Seasonality of mania exists in tropics
MedWire News: The effect of seasons and climate on the course of bipolar disorder extends to tropical and subtropical regions, research suggests.
Fernando Madalena Volpe and colleagues from Hospital Foundation of the State of Minas Gerais in Belo Horizonte, Brazil, found that in their region, which has tropic savannah climatic conditions, emergency psychiatric visits for mania were more frequent in late winter/spring, which correspond to the drier seasons.
“This late winter/spring peak was consistent to the findings of other southern hemisphere studies performed in temperate regions,” they note in the Journal of Affective Disorders.
The researchers analyzed a hospital registry of 5172 psychiatric visits for mania to a public psychiatric hospital in Belo Horizonte between 2000 and 2007.
The rate of emergency visits per month varied from 3.27% to 8.87%. The estimated mesor (rhythm-adjusted mean) was 5.26% and the amplitude was 0.35%.
Correlations of the rate of admissions for mania to climatic variables showed a minor, but significant, pattern of a late winter/spring peak and a nadir in February (late summer).
The regression model including secular (40.1%) and seasonal (4.3%) components explained 44.4% of the variance in the rate of visits for mania. Total visits, however, showed no seasonal distribution.
The researchers note that the estimated peak of visits for mania coincided with late winter and early spring, which are the colder, dryer, and more luminous seasons in Belo Horizonte.
Also, the rate of emergency visits for mania correlated negatively with relative humidity and rainfall.
“Altogether, climatic variables explained 8.1% of the variance in the rate of emergency visits for mania,” the team reports.
They say that the existence of seasonal variations in mood episodes opens a line of investigation regarding the mechanisms that trigger bipolar episodes at specific times of the year.
“Presently, the dominant hypotheses for seasonality of bipolar disorder involve the seasonal variation of serotonin and melatonin metabolisms, nonetheless there remain many open questions to be clarified regarding etiology and pathophysiology,” the researchers explain.
They conclude: “The influence of seasons and climate on the course of bipolar disorder is not restricted to regions of high latitudes and intense climatic variations, being extensive to tropical and subtropical regions.”
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By Lucy Piper