Strong causal relationship between smoking and intracerebral hemorrhage

A new Finnish study shows that smokers are at increased risk of developing intracerebral hemorrhage called subarachnoid hemorrhage (SAH). SAH is a type of stroke that can be life-threatening. A study entitled “Case-control study of Finnish twins, where smoking causes subarachnoid hemorrhage, if not fatal,” was published in the journal. stroke, Journal of the American Stroke Association.

Computed tomography (CT) of the brain: Left SAH (subarachnoid hemorrhage). Image Copyright: MossStudio / Shutterstock

What has been done before?

Ten years ago, in a Nordic twin cohort study of 79,664 twins in Denmark, Finland, and Sweden, researchers examined risk factors for SAH other than genes. Because the twins share a genetic makeup, this study can analyze other environmental factors that may affect the risk of SAH. This study showed that non-genetic factors predominantly determine SAH. However, this study did not reveal the extent to which environmental factors could affect an individual’s risk of SAH.

What was this study about?

The Nordic Twin Cohort Study showed non-genetic effects on SAH risk, so this was an attempt to examine the risk factors for smoking and their effects on SAH risk. The authors wrote, “If so, such findings would suggest that smoking causes SAH.” This was a study of 32,564 brothers and sisters who found out why only one of the brothers experienced deadly SAH. They hypothesized that smoking was one of the key risk factors for SAH.

what did you do?

For this study, the team included 16,282 pairs of same-sex Finnish twins. There were a total of 32,564 individuals. They belonged to the older Finnish twin cohort from 1976 to 2018 and were closely tracked. The team searched the records to see all participants who died in SAH. From all data on participants’ health and habits, the team focused on smoking habits, alcohol usage (daily consumption per 10 g of alcohol), and regular physical activity, presence of hypertension, body mass index, and levels. The grade of education (years of education) for which information was collected. Smoker status was defined as “never, sometimes, before, and now.” Smoking status was ultimately categorized into smokers (occasional and present) and nonsmokers (previous and former). Current smokers are further categorized by the number of cigarettes per day.

Twins were classified as monozygotic (identical) or dizygotic (non-identical) twins, or unknown mating twins. They checked all siblings who died in SAH, along with other twins who did not die. They assessed individual hazard ratios across the participant group and paired when one of the pair died of SAH. When one of his brothers died, it was called a disagreement pair. The matching twin pair was a pair in which both twin brothers died due to SAH.

What did you find?

The study included a total of 869,469 follow-ups. This identified a total of 116 unmatched twin pairs and two matching twin pairs. A total of 25 pairs of unmatched twins were identical or identical twins.

The results revealed that smoking (occasional / current) status was associated with an increased risk of SAH and death from SAH compared to nonsmokers (never / previously). Hazard ratio was 3.33 [CI, 2.24–4.95].. The team said, “Both are heavy (HR, 3.01) [CI, 1.58–5.73]) And moderate smokers (HR, 3.98 [CI, 2.44–6.49]) Was at slightly higher risk than light smokers (HR, 2.83) [CI, 1.64–4.9]) ”

Among the discordant twins, smoking twins had a higher risk of death from SAH than non-smoking twins. Hazard ratio was 6.33 [CI, 1.87–21.4].. “The association was consistent, regardless of the zygosity or gender of the twin pairs,” the team wrote.

There was also an increased risk of death from SAH among those who consumed more than 21 g of alcohol per day (HR, 3.17). [0.43–23.3]).

Conclusions and implications

The team states that the study provides strong evidence that there may be a “causal link” between smoking and death from SAH.

Corresponding authors of the study, Ilari Rautalin, Ph.D. “Our study provides further evidence of the link between smoking and intracerebral hemorrhage,” a student at the University of Helsinki in Finland said in a statement.

Rosemary Robertson, Deputy Science and Medical Officer of the American Heart Association and co-head of the AHA Regulatory Science Center, said in her statement: .. Smoking cessation or quitting smoking, if already started, is an integral part of primary prevention. She was not involved in this study.