Downloaded from heart.bmj.com on August 19, 2014 - Published by group.bmj.com Heart Online First, published on July 23, 2014 as 10.1136/heartjnl-2014-306160 Editorial The hazard of rounding Cape Horn: is it changing? Pietro Amedeo Modesti1,2 …he who goes the oftenest round Cape Horn goes the most circumspectly. Herman Melville, “White-Jacket”, 1850 Notwithstanding the range of strategies to help one cope with the cold weather, most countries experience mortalities in excess of 5–30% in winter, brought on mainly by cerebrovascular events.1 This variability is mainly attributed to the population being able to keep themselves warm, both indoors and outdoors, necessitated by the mean cold temperature. Policies and measures to increase efficient use of energy indoors, coupled with advice to citizens suggesting to wear adequate warm protective clothing and to keep themselves active when out in the open, have been thus promoted. The elderly are aware of the risks, and traditionally perceive winter as a rounding of Cape Horn. Consequently, the result of exposure to acute cold may trigger vasoconstriction, with a rise in blood pressure (BP), and myocardial ischaemia in patients with coronary artery disease. This acute response is considered in all guidelines on BP measurement which recommend the importance of standardised room temperature when assessing BP values. However, a negative relationship between outdoor temperature and BP values was consistently observed even when measurements were taken in comfortably warm rooms.2 In the French Three-City study3 that prospectively investigated 8801 participants over the age of 65 years, average systolic BP was 5 mm Hg higher in winter than in summer. This variation was independent of anthropometric data and baseline BP values, but rather related to the subjects’ age. Variations in BP were greater in subjects 80 years of age or older, than in younger participants. In the reanalysis of data collected in the World Health Organization Monica Project (monitoring trends and determinants in cardiovascular 1 Department of Clinical and Experimental Medicine, University of Florence, Florence, Italy; 2Centre for Civil Protection and Risk Studies, University of Florence (CESPRO), Florence, Italy Correspondence to Professor Pietro Amedeo Modesti, Department of Clinical and Experimental Medicine, University of Florence, Largo Brambilla 3, Florence 50134, Italy; pamodesti@unifi.it disease) risk factors surveys,4 including 25 populations in 16 countries (115 434 participants aged 35–64 years) the effect of outdoor temperature remained after controlling for indoor temperature, as a 1°C increase in outdoor temperature reducing BP values by 0.14 mm Hg (95% Cl −0.23 to −0.05, adjusted for indoor temperature). Conversely, the effects of the winter season disappeared after controlling for outdoor temperature, suggesting that a major component of the seasonal change in BP was the direct result of temperature.4 As physicians, we often have to deal with the effects of temperature in treating hypertensive patients even during summer, when we encounter the potential implications of falls or acute renal failure caused by a marked reduction in BP especially in the elderly. As a consequence, (although not considered in hypertension guidelines) physicians often resort to seasonal adaptation of antihypertensive drugs in their clinical practice. The influence of temperature, or at least seasonality, is conversely less considered in epidemiological studies investigating the burden of risk factors in populations. The importance of conducting an epidemiological study throughout a whole year, or at least to declare the exact timing of the study in the final report, is indeed not always given due importance. A recent large epidemiological survey aimed at assessing hypertension burden at the population level, BP is the main factor guiding cardiovascular (CV) risk stratification, including the measurement of temperature as one of the parameters investigated.5 In the Hypertension and Diabetes in Yemen (HYDY) study, an increase of 1°C in air temperature reduced hypertension with an OR of 0.98 (95% confidence limits: 0.96–0.99) at logistic regression analyses adjusted for age, gender, education and average air temperature at the two survey visits.5 The elegant study by Marti-Soler et al6 shows that, beside systolic BP levels, which were, on average, 3.5 mm Hg lower in summer than in winter, other CV risk factor levels tended to be higher in winter and lower in summer. In particular, in the Northern Hemisphere, the estimated seasonal variations were 0.26 kg/m2 for Body Mass Index, 0.6 cm for waist circumference, 0.02 mmol/L for triglycerides, 0.10 mmol/L for total cholesterol, 0.01 mmol/L for highdensity lipoprotein cholesterol, 0.11 mmol/L for low-density lipoprotein cholesterol, and 0.07 mmol/L for glycaemia. Similar seasonal variations were found in the Southern Hemisphere, with the exception of waist circumference, HDL and LDL cholesterol.6 Therefore, the resultant estimate of individual CV risk varied depending on the season. As a consequence, at the patient level, only a low value in winter can thus be considered a low ‘yearly’ value, whereas a low value in summer does not mean a low value in winter. At the population level, seasonal differences may be important because CV risk estimation plays a key role in the efficient allocation of resources.5 This aspect is especially important for low-income countries, but any speculation is limited by the small number of studies carried out in the Southern Hemisphere, and by the absence of studies investigating populations from Asia, Africa and South America.6 As variations in weather patterns and adaptive abilities are determined by latitude, a differential effect of temperature on mortality has been found. The temperature of the lowest temperature-associated mortality observed in a city (minimum mortality temperature), was shown to vary by latitude. People who live in cities located at higher latitudes, have lower minimum mortality temperatures, while people who live in cities located at lower latitudes have higher thresholds in coping with ambient temperatures. The large majority of studies included in the analysis6 were conducted in European countries. In this setting, the possibility of comparing between-countries differences in the seasonal variations of BP and CV risk, might give an insight into the range of distribution of excess winter mortality across Europe. More precisely, excess winter mortality was found to be higher in Southern Europe (Portugal and Spain), than in Scandinavia and Northern Europe (Finland and Germany).7 In Europe, thermal efficiency of housing, as well as the capability to cope with cold weather, were indeed found to increase with rising latitude.8 In the reanalysis of BP data collected within the WHO MONICA Project,4 the random effects that seasons had on the main risk factor for CV events (BP), were latitude-dependent being lower for countries with colder climates, and higher for countries with warmer climates. Conversely, no association between the estimated amplitude of seasonal BP variations and latitude was observed by Marti-Soler et al6 (figure 1). The numbers Modesti PA. Article Heart Monthauthor 2014 Vol (or 0 No their 0 1 Copyright employer) 2014. Produced by BMJ Publishing Group Ltd (& BCS) under licence. Downloaded from heart.bmj.com on August 19, 2014 - Published by group.bmj.com Editorial Figure 1 (A) Population-specific seasonal change in systolic blood pressure against latitude. Reproduced from Barnett et al4 with permission of the publisher. (B) Estimated amplitude of seasonal changes in blood pressure by latitude. Reproduced from Marti-Soler et al6 with permission of the publisher. of populations and countries included in the two studies, are comparable; the model adopted to estimate seasonal BP variations is also similar. Nevertheless, the different representations of extreme latitudes might play a role. The large majority of studies included by Marti-Soler et al6 were, however, performed after 1997 (only 8 out of the 23 studies were started before 1997), whereas the collection period of studies included by Barnett et al4 ranged from 1979 to 1997. In England and Wales, the association of year-to-year variation in excess winter mortality with the number of cold days in winter (<5°C), evident until mid-1970, has recently disappeared 9 and the link between winter temperature and excess winter mortality is no longer as strong as before. Historical trends in excess winter mortality also show a gradual reduction in deaths between 1980 and 2011. Those changes could probably be linked to the improved energy efficiency in homes and the quality of housing.9 The relationship between weather and winter mortality is probably altered 9 and the discrepancies between the two studies might 2 disclose a reduced latitude-dependency of the influence of winter on BP. Is it the end of a myth? Probably not. The variability observed by Marti-Soler et al6 in the distribution of seasonal variation of BP by latitude might also indicate that policy changes are non-homogeneously occurring in Europe. Cape Horn is still Cape Horn, never a place to be treated lightly. 2 3 4 5 Competing interests None. Provenance and peer review Commissioned; internally peer reviewed. To cite Modesti PA. Heart Published Online First: [please include Day Month Year] doi:10.1136/heartjnl2014-306160 6 7 ▸ http://dx.doi.org/10.1136/heartjnl-2014-305623 8 Heart 2014;0:1–2. doi:10.1136/heartjnl-2014-306160 REFERENCES 1 Analitis A, Katsouyanni K, Biggeri A, et al. Effects of cold weather on mortality: results from 15 European cities within the PHEWE project. Am J Epidemiol 2008;168:1397–408. 9 Modesti PA. Season, temperature and blood pressure: a complex interaction. Eur J Intern Med 2013;24:604–7. Alperovitch A, Lacombe J-M, Hanon O, et al. Relationship between blood pressure and outdoor temperature in a large sample of elderly individuals: the Three-City study. Arch Intern Med 2009;169:75–80. Barnett AG, Sans S, Salomaa V, et al. The effect of temperature on systolic blood pressure. Blood Press Monit 2007;12:195–203. Modesti PA, Rapi S, Bamoshmoosh M, et al. Impact of one or two visits strategy on hypertension burden estimation in HYDY, a population-based cross-sectional study: implications for healthcare resource allocation decision making. BMJ Open 2012;2. pii: e001062. Marti-Soler H, Gubelmann C, Aeschbacher S, et al. Seasonality of cardiovascular risk factors—an analysis including over 230 000 participants in 15 countries. Heart Published Online First: 30 May 2014 doi:10.1136/heartjnl-2014-305623 Healy JD. Excess winter mortality in Europe: a cross country analysis identifying key risk factors. J Epidemiol Community Health 2003;57:784–9. Cold exposure and winter mortality from ischaemic heart disease, cerebrovascular disease, respiratory disease, and all causes in warm and cold regions of Europe. The Eurowinter Group. Lancet 1997;349:1341–6. Staddon PL, Montgomery HE, Depledge MH. Climate warming will not decrease winter mortality. Nature Climate Change 2014;4:190–94. Modesti PA. Heart Month 2014 Vol 0 No 0 Downloaded from heart.bmj.com on August 19, 2014 - Published by group.bmj.com The hazard of rounding Cape Horn: is it changing? Pietro Amedeo Modesti Heart published online July 23, 2014 doi: 10.1136/heartjnl-2014-306160 Updated information and services can be found at: http://heart.bmj.com/content/early/2014/07/23/heartjnl-2014-306160.full.html These include: References This article cites 8 articles, 2 of which can be accessed free at: http://heart.bmj.com/content/early/2014/07/23/heartjnl-2014-306160.full.html#ref-list-1 P<P Email alerting service Topic Collections Published online July 23, 2014 in advance of the print journal. Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article. Articles on similar topics can be found in the following collections Hypertension (2668 articles) Drugs: cardiovascular system (7874 articles) Epidemiology (3230 articles) Notes Advance online articles have been peer reviewed, accepted for publication, edited and typeset, but have not not yet appeared in the paper journal. 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