Previously it was thought that in Finland approximately a thousand people suffer subarachnoid haemorrhage (SAH) every year – most of them adults of working age. Up to half of those afflicted die within a year. Subarachnoid haemorrhage is typically caused by a ruptured cerebral aneurysm, which leads to a sudden increase in the intracranial pressure. Smoking is a key risk factor for SAH.
A Finnish study published in the journal Neurology looked at changes in the incidence of subarachnoid haemorrhage over a period of 15 years (1998-2012), and these were contrasted with changes in the prevalence of smoking. The results indicated that the number of people afflicted with SAH was nearly half of the previously assumed figure and that the number was in rapid decline, a trend which was particularly apparent in younger generations.
Within fifteen years, the prevalence of SAH had decreased by 45% among women, and 38% among men, under 50. During the same period, the prevalence of SAH decreased by 16% among women, and 26% among men, over 50. Smoking among Finns aged 15-64 decreased by 30% during the monitoring period.
“It is extraordinary for the incidence of any cardiovascular disease to decrease so rapidly at the population level in such a short time,” says Professor Jaakko Kaprio from the University of Helsinki, one of the primary authors of the study and director of the Institute for Molecular Medicine Finland. “Even though we cannot demonstrate a direct causation in nation-wide studies, it is highly likely that the national tobacco policies in Finland have contributed to the decline in the incidence of this type of severe brain haemorrhage.”
Cerebral aneurysms are fairly common – they are present in up to more than 10% of people over the age of 70 – but most of them never rupture. For decades, researchers have been searching for factors which could be used to identify persons at high risk of aneurysm ruptures and who should consequently be treated.
“Previous studies have indicated that smoking is one of the most important susceptibility factors for rupturing aneurysms, so in that sense the now established connection between a decrease in smoking and a decrease in SAH is not surprising,” says the other primary author of the new study, Miikka Korja, a neurosurgeon at Helsinki University Hospital.
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Associate Professor Miikka Korja, MD, PhD University of Helsinki and Helsinki University Hospital
Reference: Korja M, Lehto H, Juvela S, Kaprio J. Incidence of subarachnoid hemorrhage is decreasing together with decreasing smoking rates. Neurology, 2016. Published online ahead of print 12 Aug, 2016 DOI: 10.1212/WNL.0000000000003091