Neal S. Parikh, MD

The Dietary Approaches to Stop Hypertension (DASH) diet is known reduce blood pressure in hypertensive and normotensive individuals. The authors assessed whether DASH diet adherence is associated with incident stroke.
The authors performed their analyses in two large, prospective Swedish cohorts of middle-aged to older men and women free of incident stroke.  The participants answered a 350-item questionnaire on diet and vascular risk factors in the late 1990s and were followed by linkage with the National Patient Register and the Cause of Death Register.
The exposure variable was a modified DASH diet score, assessed based on a validated food-frequency questionnaire. Covariates included standard demographics and vascular risk factors (hypertension, hyperlipidemia, diabetes, atrial fibrillation, smoking history, aspirin use, family history of myocardial infarction at early age, and body mass index).  Total caloric intake was included as a covariate, but dietary sodium was not. The outcome measure was incident stroke (ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage).  Participants were classified into quartiles based on their DASH diet score. Multivariate analyses were performed to test the association between DASH adherence and incident stroke.
Participants with high adherence to the DASH diet were fairly similar to participants with low adherence. The mean age was 60 years. Approximately 50% were overweight. Approximately 20% had hypertension, 10% had hyperlipidemia, and 6% had diabetes.  Over 882,727 person-years of follow-up, there were 3,896 ischemic strokes, 560 intracerebral hemorrhages, and 176 subarachnoid hemorrhages. High adherence to the DASH diet was associated with a lower risk of ischemic stroke and a trend towards lower risk of intracerebral hemorrhage. Participants in the highest quartile had a 14% lower risk of ischemic stroke than those in the lowest quartile.
This study adds to two prior studies that suggested that adherence to a DASH diet is associated with lower risk of stroke. The two prior studies and this study are likely underpowered for intracerebral hemorrhage and subarachnoid hemorrhage. The authors note that a similar association between the Mediterranean diet and stroke risk has been identified. Features shared by the DASH and Mediterranean diets may be responsible for lower stroke risk.  
The main limitations of this study are the observational design and the outdated cohort, which likely did not benefit from contemporary vascular risk factor management. However, in the context of prior studies, this study provides compelling evidence in support of a healthy diet for the prevention of stroke.