**5.1.4 Seasonal temperature and the development of cardiovascular diseases**

It is interesting to note that seasonal temperature itself has an impact on mortality and incidence of cardiovascular diseases. For instance, it is known for a long time that there is an inverse relationship between outside average temperature and blood pressure levels (Rose, 1961; Hata et al., 1982). In Montreal (Canada), where outside temperature varies from -24°C to 27 °C on a yearly average, a study on 2,000 patients with a total of 42,813 blood pressure readings showed a significant inverse relationship between blood pressure and average outside temperature (Kuneš et al., 1991). More recently, a 1°C reduction in daily mean temperature was associated with a 2% cumulative increase in risk of myocardial infarction over the current and following month, with the strongest effects observed after lags of 1 and 2 weeks (Bhaskaran et al., 2010). In many countries, death rates in winter are 10-25% higher as compared to the rest of the year (Curwen, 1991). When corrected for confounders, only temperature showed a constant correlation strongly suggestive of causality. Therefore, stressors that are impacting body temperature should not be seen merely as a side effect of immobilisation. We do think that these must be taken into account when measuring blood pressure and techniques for blood pressure determination that are minimizing stress and its manifestation must be favoured.
