Table 1.
Baseline characteristics of overall study participants and according to frequency of sauna bathing
| 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 |
Complete baseline information was available on 1688 individuals
IQR interquartile range, SD standard deviation, LDL low-density lipoprotein, HDL high-density lipoprotein
*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
†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
‡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