Vegetarian diet and stroke

Maintaining a healthy plant-based diet is associated with a lower risk for both total stroke and ischemic stroke, results from a study of three large cohorts suggest.

In this new study, the investigators developed three versions of plant-based diet indices to assess the quality of plant-based dietary intake without excluding all animal foods and examined the quality of plant-based diet in relation to stroke risk.

The study was published online March 10 in Neurology.

Research suggests that plant-based diets reduce the risk for cardiovascular disease, but few studies have examined the effect of these diets on the risk for stroke. Moreover, published research on this question has yielded conflicting results, the researchers note. Two previous investigations showed no association between a vegetarian diet and risk for stroke mortality, but one study found that vegetarian patients were at increased risk for total and hemorrhagic stroke.

For their study, the researchers analyzed data from three large American cohorts. Two, the Nurses' Health Study (NHS) and the NHS II, included only women. The third, the Health Professionals Follow-Up Study (HPFS), included only men. Among exclusion criteria were history of cardiovascular disease or cancer at baseline, missing dietary data, and implausible intake of dietary energy.

Participants in the three studies responded to questionnaires every 2 years, which provided information on lifestyle factors and medical history. Every 2 to 4 years, participants filled out a food frequency questionnaire.

To examine the populations' intake of plant-based foods, the investigators created a plant-based diet index (PDI), a healthful plant-based diet index (hPDI), and an unhealthful plant-based diet index (uPDI). They cited foods containing refined grains and added sugars as examples of unhealthful plant-based foods.

The researchers classified patients as vegetarian if they ate plant foods or other animal foods such as butter, dairy, or eggs but ate less than one serving per month of meat or fish. Other participants were considered nonvegetarians.

The analysis included 73,890 women in the NHS, 92,352 women in the NHS II, and 43,266 men in the HPFS. In each cohort, participants with the highest PDI had lower BMI, engaged in more physical activity, were less likely to smoke, had higher healthy and lower unhealthy plant food consumption, and had lower animal food consumption compared with participants with the lowest PDI scores.

For participants in the highest PDI quintile, the hazard ratio (HR) for total stroke was lower compared to that of participants in the lowest quintile (HR, 0.94). Participants with the highest hPDI had a significantly lower risk for total stroke (HR, 0.90) than those with the lowest hPDI. Those with the highest uPDI had a slightly higher risk for total stroke than those with the lowest uPDI (HR, 1.05).

With regard to ischemic stroke, for participants with the highest PDI, the HR was 1.04, compared to those with the lowest PDI. For participants with the highest hPDI, the HR was 0.92, and for those with the highest uPDI, the HR was 0.96.

There was no association between PDI and risk for hemorrhagic stroke.