Lead author Dr. Gotaro Kojima of the John A. Burns School of Medicine at the University of Hawaii in Honolulu said sunlight is generally the greatest source of vitamin D, but synthesizing it from the sun gets more difficult as one ages, so older people are advised to eat more foods rich in vitamin D -- fortified milk, breakfast cereal, fatty fish and egg yolks -- or take supplements.
Study participants included 7,385 Japanese-American men who were age 45-69 and living in Hawaii in the mid- to late-1960s when they were first examined and interviewed about what they had eaten in the previous 24 hours.
Researchers separated the participants into four groups of approximately 1,845 each -- depending on how much vitamin D they had consumed.
The researchers analyzed study participants' medical records through 1999, roughly 34 years after the initial exams, to determine the incidence of stroke. Strokes occurred in 960 men during the follow up period.
After factoring in age, calorie intake, body-mass index, hypertension, diabetes, cigarette smoking, physical activity, cholesterol levels and alcohol intake, the study found men who consumed the least dietary vitamin D had a 22 percent higher risk of stroke and a 27 percent increase risk of ischemic -- blood-clot related -- stroke compared to those consuming the highest levels of vitamin D.
The findings were published in the journal Stroke.