Table 3. Secondary outcomes at 30 days.

Values are numbers (percentages) unless stated otherwise.

Outcomes		30s Group (n = 700)	60s Group (n = 660)	90s Group (n = 680)	Control Group (n = 615)	Group difference P value#	Intervention/control difference P value##
Median (interquartile range) sickness absence (days)		0 (0)	0 (0)	0 (0)	0 (0)	0.544	0.648
Median (interquartile range) illness (days)		0 (0–3)	0 (0–3)	0 (0–3)	1 (0–4)	0.232	0.047
Completed (hot-to) cold shower protocol during first 30 days*		573 (82)	513 (79)	530 (79)	N.A.	0.138
Will to continue (hot-to) cold shower after first 30 days**		634 (93)	571 (89)	609 (91)	N.A.	0.024
Median (interquartile range) SF-36 physical component score		86.2 (78.8–91.4)	87.2 (80.5–91.2)	87.2 (79.8–91.4)	85.4 (77.8–90.4)	0.017	0.006
Median (interquartile range) SF-36 mental component score		84.7 (76.4–90.2)	85.1 (76.7–90.6)	85.7 (78–90.8)	83.9 (72.9–89.4)	0.003	0.001
Median (interquartile range) work engagement score		42 (33–46)	42 (33–46)	42 (34–47)	40 (32–46)	0.108	0.020
Median (interquartile range) anxiety score		1 (0–3)	1 (0–3)	1 (0–3)	1 (0–3)	0.003	0.001
Thermal body sensation**						0.160
	Warmer	262 (39)	265 (41)	269 (40)	N.A.
	Colder	55 (8)	72 (11)	69 (10)	N.A.
	No difference	363 (53)	304 (48)	333 (50)	N.A.
Thermal hands and feet sensation**						0.778
	Warmer	179 (26)	170 (26)	180 (27)	N.A.
	Colder	79 (12)	88 (14)	90 (13)	N.A.
	No difference	422 (62)	383 (60)	401 (60)	N.A.

This study investigated the effect of cold showering on health and work: a trial randomizing a (hot-to-) cold shower for 30, 60, 90 seconds or a control group during 30 consecutive days followed by 60 days of showering cold at their own discretion for the intervention groups.

N.A. Not applicable

* Missing data in 5, 8, 7 participants (respectively)

** Missing data in 20, 19, and 9 participants (respectively)

# Difference between all groups (Kruskal Wallis)

## Difference between all interventional groups versus control group (Mann-Whitney U)