Table 3.
Association between vitamin D levels and skin type, sun exposure, diet, smoking, and socioeconomic status in mothers
| Season‐adjusted | Season + exposure + diet | All other variables | ||||||
|---|---|---|---|---|---|---|---|---|
| Factor | Levels | N | Difference | p | Difference | p | Difference | p |
| Mother—baseline 25OHD nmol/L | ||||||||
| Maternal age | Per year | 608 | 1.2 (0.8–1.7) | <.001 | 5 (0.1–1) | .022 | .3 (−.1–.8) | .151 |
|
Skin type |
I | 73 | Ref | .001 | Ref | .003 | Ref | <.001 |
| II | 182 | 14.9 (6.4–23.3) | 13 (5.3–20.7) | 11.5 (3.8–19.1) | ||||
| III | 310 | 17.3 (9.4–25.3) | 14.1 (6.8–21.4) | 13.8 (6.6–21) | ||||
| IV | 43 | 14.4 (2.7–26.1) | 13.8 (3.1–24.5) | 15.6 (4.9–26.3) | ||||
|
Mother time outside |
<15 min | 31 | Ref | .511 | Ref | .331 | Ref | .082 |
| 15–30 min | 185 | 9.9 (–2.1–21.9) | 6.5 (−4.4–17.3) | 7.3 (−3.4–18) | ||||
| 30 min–2 hrs | 316 | 8.2 (–3.4–19.9) | 5.9 (−4.7–16.4) | 7.6 (−2.8–18.1) | ||||
| >2 hrs | 76 | 9.9 (–3.3–23.1) | 8.7 (−3.2–20.7) | 12.4 (.5–24.3) | ||||
|
Travelled abroad |
No | 504 | Ref | <.001 | Ref | <.001 | Ref | .014 |
| Yes | 104 | 15.6 (9–22.3) | 10.7 (4.4–16.9) | 7.8 (1.6–14) | ||||
|
Maternal dietary Intake |
μg/day | 607 | 1.9 (.8–3.1) | .001 | 1.6 (0.5–2.6) | .005 | 1.4 (0.3–2.5) | .010 |
| Maternal supplements | No | 165 | Ref | <.001 | Ref | <.001 | Ref | <.001 |
| Yes | 443 | 27.9 (22.7–33.1) | 26.5 (21.4–31.7) | 23.4 (18.1–28.8) | ||||
| Maternal Total intake | μg/day | 607 | 2.6 (2.1–3) | <.001 | 2.4 (2–2.9) | <.001 | 2.2 (1.7–2.6) | <.001 |
|
Smoker |
No | 543 | Ref | <.001 | Ref | .013 | Ref | .029 |
| Yes | 65 | –18.5 (–26.4–10.5) | −9.7 (−17.4–2.1) | −8.5 (−16.1–.8) | ||||
|
IMD quintile |
1st | 38 | Ref | <.001 | Ref | .031 | Ref | .118 |
| 2nd | 72 | 5.3 (–6.8–17.4) | 7.2 (−3.8–18.3) | 8 (−3–19) | ||||
| 3rd | 105 | –.2 (–11.6–11.2) | 2.7 (−7.7–13.2) | 3.2 (−7.2–13.6) | ||||
| 4th | 127 | –1.4 (–12.5–9.8) | 2.1 (−8.1–12.4) | 3.4 (−6.8–13.6) | ||||
| 5th | 257 | –10.5 (–21–.1) | −2.8 (−12.5–6.9) | −.8 (−10.6–9) | ||||
| Mother—4 months 25OHD nmol/L | ||||||||
| Maternal age | Per year | 333 | .5 (0–.9) | .058 | .1 (−.3–.5) | .651 | −.1 (−.5–.4) | .809 |
|
Skin type |
I | 43 | Ref | .002 | Ref | <.001 | Ref | <.001 |
| II | 109 | 10.8 (3.1–18.5) | 10.5 (3.5–17.5) | 10.9 (3.9–17.9) | ||||
| III | 162 | 15.5 (8.2–22.9) | 15.1 (8.5–21.8) | 16 (9.3–22.7) | ||||
| IV | 19 | 7.9 (–3.8–19.7) | 8.5 (−2.2–19.2) | 11.1 (.2–22) | ||||
|
Infant time outside |
<15 min | 10 | Ref | .013 | Ref | .014 | Ref | .018 |
| 15–30 min | 80 | 4.5 (–10–19) | 3.1 (−10.3–16.5) | 1.9 (−11.4–15.2) | ||||
| 30 min–2 hrs | 193 | –5 (–19–9.1) | −5.3 (−18.2–7.7) | −5.7 (−18.6–7.1) | ||||
| >2 hrs | 45 | –4.3 (–19.6–11.1) | −4.7 (−18.9–9.4) | −5.6 (−19.7–8.4) | ||||
| Travelled abroad | No | 291 | Ref | <.001 | Ref | <.001 | Ref | <.001 |
| Yes | 38 | 15.3 (7.4–23.2) | 14.7 (7.3–22) | 14.1 (6.7–21.4) | ||||
| Maternal dietary intake | μg/day | 329 | 1 (–.1–2.2) | .069 | .9 (−.1–1.9) | .081 | .9 (−.1–1.9) | .09 |
| Maternal supplements | No | 193 | Ref | <.001 | Ref | <.001 | Ref | <.001 |
| Yes | 137 | 15.5 (10.9–20.1) | 14.3 (9.8–18.7) | 13.8 (9.2–18.3) | ||||
| Maternal Total intake | μg/day | 329 | 1.4 (1–1.8) | <.001 | 1.3 (0.9–1.7) | <.001 | 1.3 (.9–1.7) | <.001 |
|
Smoker |
No | 297 | Ref | <.001 | Ref | .003 | Ref | .006 |
| Yes | 32 | –15.6 (–23.6–7.7) | −11.3 (−18.6–3.9) | −10.7 (−18.3–3.1) | ||||
|
IMD quintile |
1st | 26 | Ref | .069 | Ref | .159 | Ref | .377 |
| 2nd | 44 | .4 (–10.3–11.1) | 4.8 (−5.1–14.7) | 4.4 (−5.5–14.2) | ||||
| 3rd | 60 | .2 (–10–10.3) | .8 (−8.5–10.1) | .4 (−8.9–9.6) | ||||
| 4th | 69 | –4.3 (–14.2–5.7) | −3 (−12.2–6.1) | −2.8 (−11.9–6.3) | ||||
| 5th | 128 | –5 (–14.3–4.4) | −1.5 (−10–7.1) | −.3 (−8.9–8.3) | ||||
Effects are expressed as differences from the reference level (ref) for categorical variables or per unit for continuous variables with a 95%CI as estimated from a linear regression model. Significance tests are for a linear trend over the categories or values. Three models are shown, first are adjusted only for season using a sinusoidal model; second are adjusted for the exposure and dietary variables and; third are adjusting for all the other variables listed in the table. Note that this final model overadjusts due to the correlations between socioeconomic and exposure and dietary variables