. Prevalence of ischaemic heart disease: the Caerphilly and Speedwell Surveys. Br Heart J 1988; 59; 201-06.
6. Yarnell JWG, Baker IA, Sweetnam PM, et al. Fibrinogen, viscosity, and white blood cell count are major risk factors for ischemic heart disease: the Caerphilly and Speedwell Collaborative Heart Disease Studies. Circulation; 83: 836-44.
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