Table 1 Baseline characteristics of overall study participants and according to frequency of sauna bathing
Characteristics | Â | 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) | Â | |
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 |