Table 6:

Effect modification by clinical characteristics, demographics, and medical history on season-adjusted change in serum 25(OH)D concentrations from baseline to 1-year ^a,b

Characteristics included as effect modifiers:	N	Beta (SE)	95% CI	p-value	p-value interaction
Age categories					0.1014
< 65 years	782	13.44 (0.51)	(12.4, 14.4)	<.0001
65 - <75	667	11.85 (0.55)	(10.8, 12.9)	<.0001
75+	174	12.92 (1.08)	(10.8, 15.0)	<.0001
Gender					0.007
Male	791	11.75 (0.51)	(10.8, 12.7)	<.0001
Female	832	13.67 (0.49)	(12.7, 14.6)	<.0001
Race/Ethnicity					0.001
Non-Hispanic white	1133	11.99 (0.42)	(11.2, 12.8)	<.0001
African American	287	15.66 (0.84)	(14.0, 17.3)	<.0001
Hispanic	94	12.12 (1.47)	(9.2, 15.0)	<.0001
Other	70	13.87 (1.72)	(10.5, 17.2)	<.0001
BMI categories at 1-year					0.102
<25 kg/m2	460	13.98 (0.66)	(12.7, 15.3)	<.0001
25 - <30 kg/m2	614	12.50 (0.57)	(11.4, 13.6)	<.0001
30+ kg/m2	490	12.14 (0.64)	(10.9, 13.4)	<.0001
Non-randomized vitamin D supplement use at 1-year					<.0001
None	878	14.64 (0.47)	(13.7, 15.6)	<.0001
≤400 IU/day	308	10.71 (0.75)	(9.2, 12.2)	<.0001
401-800 IU/day	357	11.00 (0.80)	(9.4, 12.6)	<.0001
>800 IU/day	80	7.55 (1.58)	(4.5, 10.7)	< 0.001
Compliance at 1-year					0.0001
<2/3 of study pills or non-rand Vitamin D>800 IU/day	113	7.69 (1.34)	(5.10, 10.3)	<.0001
≥2/3 of study pills & non-rand Vitamin D≤800 IU/day	1510	13.11 (0.37)	(12.4, 13.8)	<.0001
25(OH)D level at baseline					<.0001
<20 ng/mL	268	17.31 (0.89)	(15.6, 19.0)	<.0001
20 – 29.9 ng/mL	549	12.19 (0.62)	(11.0 . 13.4 )	<.0001
≥30 ng/mL	806	11.38 (0.51)	(10.4, 12.4)	<.0001

^aMain multivariable linear regression model contains all covariates listed in table 4. One variable of interest (e.g. gender, race/ethnicity, etc.) and an interaction term with vitamin D randomized treatment were (one at a time) additionally included in the model.

^bNo significant interaction for alcohol consumption, smoking, diabetes, hypertension, or medication use.