A population-based cohort study in Sweden found there was no association between cannabis use in young adulthood and early stroke. However, there was an association between cigarette smoking and early stroke.

Lead researcher Daniel Falkstedt, PhD, of the Karolinska Institutet in Stockholm, Sweden, and colleagues published their results online Dec. 27 in Stroke.

Previous research showed that approximately 90 percent of strokes were attributable to modifiable risk factors such as tobacco smoking, alcohol consumption, poor diet, low physical activity and hypertension, according to the researchers. Studies also had varying findings on the association between cannabis smoking and the risk of stroke.

For this study, the researchers evaluated 49,321 men in Sweden who were born between 1949 and 1951 and were conscripted into military service between 18 and 20 years old. The men had an extensive health examination and completed one questionnaire focused on social and behavioral factors and another questionnaire focused on substance use.

The researchers divided the participants into groups based on their cannabis, tobacco smoking and alcohol use. They followed the participants from 1971 until 2009 to assess the initial occurrence of fatal or nonfatal strokes.

During the follow-up period, there were 1,037 first-time strokes, of which 48 percent were ischemic strokes and 23 percent were hemorrhagic strokes. In addition, 192 first-time strokes occurred before the participants turned 45 years old, of which 40 percent were ischemic strokes and 27 percent were hemorrhagic strokes.

Men who had a stroke were more likely to have a parental history of cardiovascular disease, be overweight, have low cardiorespiratory fitness, have a low socioeconomic position in childhood, be heavy smokers and/or drink higher amounts of alcohol.

The researchers found that cannabis use showed no association with stroke before 45 years old. However, they noted that the incidence of stroke before 45 was approximately six times higher among men who smoked more than 20 cigarettes per day compared with men who did not smoke and was four times higher among men reporting high alcohol consumption compared with men reporting no alcohol use.

Multivariable models showed that cigarette smoking, but not cannabis use or alcohol consumption, was robustly associated with stroke before age 45.

There was also no significant association between cannabis use and the overall incidence of stroke until age 59. However, there was a dose-response shaped association between cigarette smoking and stroke. The researchers noted there was also the suggestion of an association between alcohol consumption and stroke.

After the researchers adjusted for cigarette smoking and alcohol consumption, none of the cannbis groups had an elevated risk of stroke. Multivariable adjusted models also found that there was no elevated risk of stroke among heavy cannabis users.

The researchers acknowledged a few limitations of the study, including that they had no follow-up data on the baseline measurements. They had no information on body mass index, blood pressure and cardiorespiratory fitness later in life, which could have contributed to or explained strokes. They also did not know whether the men continued or discontinued using cannabis, alcohol or tobacco. In addition, the study only included men in Sweden born between 1949 and 1951, so the results might not be generalizable to other patient populations.

“Previous studies on cannabis and stroke are mainly clinical, retrospective, and cross-sectional,” the researchers wrote. “We have expanded current knowledge by examining cannabis use in young adulthood in relation to the subsequent risk of stroke in a large population-based cohort. We found no evident association between cannabis use and stroke, including stroke before 45 years of age. Tobacco smoking, however, showed a clear, dose–response shaped association with stroke across multivariable models.”