Table 3.

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

Season	Variable	Unit, Category (Ref)	Model 1energy			Model 2energy
			Regression Coefficient	95%CI	p Value	Regression Coefficient	95%CI	p Value
Summer	VD intake	μg/1000kcal	1.10	(0.41, 1.79)	0.002	0.81	(0.083, 1.55)	0.029
	UV exposure energya	J/day	0.004	(0.0020, 0.0069)	0.001	0.004	(0.001, 0.007)	0.012
	Sex	women (vs men)	−5.52		<0.001	−5.80		<0.001
	Area	Kumamoto (vs Hokkaido)	−0.85		0.46	−1.41		0.23
	Age	years				0.12		0.005
	Smoking	past smoker (vs nonsmoker)				0.02		0.99
		current smoker (vs nonsmoker)				−1.01		0.51
	Skin typeb	III (vs II)				−0.51		0.69
		IV (vs II)				0.15		0.93
	Physical activityc	Mets x min				0.00		0.90
Winter	VD intake	μg/1000kcal	1.94	(1.29, 2.58)	<0.001	1.75	(1.13, 2.36)	<0.001
	UV exposure energy	J/day	0.005	(−0.004, 0.013)	0.29	0.004	(−0.005, 0.012)	0.37
	Sex	women (vs men)	−2.83		0.003	−2.66		0.007
	Area	Kumamoto (vs Hokkaido)	−1.53		0.10	−1.58		0.08
	Age	years				0.14		<0.001
	Smoking	past smoker (vs nonsmoker)				−0.72		0.53
		current smoker (vs nonsmoker)				0.61		0.63
	Skin typeb	III (vs II)				0.59		0.57
		IV (vs II)				−0.08		0.95

Confidence interval (CI); minutes (min); reference category (ref); vitamin D (VD); ultraviolet ray (UV); 25-hydroxyvitamin D₃ (25(OH)D₃); ^a UV exposure energy adjusted by exposed body surface area, irradiated body site, as well as sunscreen and sunshade clothing/tools use; ^b 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; ^c Physical activity level was estimated by the International Physical Activity Questionnaire (IPAQ) only in summer.