Table 1 Factors contributing to predictors of age-adjusted plasma 25(OH)D level from a multiple linear regression model of 1095 men in the Health Professionals Follow-Up Study (Giovannucci et al, 2006)

From: Prospective study of predictors of vitamin D status and survival in patients with colorectal cancer

Factor

Change in 25(OH)D (ng ml−1)

Intercept

33.81

Race

 White

0 (referent)

 African American

−5.31

 Asian

−5.49

 Other

−0.17

Residence

 Northeast/Mid-Atlantic

0 (referent)

 Midwest/West

+1.61

 South

+2.56

Quintile of leisure-time physical activity (MET-hr per week) a

 5

0 (referent)

 4

−1.81

 3

−3.07

 2

−3.59

 1

−5.40

Body mass index (kg m−2)

 <22

0 (referent)

 22–24.9

−0.40

 25–29.9

−1.80

 30–34.9

−2.58

 ⩾35

−3.44

Dietary vitamin D (IU per day)

 ⩾400

0 (referent)

 300–399

−1.39

 200–299

−1.04

 100–199

−2.85

 <100

−4.16

Supplementary vitamin D (IU per day) b

 ⩾400

0 (referent)

 200–399

−0.71

 1–199

+0.97

 <1

−0.83

Season of blood draw c

 Autumn (September, October, and November)

0 (referent)

 Summer (June, July, and August)

−0.74

 Spring (March, April, and May)

−4.83

 Winter (December, January, and February)

−5.42

  1. Abbreviations: 25(OH)D=25-hydroxyvitamin D3; hr=hour; IU=international units; MET=metabolic equivalents.
  2. aPhysical activity is used as a proxy for outdoor activities, which will tend to increase solar UV-B exposure.
  3. bNot statistically significant.
  4. cSeason of blood draw was adjusted but not used in the predictive model because season is a strong determinant of 25(OH)D level and reflects the time of blood draw, but it is not a factor in determining long-term average between-person variation in 25(OH)D level.
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