Seasonal Variations in Blood Pressure

Talma Rosenthal, MD

Disclosures

Am J Geriatr Cardiol. 2004;13(5) 

In This Article

Etiology

Numerous physiologic parameters have been related to the effects of heat and cold. Prominent among them is the increased sympathetic system activity manifest by increased urinary and plasma catecholamines[8] that were implicated in the rise in blood pressure during the winter season. There was a linear correlation between urinary corticosteroid levels and the mean temperature on the days of urine collection, with values being approximately 40%-50% lower in summer (36°C mean temperature) than in winter (13°C mean temperature). The findings of Hata et al.[8] were previously reported by Ahuja and Sharma[64] who found higher mean levels of 24-hour urinary 17-hydroxy corticosterone, 17-oxysteroids, and 17-oxogenic steroids in December, January, and February when the environmental temperature was low. Levels fell gradually from February, reached the lowest levels in May, June, and July when the temperature was high, and gradually rose again as the next winter drew near.

Profuse sweating at higher temperatures was implicated as well, as it leads to hypovolemia and elevated plasma osmolality that cause increased secretion of mineralocorticoids and antidiuretic hormone,[65] which, by their action on the renal tubules,[64]conserve sodium and water. Increased sodium loss in sweat in summer was also cited by Hata et al.[8]as a possible reason for the higher urinary sodium excretion in winter observed in patients with essential hypertension. These authors felt that the 20-34 mEq differences in urinary sodium excretion recorded between the seasons might be due to salt loss in sweat in the summer. These findings are supported by several other investigators,[66,67,68,69] who found that exposure to heat tends to decrease blood pressure because of cutaneous vasodilatation and water and salt loss through sweating.

Other factors implicated in the physiologic reaction to temperature include increased salt load presented to the kidneys[8] and prolonged or repeated exposure to heat that can reduce the salt content of sweat considerably (up to 95%) and decrease renal excretion of sodium and chloride. This latter process occurs apparently as a result of increased aldosterone secretion and ultimately produces a positive sodium balance and increased plasma volume.[70]

With regard to the decrease in blood pressure in summer, Sharma et al.[11] and others, including the Medical Research Council Treatment Trial for Mild Hypertension, suggested[7,8] that the decrease was a result of vasomotor effect of warm temperature.

The data and observations described here underscore the need to establish different normal ranges according to the season of the year when estimating the frequency of hypertension in a community, at least in certain parts of the world. Population surveys in general should routinely factor in the seasonal variation in blood pressure. Awareness of this phenomenon will result in more personalized, tailored dosages of antihypertensive medications.

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