April 19, 2012 -- Middle-aged and older adults may be able to lower their risk of having a stroke by eating low-fat dairy products, according to a Swedish study published in the journal Stroke.
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."
"One potential mechanism by which low-fat dairy foods may reduce the risk of stroke is through vitamin D," says Larsson. "Low-fat dairy foods are fortified with vitamin D in Sweden and in the U.S."
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.