The study researchers, who tracked the diets of nearly 75,000 men and women over 10 years, found that those who ate the most low-fat dairy foods and beverages were 12% less likely to have a stroke than those who ate the least.
"The most plausible explanation is that low-fat dairy food lowers blood pressure," says researcher Susanna Larsson, PhD, an associate professor of nutritional epidemiology at the Karolinska Institutet in Stockholm. "High blood pressure is a strong risk factor for stroke."
Previous research suggests that adequate vitamin D levels may help prevent development of high blood pressure.
Larsson says that nonfat dairy products such as skim milk likely have the same stroke-reducing properties as long as they are fortified with vitamin D.
In 1997, the study participants, who ranged in age from 45 to 83, answered a lengthy questionnaire that covered many aspects of their lifestyle and personal characteristics, including diet, exercise habits, body mass index, work, education, and medical history. At the time they enrolled in the study, none of them had had any history of heart disease, stroke, or cancer. That would change over the next 10 years.
During the decade-long follow up, slightly more than 4,000 of the participants -- about 2,400 of them men -- had a stroke. More than three quarters of the strokes were ischemic, in which an artery that supplies blood to the brain becomes blocked, frequently by a clot. Nearly 600 of the strokes were hemorrhagic, which occur when a blood vessel in the brain bursts.
The researchers found that consuming full-fat dairy products such as whole milk was not associated with risk of stroke. They suggest that full-fat dairy foods may increase LDL ("bad" cholesterol) levels and counteract some of the beneficial effects of eating dairy foods.
However, they did find that those who ate a daily average of four servings of low-fat cheeses, yogurts, and milk significantly lowered their risk of stroke compared to those who did not include any low-fat dairy in their diet. Even after taking into account such factors as having high blood pressure, the researchers found that the risk reduction remained significant.
Healthy Diet Is Major Part of Stroke Prevention
"This is a good study that adds to what we already know about low-fat diets," says neurologist Wayne Clark, MD, director of the Oregon Stroke Center at Oregon Health and Science University in Portland.
Clark says the calcium in dairy products may also help lower blood pressure, and he recommends two to three servings per day. However, he points out that diet is only one part of stroke prevention.
"Eating a healthy diet, quitting smoking, and increasing your exercise can reduce your stroke risk by 50%," says Clark. "Those are the big three, and by focusing on all of them, you can take control of your health."