Abstract and Introduction
The influence of temperature changes on risk factors like hypertension is often disregarded despite extensive literature on the phenomenon. Numerous surveys and studies have documented the correlation between temperature and blood pressure in various countries among adults, the elderly, and children. Twenty-four-hour blood pressure studies also generally show higher blood pressure in the winter. The suggested etiology is that cold increases sympathetic tone, evidenced by elevated blood pressure and plasma and urinary noradrenaline concentrations. The lower blood pressure in warm temperatures is attributed to cutaneous vasodilatation and loss of water and salt from sweating. Taking seasonal variations in blood pressure into account will increase the meaningful information collected in population surveys and mass screenings. It will also result in more personalized management of antihypertensive medications tailored to the individual.
Both doctors and patients are aware of the effects of changes in temperature on blood pressure. Patients in the borderline-to-mild hypertensive range often need pharmacologic treatment only in winter, and hypertensive patients themselves may spontaneously decrease their medications during summer. Despite the published evidence of the clinical influence of temperature changes on risk factors like hypertension, this phenomenon is often overlooked. As early as 1921, blood pressure was found to be higher in cold than in warm months by Hopman and Remen,[1] and systolic blood pressure was 20-30 mm Hg higher on cool days than at other times according to Kauffmann in 1924.[2] Moreover, the prevalence of strokes and myocardial infarction was found to increase in winter.[3,4]
Brown, as early as 1930,[5] described the daily and monthly rhythms in blood pressure of men with essential hypertension. He noted a lowering of the blood pressure during the summer months of each year and the important implications of the probable effect of season on the vasomotor mechanism for the management of hypertension.[5] The lowering of blood pressure in summer was documented by Rose[6] and subsequently confirmed by several other groups.[7,8,9,10,11,12] The British Regional Heart Study found both environmental temperature and humidity to be significantly associated with blood pressure, although considered to be of minor importance.[13]
The correlation between air temperature and blood pressure was also found in various surveys of children: in the Minneapolis Children's Blood Pressure Study,[14] in Great Britain,[15] and in a study in Australia[16] where a change of 10°C in temperature was estimated to cause a 5-7 mm Hg difference in blood pressure.
The seasonal variation in blood pressure is often recognized in epidemiologic studies, but few have developed quantitative formulations to correct the seasonal bias in data. After all, temperature varies considerably between summer and winter in tropical and subtropical countries, and in Nordic countries, particularly Finland, they may range from -30°C in winter to +30°C in summer.[17] This seasonal variation in blood pressure was documented in a number of countries: in Iraq[10] with its hot, dry summers and cold, humid winters where differences were small and only systolic pressure in normotensive subjects was statistically significant; in Montreal[18] where systolic blood pressure varied as much as 7 mm Hg and diastolic blood pressure varied 3 mm Hg within the 24°C to 27°C temperature range; and in northern Japan where an obvious elevation in blood pressure in winter was reported by Sasaki et al.,[19] who recorded blood pressure in 831 inhabitants of Hirosaki in winter and summer over a 5-year period.
In north India,[20] the proportion of patients with hypertension (with and without coronary artery disease) was the greatest in winter and declined during summer. In Shandigar, northwest India,[21] where the temperature varies from a maximum of 46°C during May and June to a minimum of 1-2°C in winter, average systolic and diastolic blood pressures were higher in winter in 15 hypertensive patients as well as in controls.
A drop in systolic and diastolic blood pressures was recorded in 1142 hypertensive psoriatic patients during 4 weeks.[22] Although there was no significant difference between age groups in lowering diastolic blood pressure, there was marked decrease in systolic measurements between the younger and older subjects. A decline in blood pressure was attributed to temperature as well as to the bromide-rich atmosphere hanging over the Dead Seaa chemical with known sedative and mild hypnotic effects.[23]
It is also of interest that blood pressure was found to vary seasonally in patients with end-stage renal disease undergoing hemodialysis, with higher values recorded in winter and lower values in summer.[24] Despite the recognized extracellular volume overload, the pattern of blood pressure changes was clearly seasonal.
Am J Geriatr Cardiol. 2004;13(5) © 2004 Le Jacq Communications, Inc.
Cite this: Seasonal Variations in Blood Pressure - Medscape - Sep 01, 2004.
