Magnesium plays a role in several integral processes in the human body. Researches have sought to draw associations between magnesium levels and stroke in the past, most notably in the Atherosclerosis Risk in Communities (ARIC) study, concluding that low magnesium levels could be associated with the risk of ischemic stroke potentially through the effects of hypertension and diabetes. This Nurses’ Health Study (NHS) sought to further investigate this relationship by carrying out a nested case control study of ischemic stroke among 32,826 women who provided blood samples in 1989 and 1990. Strokes were confirmed according to the criteria of the National Survey of Stroke consisting mainly of sudden or rapid onset of neurologic deficits lasting more than twenty-four hours and, thereafter, incident ischemic strokes were matched 1:1 to controls who were free of stroke.

A total of 459 confirmed stroke cases and 459 controls had magnesium levels for analyses and this was divided into two main groups to differentiate between what can be considered “low” levels and normal levels as follows- (<0.82 mmol/l versus >0.82 mmol/l). Magnesium levels were measured by colorimetric assay on Hitachi 917 analyzer and tests of significance were conducted using Mantel-Haenszel and Fisher’s exact tests. With regards to the association between plasma magnesium and the risk of total ischemic stroke, the relative risk and 95% confidence interval for the lowest quintile compared to the highest quintile was 1.34 (0.86-2.10), p-trend 0.13. Women in the lowest quintile of plasma magnesium were most likely to be current smokers, use thiazide diuretics, post-menopausal hormone therapy, have hypertension and diabetes, and consume more alcohol  with median plasma magnesium levels in the lowest and highest quintiles being 0.78 mmol/l and 0.95 mmol/l respectively. Of note, the median magnesium levels (0.86 mmol/l) did not differ between ischemic stroke cases and controls.
 It was concluded that plasma magnesium levels were not associated with the risk of ischemic stroke in women across the full distribution of plasma magnesium, but that women in the lower quintile group had higher risk of ischemic stroke and this association remained unchanged after controlling for other factors associated with magnesium levels and stroke risk.