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Seasonal variation in 24 h blood pressure profile in healthy adults- A prospective observational study


The clinical and experimental data on seasonal variation in blood pressure is mainly from office and home blood pressure (BP) monitoring studies. There are few studies from temperate climates on seasonal changes with ambulatory blood pressure (ABP) monitoring and none from India. This is a prospective, observational study among healthy adults. ABP was measured in four different seasons in 28 subjects. Mean arterial pressure (MAP), ambulatory systolic blood pressure (SBP), and ambulatory diastolic blood pressure (DBP) were significantly higher in winter compared to summer season. 24-hour MAP was lowest in summer while highest MAP was recorded in winter (97.04 ± 8.30 and 103.89 ± 8.54, respectively). The mean difference was −6.86 mm Hg (95% CI: −10.74 to −2.97, p = 0.001). This difference was mainly due to increase in day time MAP. There was no difference in 24 h systolic and diastolic blood pressure between summer and winter. There was significant difference between summer and winter in the SBP (day time) [125.61 ± 11.44 and 131.93 ± 9.46, mean difference −6.32 (95% CI: −10.69 to −1.95, p = 0.005)] and DBP (day time) [79.57 ± 9.95 and 87.07 ± 9.9, mean difference −7.50 (95% CI: −12.49 to −2.51, p = 0.003)]. The night time systolic and diastolic BP was similar during winter and summer. Thus, BP increases significantly during winter compared to summer season. This change is primarily in the day time systolic, diastolic and mean blood pressures. Larger studies are required to further validate our findings.


Seasonal fluctuation in blood pressure (BP) is a well known phenomenon [1,2,3,4]. BP increases during winter season and decreases during summer season [4]. Change in outdoor temperature with change in season is a major determinant of the observed seasonal fluctuations. An inverse association between ambient temperature and BP has been observed in several studies [4,5,6,7,8,9,10,11]. Most of these studies were conducted in developed countries and temperate regions of the world [12,13,14,15,16]. There is limited data from India and other tropical countries [1, 3]. Tropical countries have different climatic conditions with extreme temperature variations [1]. Summers are extremely hot and temperature touches near zero during winters. Also, housing conditions (access to central heating) and other known risk factors of hypertension (age, dietary habits, obesity and social stress) are quite different as compared to developed countries that can modify the effect of season on blood pressure.

Seasonal variation of blood pressure has been shown in office BP, home BP and ambulatory BP studies [12]. ABP monitoring is far superior to office based BP monitoring in predicting cardiovascular events and for risk stratification [13]. ABP is also a better representative of actual BP since office BP is affected by both observer related errors and patient related factors. ABP is also useful in studying abnormalities of the diurnal rhythm, dippers/non dippers, the short-term variability, masked hypertension, white coat hypertension and pseudo resistant hypertension. It is therefore important to study the effect of change in weather on ABP.

To the best of our knowledge no observational study is available from India on the effect of weather on ABP either in healthy subjects or patients. Aim of our study was to evaluate seasonal variation in 24 h blood pressure profile in healthy adults across four seasons.


This is a prospective observational study conducted in 50 asymptomatic health care personnel working in Ludhiana, Punjab, India. The latitude and longitude of Ludhiana city are 30.9010° N, 75.8573° E. The subjects were followed for four seasons of the year as follows: spring (1st March to 30th April), summer (1st June to 31st July), post monsoon (1st September to 31st October) and winter (1st December to 31st January).

Fifty subjects were enrolled in summer season out of which 28 participants completed four seasons follow up (Fig. 1). So the analysis was limited to 28 subjects. Among the study participants 4 were working as nursing staff, 5 were security personnel, 15 were engaged in clerical work, 2 were mechanics, 1 was doctor and 1 was tailor. ABP was measured using BR-102 plus 24/48 h blood pressure machine by Schiller. Left arm was used for measuring BP as recommended in guidelines. BR-102 is a menu guided machine, user programmable unit enabling long term BP measurement to be taken at preset intervals. It can take up to 100 measurements over a 24 h period with all recorded data stored in the internal memory.

Fig. 1

Flowchart of data collection

The ABP measurements were done at the following intervals: 5 am to 5 pm every 15 min, 5 pm to 10 pm every 30 min and 10 pm to 5 am every 60 min. Day time was taken as time period from 6 am onwards till 10 pm and night time was taken from 10 pm onwards till 6 am. Different cuff size were used according to the mid arm circumference.

The following measurements were looked at: 24 h mean, systolic and diastolic BP, day time mean, systolic and diastolic BP, night time mean, systolic and diastolic BP, early morning surge (EM Surge) and early morning first hour SBP and DBP (EM 1st hr). Early morning surge was defined as BP during first 4 h of awakening.

Information on demographic characteristics of subjects such as age, gender etc. were recorded on a pre designed proforma. Physical activity, smoking and alcohol consumption were noted. Weight and height were measured during each season. BMI was calculated using standard formula: weight(kg)/height(m)2.

Hypertension was defined according to European Society of Hypertension position paper on ambulatory blood pressure monitoring. Non dippers were defined as patients with nocturnal fall in BP by <10% and those with rise in nocturnal BP were labelled as reverse dippers [17].

All the subjects were informed regarding the procedures and objectives of the study. A written informed consent was obtained. The study was approved by institutional ethics committee.

Metrological data

The data about temperature were provided by local agency of national weather service, Punjab Agricultural University, Ludhiana during four different seasons of the year. The maximum temperature during spring, summer, post monsoon and winter seasons was 30.77 ± 4.38, 37.60 ± 3.44, 32.41 ± 2.20 and 19.52 ± 3.60 °C, respectively. The minimum temperature was 15.0 ± 4.48, 27.71 ± 2.51, 21.73 ± 3.80 and 6.67 ± 2.71 °C, respectively. There was significant difference in maximum and minimum temperature between summer and winter season (p < 0.001).

Statistical analysis

Data has been expressed as mean ± SD for quantitative variables and as frequency (%) for qualitative variables. Statistical significance of categorical variables was determined by Chi-square test and Fisher’s Exact test. For quantitative variables, Generalised estimating equation (GEE) method with first order auto regressive covariance structure was applied for comparison among 4 seasons. p < 0.05 was taken as a level of statistical significance. Pairwise multiple comparisons among the 4 seasons were done by Wald Chi-square test. Bonferroni correction was applied. p < 0.01 was considered as significant for pairwise comparisons.


The ABP readings were analysed in the 28 subjects who completed four seasons follow up (Fig. 1). Demographic characteristics of 28 subjects are given in Table 1. The mean age was 39.54 ± 5.91 years. 22(78.57%) were males and 6(21.43%) were females.

Table 1 Demographic characteristics of study participants (N = 28)

5 (17.9%) subjects gave history of alcohol intake and 1 (3.6%) gave history of smoking. Most of them were having a sedentary life style (96.4%) with only 1(3.6%) involved in regular physical activity. Twenty among them were vegetarian and eight were non vegetarian. Thirteen (46.4%) subjects had normal BMI, eleven (39.3%) were overweight and four (14.3%) were obese. Twenty four (85.7%) subjects worked in air conditioned environment.

Line diagrams depicting seasonal trends in various above mentioned ambulatory blood pressure parameters are shown in Figs. 2, 3 and 4. Overall there was a trend towards lower BP during summer among various components of ABP except night time BP, which was lowest in post monsoon season. Seasonal comparison of various components of MAP, SBP and DBP is given in Tables 2 & 3. There was significant difference in MAP (24 h) and MAP (DT) among four seasons. Minimum MAP (24 h) and MAP (DT) were recorded in summer season while maximum values were recorded during winter season [MAP (24 h) = 97.04 ± 8.30 in summer vs 103.89 ± 8.54 in winters; MAP (DT) = 99.57 ± 9.76 in summer versus 107.64 ± 8.97 in winters]. On pairwise comparisons with Bonferroni adjustment, significant difference in MAP (24 h) and MAP (DT) was only seen between summer and winter season (Table 3). The mean difference for MAP (DT) and MAP (24 h) was −8.07 (95% CI:−12.38 to −3.76, p < 0.001) and −6.86 (95% CI: −10.74 to −2.97, p = 0.001), respectively.

Fig. 2

Line diagram depicting trends in MAP across four seasons

Fig. 3

Line diagram depicting trends in ambulatory systolic blood pressure (mm Hg) across four seasons

Fig. 4

Line diagram depicting trends in ambulatory diastolic blood pressure (mm Hg) across four seasons

Table 2 Comparison of ambulatory blood pressure (mm Hg) across four seasons
Table 3 Intergroup comparison of ambulatory blood pressure (mm Hg) across four seasons

SBP (DT) showed significant difference among four seasons (p = 0.045) by GEE method. After pair wise comparisons with Bonferroni adjustment, the difference between summer and winter was statistically significant [−6.32 (95% CI:−10.69 to −1.95, p = 0.005)]. No other pair wise comparisons were found to be significant for SBP (DT). There was no difference in other SBP (Mean, EM 1st hr and EM Surge SBP) parameters among different seasons.

DBP was highest in winters, intermediate in post monsoon and lowest in summer season. There was significant difference in DBP (mean), DBP (DT) and EM surge of DBP across four seasons (p < 0.05) with GEE method. After pair wise comparisons, DBP (DT) and EM Surge DBP showed significant difference between summer and winter seasons [−7.5 (95% CI: −12.49 to −2.51, p = 0.003) and −10.32(95% CI: −17.7 to −2.92); p = 0.006]. For DBP (mean), summer winter difference was −5.64 (95% CI: −10.05 to −1.23) which was just short of being statistically significant (p = 0.012). Post monsoon DBP (mean) and DBP (DT) were significantly higher than summer season (p < 0.01) while EM Surge DBP difference was not significant (p > 0.01). EM Surge DBP was higher in spring compared to summer [8.11 (95% CI: 2.69 to 13.52, p = 0.003)]. There was no difference in EM 1st hr DBP across four seasons.

Table 3 shows that the night time blood pressures did not show a significant difference between summer and winter. There was no significant difference across four seasons in the MAP and DBP. The SBP showed difference in the NT pressures across four seasons. Non dippers and reverse dippers were higher in summer as compared to winter season but this difference was statistically non significant (Table 4). Heart rate showed no significant variations among four seasons both during day time and night time (p > 0.05).

Table 4 Non dippers, dippers and risers among various seasons


Various studies have shown that cardiovascular morbidity and mortality is highest during cold weather [2, 4, 18]. Rates of myocardial infarction, stroke and sudden cardiac death are higher during winter as compared to summer season. In a large Canadian mortality database, there was 19% increased mortality from myocardial infarction and 20% increase in stroke mortality in January compared to September [18]. Similar findings have been observed from other studies reported among different latitudes, age groups and ethnicity. Excess cardiovascular morbidity and mortality during winter is attributed to increased sympathetic drive, hypercoagulable state, deranged blood lipid profile and hemoconcentration [2, 19]. Increase in BP on cold exposure is also considered a major contributor [2, 4].

A seasonal change in BP has been shown in various surveys from many developed countries specially those with temperate climate. The temperature excursion between seasons is different in temperate climate as compared to tropics. Hence results of these studies cannot be extrapolated to tropical countries.

This study shows a significant seasonal variation in MAP (24 h and DT), SBP and DBP (DT) between summer and winter. The difference in 24 h MAP was largely driven by the increase in day time pressures. There was no difference in night time MAP. Similarly, DBP and SBP during day time were significantly higher in winter compared to summer season. Intermediate values were observed in post monsoon and spring. BP tended to rise after summer in post monsoon.

These findings are consistent with the earlier reports. [10, 16, 20,21,22] The first large scale population based study was reported by Sega et al. which showed that 24 h average and day time blood pressure were higher in winter as compared to summer [10]. Similar findings were reported by Modesti et al. who reported that mean 24 h SBP and morning BP surge were significantly higher in cold days (133 ± 14 and 37 ± 9 mm HG) and lower in hot days (130 ± 14 and 33 ± 16 mm HG). As in our study they observed intermediate pressures during days with intermediate temperature (132 ± 14 and 35 ± 15 mm HG) [16]. We also had intermediate pressures during post monsoon and spring seasons. In another large study including 1395 subjects, only 24 h DBP was significantly higher in winters compared to summer [20]. There was no difference in 24 h SBP which is similar to our study. SBP (DT) and DBP (DT) were significantly higher which is in accordance with our study.

There are various mechanism of rise in BP with fall in temperature during winters [2]. Various physiological changes occur with falling temperature. This increased sympathetic activity resulting in rise in catecholamime levels causes arteriolar vasoconstriction and increased peripheral resistance. Increased aldosterone levels, endothelial dysfunction and decreased sweating are additional contributing factors [2, 3, 23, 24]. Reduced physical activity and weight gain during winters could also potentially lead to BP change. In our study, there was no significant variation in body weight with change in season.

Unlike day time BP, night time BP does not decrease during hot weather as seen in our and various other studies [16]. In fact, in a large study, isolated nocturnal hypertension was more common in summers compared to winters (15.2 vs 9.8%, p = 0.003). Non dipper were also more common in summer compared to winters (p < 0.001) [20]. This is similar to our study where non dipper were more common in summer season than winter season though statistically non significant.

Reasons for lack of fall in nocturnal BP are not fully understood. Alteration of sleep quality in hot weather has been postulated to affect the variation in nocturnal BP. Lack of variation may be due to better socioeconomic status of the subjects enroled. Maintenance of indoor temperature such as domestic air conditioning during summer and heaters during winter may negate the effect of weather on nocturnal BP. Other factors related to circadian rhythm may be involved and need further exploration.

Seasonal variations in BP have important implication for epidemiological studies on prevalence of hypertension in tropical climate [12, 5, 25]. Studies conducted in summer season are likely to show low prevalence of Hypertension. Seasonal variations should also be considered during diagnosis and management of Hypertension in routine clinical practice. Higher doses or number of drugs may be required in winter to achieve goal BP as compared to summer. Similarly anti-hypertensive therapy needs to be scaled down during summer. Lack in fall of BP during night is not observed in summer which may have important clinical implication. Decreasing anti-hypertensive therapy according to day time BP in summer may not control night time BP. This needs to be studied in large number of subjects specially those on anti-hypertensive therapy.

There are limitations in our study. These observations may not be applicable to the whole country since India is a large country and the seasonal variation of temperature in some parts is not so marked between summer and winter as in our region. Also, the humidity levels are significantly different between parts of our country. Another limitation is sample size which was restricted to 28 subjects. Twenty two subjects did not complete four seasons follow up due to non compliance. The temperature was obtained by local agency of national weather service. Temperature at the site of measurement may not be the same as measured in weather lab. Other weather lab parameters such as humidity, UV exposure and cloud free hours were not analysed.


The present study is the first study from India to evaluate seasonal change in ambulatory blood pressure. There are significant variations in blood pressure with change in season. The MAP (24 h and DT), SBP (DT) and DBP (DT) is significantly higher in winter as compared to summer season while intermediate values are observed in post monsoon and spring season. Increase in blood pressure is restricted to day time since night time BP did not show any significant seasonal variation between winter and summer. Further studies including a larger number of subjects are required to have better insight into the effect of season on blood pressure.


What is known about topic

  • Seasonal variation of blood pressure (BP) has been observed in both temperate and tropical countries.

  • Studies on seasonal variation in BP with ambulatory blood pressure monitoring (ABPM) are limited in number from tropical countries.

What this study adds

  • This is the first study from India which shows that there are significant seasonal variations in blood pressure as seen with ABPM.

  • The present study shows, there is a significant rise in mean arterial pressure (24 h and day time), systolic and diastolic blood pressure (day time) during winter as compared to summer.

  • There was no seasonal variation in night time BP between summer and winter and the seasonal difference was seen primarily in the day time BP.


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Correspondence to Gurpreet S. Wander.

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Goyal, A., Narang, K., Ahluwalia, G. et al. Seasonal variation in 24 h blood pressure profile in healthy adults- A prospective observational study. J Hum Hypertens 33, 626–633 (2019).

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