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Table 1 Baseline characteristics of overall study participants and according to frequency of sauna bathing

From: Sauna bathing is associated with reduced cardiovascular mortality and improves risk prediction in men and women: a prospective cohort study

Characteristics   Frequency of sauna bathing (times per week)
Overall (N = 1688) 1 (n = 455) 2–3 (n = 1028) 4–7 (n = 205) P value for heterogeneity
Mean (SD) or n (%) or median (IQR) Mean (SD) or n (%) or median (IQR) Mean (SD) or n (%) or median (IQR) Mean (SD) or n (%) or median (IQR)  
Sauna use
 Temperature, °C 75.9 (9.9) 77.4 (9.4) 75.4 (9.7) 74.8 (10.9) < 0.001
 Duration, minutes/sauna session, median (IQR) 13 (10–15) 10 (10–15) 15 (10–20) 13 (10–15) 0.073
 Duration, minutes/week, median (IQR) 30 (15–40) 10 (10–15) 30 (20–40) 60 (40–90) < 0.001
Demographics
 Age, years 63 (7) 64 (7) 63 (6) 60 (6) < 0.001
 Male, n (%) 821 (48.6) 177 (38.9) 512 (49.8) 132 (64.4) < 0.001
 Body mass index, kg/m2 27.9 (4.4) 27.4 (4.4) 28.1 (4.4) 28.2 (4.6) 0.013
 Systolic blood pressure, mmHg 136 (17) 137 (18) 136 (17) 135 (17) 0.356
 Diastolic blood pressure, mmHg 81 (9) 81 (9) 81 (9) 82 (10) 0.259
 Alcohol consumption, g/week, median (IQR) 12.20 (1.00–53.68) 8.75 (0.32–45.11) 12.53 (1.29–53.34) 24.00 (3.20–76.60) 0.004
 Smokers, n (%) 221 (13.1) 70 (15.4) 132 (12.8) 19 (9.3) 0.091
 Smoking, pack years* 3.05 (10.3) 3.7 (11.4) 2.9 (10.1) 2.1 (8.3) 0.174
 Total physical activity per week, h, median (IQR) 7.94 (4.60–13.21) 7.31 (4.16–12.05) 8.21 (4.80–13.21) 8.48 (4.78–14.76) 0.029
 Physical activity, MET h/year, median (IQR) 1817 (1077–2992) 1625 (948–2703) 1874 (1109–3055) 2012 (1256–3296) < 0.001
 Energy expenditure of physical activity, kcal/day, median (IQR) 383 (224–598) 325 (186–512) 399 (237–610) 449 (293–723) < 0.001
 Mean intensity of physical activity, METs 4.58 (1.02) 4.43 (1.02) 4.61 (1.02) 4.76 (1.03) < 0.001
 Energy intake, kJ/day 7612 (2397) 7146 (2263) 7688 (2393) 8250 (2524) < 0.001
 Previous myocardial infarction, n (%) 118 (7.0) 34 (7.5) 70 (6.8) 14 (6.8) 0.895
 History of coronary heart disease, n (%) 474 (28.1) 128 (28.1) 289 (28.1) 57 (27.8) 0.996
 Type 2 diabetes, n (%) 138 (8.2) 45 (9.9) 80 (7.8) 13 (6.3) 0.233
 Hypertension, n (%) 702 (41.6) 196 (43.1) 421 (41.0) 85 (41.5) 0.746
 Serum LDL cholesterol, mmol/L 3.59 (0.93) 3.56 (0.95) 3.61 (0.93) 3.59 (0.87) 0.598
 Serum HDL cholesterol, mmol/L 1.25 (0.31) 1.26 (0.33) 1.24 (0.30) 1.26 (0.33) 0.356
 Fasting blood glucose, mmol/L 5.1 (1.2) 5.1 (1.3) 5.1 (1.2) 5.1 (1.2) 0.985
Socioeconomic and living condition characteristics
 Socioeconomic status, unit 10.9 (4.7) 10.3 (4.7) 11.3 (4.7) 10.3 (4.5) < 0.001
 Annual income (1998–2001), € 16,144 (11,715) 16,970 (10,474) 15,337 (10,703) 18,377 (17,403) 0.001
 Academic degree (college or university), n (%) 93 (5.5) 47 (10.3) 40 (3.9) 6 (2.9) < 0.001
 Daily working time (duration), h 8.1 (1.8) 7.9 (1.7) 8.1 (1.7) 8.7 (2.4) < 0.001
 Physical strain of work, unit 2.40 (0.88) 2.35 (0.89) 2.42 (0.87) 2.43 (0.87) 0.402
 Mental strain at work, unit 2.47 (0.69) 2.47 (0.72) 2.46 (0.68) 2.50 (0.68) 0.748
 Type of residence, n (%)      < 0.001
  Family house 825 (48.9) 106 (23.4) 574 (55.8) 145 (70.7)  
  Attached house 219 (13.0) 75 (16.5) 123 (12.0) 21 (10.2)  
  Apartment house 643 (38.1) 273 (60.1) 331 (32.2) 39 (19.0)  
 Summer cottage (own available), n (%) 804 (47.8) 190 (41.9) 512 (50.1) 102 (49.8) 0.013
  1. Complete baseline information was available on 1688 individuals
  2. IQR interquartile range, SD standard deviation, LDL low-density lipoprotein, HDL high-density lipoprotein
  3. *Pack-years denotes the lifelong exposure to smoking which was estimated as the product of years smoked and the number of tobacco products smoked daily at the time of examination
  4. Physical activity was computed by multiplying the duration and intensity of each physical activity by body weight. Physical activity was assessed using the 12-month physical activity questionnaire
  5. Socio-economic status is a summary index that combines measures of income, education, occupation, occupational prestige, material standard of living, and housing conditions, all of which were assessed with self-reported questionnaires