MedWire News: Uncontrolled cardiovascular risk factors are associated with an increased risk for intracerebral hemorrhage (ICH) during cold periods of the year, an analysis of registry data suggests.
The finding supports an interaction between seasonality and the acute onset of ICH in people at increased cardiovascular risk, an observation that may be useful when designing stroke prevention strategies.
The findings are reported in a letter by T Turin (Shiga University of Medical Science, Otsu City, Japan) and colleagues and published in the journal Acta Neurologica Scandinavica.
For their study, Turin and team analyzed data from the Takashima Stroke Registry, which contains information on all people with stroke in Takashima County, a region of Japan with a population of around 55,000. In all, 380 people suffered a first-ever ICH between 1988 and 2002.
Each of these individuals was classified according to the season at the time of stroke (dichotomized into warm [May–October] and cold [November–April] periods), presence of cardiovascular risk factors (namely, hypertension, diabetes, current smoking, and drinking status), and whether the risk factors were being treated at the time of stroke.
Interestingly, a higher proportion of severe strokes occurred during the colder period; 28-day case-fatality was 25.3% for strokes in the cold period versus 19.9% in the warm period.
In multivariate analysis, adjusting for conventional and lifestyle-associated risk factors, untreated hypertension was significantly associated with ICH during cold periods, with an odds ratio of 2.23.
For untreated diabetes the odds ratio was 2.59, but this did not reach statistical significance. This may reflect the small number of people with diabetes, the authors suggest.
They say that the mechanisms underlying the seasonal variation in stroke are not fully understood but are likely to be multifactorial.
“It is well known that the risk of ICH is higher in subjects with untreated hypertension and that cold exposure increases blood pressure by activating the sympathetic nervous system,” Turin et al write.
“As there is also evidence that seasonal variations in blood pressure are greater in subjects with untreated hypertension, it follows that the effect of ambient temperature on the risk of ICH may be mediated by fluctuations in blood pressure.”
The researchers conclude that their results, while not establishing causality, support the possibility that external factors may influence the acute onset of ICH in people with untreated or uncontrolled risk factors.
“The identity of these factors, which may be of significant use in stroke prevention strategies, requires further investigation,” they add.
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