Complete regression results for Table 2. Dependent variable: serum 25-hydroxyvitamin D (ng/ml)

Regression model	Model 1†	Model 2	Model 3	Model 4†	Model 5†
Description	UV index	UV index – quartiles	UV index – median	UV index groups	Interaction with obesity
Race/ethnicity (omitted: Non-Hispanic White)
Non-Hispanic Black	−7·47***	−7·49***	−7·87***	−7·96***	−8·01***
Hispanic	−3·41***	−3·38***	−3·39***	−3·37***	−3·32***
UV index
UV index 1 month before exam (continuous)
UV index 1 month before exam	0·51***				0·66***
Non-Hispanic Black×UV index	−0·09
BMI 25·0–30·0 kg/m2×UV index					−0·21
BMI ≥ 30·0 kg/m2×UV index					−0·28*
Quartiles of UV index 1 month before exam (omitted: Quartile 1)
Quartile 2		0·41
Quartile 3		1·45***
Quartile 4		1·27***
Non-Hispanic Black×quartile 2		−0·82
Non-Hispanic Black×quartile 3		−0·62
Non-Hispanic Black×quartile 4		−0·62
Half of UV index 1 month before exam (omitted: UV index <median)
UV index ≥median			1·15***
Non-Hispanic Black×UV index ≥median			−0·24
Groups of UV index 1 month before exam (omitted: 6–7)†
UV index<3				−3·15***
3 ≤ UV index<4				−2·50***
4 ≤ UV index<5				−2·23***
5 ≤ UV index<6				−0·88**
7 ≤ UV index<8				−0·02
UV index ≥8				0·39
Demographics
Age	−0·05***	−0·05***	−0·05***	−0·05***	−0·05***
Female	−0·26	−0·27	−0·27	−0·25	−0·30
Married	0·81***	0·83***	0·83***	0·81***	0·87***
Annual household income (omitted: <$US 25 000)
$US 25 000–34 999	0·16	0·15	0·14	0·17	0·20
≥$US 35 000	0·44*	0·42*	0·43*	0·44*	0·49*
Skin type
Hair colour (omitted: Black)
Red	1·78*	1·80*	1·80*	1·72*	1·84*
Blonde	2·25***	2·23***	2·25***	2·24***	2·30***
Light brown	2·10***	2·11***	2·12***	2·09***	2·12***
Medium brown	1·69***	1·66***	1·68***	1·67***	1·70***
Dark brown	1·11***	1·08***	1·11***	1·06***	1·17***
Other	2·65	2·79*	2·82*	2·68	2·70
Missing	2·07***	2·09***	2·11***	2·03***	2·08***
Skin reaction to 1/2 h of sun exposure without sunscreen or protective clothing (omitted: none)
Severe sunburn with blisters	−0·18	−0·18	−0·19	−0·18	−0·19
Severe sunburn for a few days with peeling	−0·21	−0·19	−0·18	−0·19	−0·24
Mildly burned with some tanning	0·91***	0·92***	0·92***	0·94***	0·94***
Turn darker without sunburn	0·51*	0·54*	0·54*	0·51*	0·51*
Other	−1·33	−1·32	−1·33	−1·27	−1·21
Missing	−0·59	−0·63	−0·62	−0·60	−0·49
Sun behaviours
How often stay in the shade on a sunny day, when outside for >1 h (omitted: sometimes)
Always	−1·95***	−1·93***	−1·94***	−2·01***	−2·17***
Most of the time	−1·69***	−1·68***	−1·68***	−1·72***	−1·77***
Rarely	2·03***	2·01***	2·00***	2·05***	2·09***
Never	1·46**	1·42**	1·42**	1·48**	1·53**
Don’t go in the sun	5·74	5·52	5·69	5·53	5·80
Missing	6·92***	6·85***	6·97***	6·81***	6·53***
Number of sunburns in past year (omitted: zero)
1	1·16***	1·17***	1·17***	1·14***	1·26***
2	0·87***	0·87***	0·87***	0·86***	0·93***
≥3	0·61***	0·61***	0·62***	0·61***	0·66***
Missing	5·13	5·08	5·10	4·91	5·50
How often wear a hat that covers face, ears and neck (omitted: never)
Always	0·50	0·50	0·51	0·52	0·32
Most of the time	−0·01	0·03	0·04	0·00	−0·03
Sometimes	0·23	0·25	0·26	0·27	0·24
Rarely	−0·61	−0·58	−0·58	−0·57	−0·61
How often wear a long-sleeved shirt (omitted: never)
Always	−1·85*	−1·88*	−1·88*	−1·79*	−1·60*
Most of the time	−2·09***	−2·14***	−2·18***	−2·05***	−1·95***
Sometimes	−0·49	−0·53	−0·53	−0·43	−0·48
Rarely	−0·93*	−0·93*	−0·94*	−0·91*	−0·82*
How often wear sunscreen (omitted: never)
Always	2·17	2·16	2·13	2·25	2·22
Most of the time	1·88	1·87	1·85	1·95	1·87
Sometimes	1·36	1·38	1·34	1·41	1·34
Rarely	0·13	0·12	0·09	0·22	0·11
Sunscreen SPF used most often (omitted: <15)
15–29	−0·45	−0·38	−0·36	−0·49	−0·53
≥30	−0·72	−0·67	−0·66	−0·75	−0·80
Missing	0·18	0·24	0·23	0·21	0·11
Missing data for hat, long-sleeved shirt, sunscreen
Missing	−10·54**	−10·39**	−10·54**	−10·14**	−10·49*
Other personal behaviours or characteristics
Vitamin D supplementation during past 30 d (avg. IU/d)	0·28***	0·28***	0·28***	0·28***	0·27***
Smoker
Every day	−1·26***	−1·23***	−1·23***	−1·28**	−1·15***
Some days	0·25	0·28	0·27	0·22	0·23
Missing	−0·33	−0·30	−0·31	−0·33	−0·34
BMI
BMI (kg/m2)	−0·28***	−0·28***	−0·28***	−0·28***
25·0–30·0 kg/m2					−0·27
≥30·0 kg/m2					−2·51***
Month/year of exam
Month (omitted: January)
February	−0·39	−0·32	−0·39	−0·42	−0·34
March	−1·11*	−0·97	−0·90	−1·25*	−1·16*
April	0·03	0·02	0·07	−0·39	0·15
May	−0·58	0·68	0·68	−1·25*	−0·50
June	0·44	2·00***	2·04***	−0·52	0·52
July	1·98**	3·16***	3·20***	1·33*	2·12***
August	2·19***	3·20***	3·24***	1·52**	2·25***
September	0·55	2·11***	2·22***	−0·27	0·64
October	0·44	1·96***	1·92***	−0·36	0·55
November	0·96	1·11*	1·16*	0·43	1·08*
December	1·23*	1·30*	1·38**	0·94	1·29*
Year (omitted: 2000)
2001–02	−1·63***	−1·63***	−1·67***	−1·43***	−1·64***
2003–04	−1·82	−1·96	−1·94	−1·83	−1·80
2005–06	−0·86	−1·04	−1·05	−0·79	−0·87
Intercept	30·60***	31·98***	32·16***	34·96***	23·49***
R 2	0·29	0·29	0·28	0·29	0·28
F	84·89	80·04	84·73	80·88	81·12
n	14 319	14 319	14 319	14 319	14 319

SPF, sun protection factor.

Robust standard errors were used.

*P<0·05, **P<0·01, ***P<0·001.

†Model presented in main article.