Smoking most likely has a significant share in all cases of subarachnoid haemorrhage, the most fatal type of cerebrovascular disturbances in the brain, warn researchers.
The study, published in the journal Stroke, reaffirmed a link between smoking and subarachnoid haemorrhage (SAH), a type of bleeding stroke that occurs under the membrane that covers the brain and is frequently fatal.
"Our study provides evidence about the link between smoking and bleeding in the brain," said study researcher Ilari Rautalin from the University of Helsinki in Finland.
This study utilised health care data from the Finnish Twin Cohort, a national database of 32,564 individuals (16,282 same-sex, twin pairs in Finland) who were born before 1958 and alive in 1974, and followed for over 42 years between 1976 and 2018.
The researchers sought to clarify the factors involved when only one twin suffered from fatal bleeding in the brain and hypothesised that smoking - the most important environmental risk factor - could play a significant role.
Researchers identified 120 fatal bleeding stroke events among the twins, and the strongest link for a fatal brain bleed was found among smokers.
Data collected from surveys included smoking; high blood pressure (diagnosis or use of antihypertensive medications), physical activity, body mass index, education, and alcohol use.
Participants were separated into two groups: smokers (occasional or current) or non-smokers (never and former). Current smokers were classified according to the number of cigarettes smoked per day: light, less than 10; moderate, 10-19; heavy, 20 or more.
The analysis of the 120 fatal bleeding events found four fatalities occurred among both twins in two pairs.
In the remaining 116 fatalities, one twin died of bleeding in the brain, while the other died of another cause, migrated during the follow-up or was still alive at the end of the study follow-up.
Heavy and moderate smokers had three times the risk of fatal bleeding in the brain, while light smokers had slightly less at 2.8 times the risk.
According to the study, the median age at the fatal brain bleed was 61.4 years.
Risk factors such as high blood pressure, lower physical activity rates and being female were not found to be significant influences in this investigation, unlike prior studies.
"Smoking was associated with fatal bleeding in the brain consistently in both men and women and with bleeding stroke deaths within twin pairs where only one of the twins died from a SAH," the study authors wrote.