The relationship between dietary magnesium intake, stroke and its major risk factors, blood pressure and cholesterol, in the EPIC-Norfolk cohort☆
Introduction
Stroke accounts for more than 5.5 million deaths annually and by 2020 predictions estimate that the global burden of stroke will account for 61 million disability-adjusted life years [1].
Elevated BP2 is a significant modifiable risk factor for stroke with an approximate fourfold increase in stroke risk in hypertensive individuals compared with the normotensive population [2]. Although established evidence indicates that elevated BP, hypertension and circulating cholesterol can be modified by dietary intake including: salt, alcohol, saturated fat and cholesterol [2] other dietary components, including magnesium, which is abundantly available in nuts, green leafy vegetables and whole grains, have been less extensively studied.
Magnesium has a number of metabolic roles in the body and may influence BP and blood lipids through different mechanisms [3], [4]. Magnesium may serve as a natural calcium channel blocker, exhibit beneficial effects on platelet coagulation, have a potential role in vasodilation and has been associated with reduced coronary artery calcification [4], [5]. Other proposed mechanisms include increased peroxidation of lipoproteins with subsequent acceleration of atherosclerotic plaque formation and low magnesium may facilitate an increase in inflammation which is associated with negative changes in lipid profile [3], [4]. Higher magnesium intake has been associated with lower risk of Type II diabetes [6], metabolic syndrome [7] and cardiovascular disease (CVD) [8].
Two recent meta-analyses have investigated the effects of dietary magnesium on stroke risk and CVD risk respectively [8], [9] showing inconsistent findings. The reason for these inconsistencies may be due to estimation of magnesium intakes from less precise methods of recording diet such as Food Frequency Questionnaires (FFQs) and 24 hour recalls. However, it has been increasingly suggested that the detailed 7-day diary represents dietary intakes more precisely [10].
Therefore, the purpose of this study was to determine whether dietary magnesium intake, estimated using a 7-day diary, was associated with BP, lipid profile and stroke risk in an adult general population of 4443 (representative of larger cohort 25,639) men and women.
Section snippets
Study population
The present study population is comprised of a randomly selected representative sample (n = 4000) of the EPIC-Norfolk cohort (n ~ 25,639), which will herein be referred to as EPIC-Norfolk sub-cohort. EPIC-Norfolk has previously been described in detail and the characteristics of the sample were comparable with other representative UK populations with the exception of a lower proportion of current smokers [10]. Ethical approval for the study was obtained from the Norwich Ethics Committee, and
Results
In the 4443 participants included in these analyses 45.0% were male, with an age range of 39–78 years. Mean BP was 140/85 (SD 18.5/11.5) and 136/82 (SD 19.5/11.4) mm Hg for males and females respectively (Table 1). There was a total of 928 incident strokes during follow-up (mean 9.58 years; total person years 42,556.5) between 1993 and 2008.
Men had significantly higher SBP, DBP and BMI and women had significantly higher TC levels (P for all < 0.001), and BMI (P = 0.01), but not family history of
Discussion
The main findings of this case–cohort study of British adults suggest that, after adjustment for several important confounding factors including age, smoking status, history of CVD, medication use, total energy intake and other dietary variables, there was a strongly significant association (P ≤ 0.01) between dietary magnesium intake and SBP and DBP in men, but not in women. There was also an association with TC in both men and women (P = 0.001 and P ≤ 0.01 respectively) which was attenuated but
Author contributions
Contribution of each author: The research question was formulated by AAW, PKM and LKMB who also analysed the data and wrote the manuscript. KTK and NJW are principal investigators of the EPIC-Norfolk. The data collection was organised by AAW, RNL. RNL performed the record linkage. MAHL obtained data from both food and supplement sources using the 7-day diet diaries. All authors contributed to the manuscript and commented on the final version.