Table 2.

Seasonal characteristics and behaviours of the study population: female, premenopausal, shift-working nurses (n 83), Kingston, Ontario, Canada, April 2008 to July 2009

	Summer/autumn (n 74)		Winter/spring (n 70)
Seasonal characteristic/behaviour	Mean or n	sd or %	Mean or n	sd or %
Serum 25(OH)D* (nmol/l)
Summer/autumn (median 87·4 nmol/l)	93·8	42·2	–	–
Winter/spring (median 69·9 nmol/l)	–	–	73·9	26·0
Vitamin D status
Deficient (serum 25(OH)D < 30 nmol/l)	3	4	4	6
Inadequate (30 ≤ serum 25(OH)D < 50 nmol/l)	4	5	5	7
Adequate (serum 25(OH)D ≥ 50 nmol/l)	67	91	61	87
Lifestyle factors (previous 6 months)
Supplement use (including cod liver oil)
Yes	32	43	29	42
No	42	57	40	58
Time spent outdoors on work days
<1 h/d	58	78	–	–
1–3 h/d	16	22	–	–
Time spent outdoors on days off
≤2 h/d	35	47	–	–
>2 h/d	39	53	–	–
Time spent outdoors 11.00–15.00 hours
<1 h/d	22	57	–	–
1–2 h/d	42	14	–	–
≥2 h/d	10	30	–	–
Sunscreen use
<50 % of times outdoors	50	68	–	–
≥50 % of times outdoors	14	19	–	–
Always	10	14	–	–
Tanning bed use†
Yes	19	26	20	29
No	55	74	49	70
Took a sunny vacation†‡
Yes	11	15	29	42
No	63	85	40	58

25(OH)D, 25-hydroxyvitamin D.

*Serum 25(OH)D data presented as mean and standard deviation; all other data presented as number and percentage.

†Frequency of tanning bed use ranged from once per week to a few times in 6 months.

‡Sunny vacation durations ranged from 6 to 18 d in length during the summer/autumn and from 6 to 28 d in length during the winter/spring.