. 2020 Mar 11;12(3):743. doi: 10.3390/nu12030743

Table 2.

Relationship between dietary vitamin D intake, UV exposure time and serum 25(OH)D₃ concentration by season among Japanese adults (n = 107).

Season	Variable	Unit, Category (Ref)	Model 1_time			Model 2_time
Season	Variable	Unit, Category (Ref)	Regression Coefficient	95%CI	p Value	Regression Coefficient	95%CI	p Value
Summer	VD intake	μg/1000kcal	1.00	(0.34, 1.67)	0.004	0.88	(0.14, 1.62)	0.020
	UV exposure time	min	0.059	(0.034, 0.083)	<0.001	0.047	(0.014, 0.079)	0.005
	Sex	women (vs men)	−5.94		<0.001	−5.39		0.001
	Area	Kumamoto (vs Hokkaido)	0.34		0.77	−0.17		0.90
	Age	years				0.08		0.08
	Smoking	past smoker (vs nonsmoker)				−0.12		0.93
		current smoker (vs nonsmoker)				−0.76		0.62
	Skin type^a	III (vs II)				−0.46		0.71
		IV (vs II)				0.25		0.87
	Sunscreen use^b	user (vs nonuser)				−1.67		0.29
	Sunshade clothing/tools use^c	user (vs nonuser)				0.53		0.70
	Physical activity^d	Mets x min				0.00		0.93
Winter	VD intake	μg/1000kcal	1.88	(1.25, 2.52)	<0.001	1.70	(1.09, 2.32)	<0.001
	UV exposure time	min	0.067	(0.0097, 0.125)	0.022	0.041	(−0.016, 0.099)	0.16
	Sex	women (vs men)	−2.65		0.005	−1.90		0.10
	Area	Kumamoto (vs Hokkaido)	−1.05		0.26	−0.73		0.45
	Age	years				0.12		0.001
	Smoking	past smoker (vs nonsmoker)				−0.92		0.42
		current smoker (vs nonsmoker)				0.61		0.63
	Skin type^a	III (vs II)				0.42		0.69
		IV (vs II)				−0.27		0.83
	Sunscreen use^b	user (vs nonuser)				−1.27		0.33
	Sunshade clothing/tools use^c	user (vs nonuser)				1.11		0.24

Confidence interval (CI); minutes (min); reference category (ref); vitamin D (VD); ultraviolet ray (UV); 25-hydroxyvitamin D₃ (25(OH)D₃); ^a Fitzpatrick skin type was self-reported. The classification was made by erythema and tanning reactions to first exposure to sunlight in summer. II: usually burn, tan less than average, III: sometimes mildly burn, tan about average, IV: rarely burn, tan more than average; ^b Nonuser means those who did not use sunscreen at all. Those who used sunscreen on any body surface were considered users; ^c Those who used any or all of hat, parasol, and gloves. The others were considered nonusers; ^d Physical activity level was estimated by the International Physical Activity Questionnaire (IPAQ) only in summer.