Smoking increases the risk of stroke and could even cause this stroke. This is the conclusion of a Finnish study based on a cohort of twins.
- A Finnish study claims that the onset of subarachnoid hemorrhage – a form of stroke – is caused more by lifestyle than genetics.
- In their study, they claim that smoking twins are 2.5 times more likely to have a subarachnoid hemorrhage than their non-smoking co-twins.
- One of the twins who smokes would be 2.5 times more likely to have a meningeal hemorrhage than his non-smoking co-twin
Could cigarettes promote the appearance of a ruptured aneurysm? This is the intuition of researchers from the University of Helsinki (Finland) for whom “one of the largest twin studies to date has suggested that subarachnoid hemorrhage (SAH) [aussi appelée hémorragie méningée soit un AVC souvent provoqué par une rupture d’anévrisme, NDLR] is mainly of non-genetic origin, but the causal effect of environmental factors on SAH is still unknown.“So why not smoking, the toxicity of which is no longer to be demonstrated? To see whether or not smoking has an effect on the occurrence of a stroke, they looked for an answer in the huge database of a giant cohort of Finnish twins. Based on these results published on September 17 in the journal Strokethey claim that the smoking twin is three times more likely to die of a stroke than their non-smoking pair.
At the base of this intuition, a previous study called “Nordic Twin Study” where scientists had noticed that “most sets of twins were discordant for subarachnoid hemorrhage, i.e. only one of the twins died from it“without that”the role of risk factors in explaining this discrepancy has been studied“. To clarify the reason why only one of the twins would die of a stroke and not both, they queried the huge database of 32,564 Finnish twin siblings. They classified them by genetic similarity, sex , as well as their tobacco consumption – light smokers (<10 cigarettes per day), moderate smokers (10-19 cigarettes/day) and heavy smokers (>20).
Smoking increases the risk of subarachnoid hemorrhage by 2.5
Based on this data, the researchers reclassified twin pairs as ‘discordant’ if one dies of a stroke and the other does not, ‘concordant’. if both died of a stroke. “Over 869,469 person-years of follow-up, we identified 120 fatal stroke events – 71 women; median age at death 61.4 years”, write the Finnish scientists. They then compared these results with the risk factors of alcohol and smoking. For lack of a sufficiently large sample, they do not know whether heavy alcohol consumption (more than 21 g of alcohol per day) increases the risk of fatal SAH. However, they calculate that smoking causes a 2.5 times increased risk of subarachnoid hemorrhage.
Of the twin cohort of 16,282 pairs of same-sex twins, they notice that subarachnoid hemorrhage affects smokers more frequently. Out of 24 “discordant” pairs, stroke wins out the smoking twin in 20 pairs. In the remaining 4 pairs, it is the non-smoker who dies of subarachnoid hemorrhage. Scientists note that “smoking increased the fatal risk of subarachnoid hemorrhage regardless of gender or zygosity of twin pairs.“For them, tobacco can cause subarachnoid hemorrhage.
Scientists point out that the occurrence of subarachnoid hemorrhage is caused more by behavior than by genetic heritage. If smoking seems to cause it, it is not the only factor. High blood pressure and female sex are associated with a slightly increased risk of stroke, but according to the researchers”none of these associations was as clear as the relationship between smoking and subarachnoid hemorrhage.“However, the size of the sample could perhaps attenuate this result, as could the failure to take into account non-fatal subarachnoid hemorrhages or the excessively small proportion of former smokers. Limits which, according to the authors of the study, cannot do not call into question the responsibility of tobacco in the onset of fatal subarachnoid hemorrhage.
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