Table 1.

Characteristics of participants included in vitamin D and genetic substudies (Sister Study, 2003–2009)

CharacteristicsRandom subcohort (n = 1,829); N (%)Breast cancer casesa (n = 1,601); N (%)
Age at blood draw; mean (SD)55.3 (8.9)57.4 (8.9)
Total 25(OH)D level; mean (SD)31.8 (10.5)31.0 (10.1)
Total 25(OH)D >38 ng/mL460 (25)330 (21)
Race/ethnicity
 Non-Hispanic white1,576 (86)1,365 (85)
 Non-Hispanic black134 (7)122 (8)
 Hispanic81 (4)63 (4)
 Other38 (2)50 (3)
Education level
 High school or less292 (16)245 (15)
 Some college639 (35)514 (32)
 Bachelor's degree468 (26)421 (26)
 Graduate degree430 (24)420 (26)
Menopausal status
 Premenopausal613 (34)461 (29)
 Postmenopausal1,216 (66)1,140 (71)
Current BMI
 <25.0 kg/m2702 (38)582 (36)
 25–29.9 kg/m2581 (32)506 (32)
 ≥30 kg/m2543 (30)513 (32)
Current hormonal birth control use
 Yes75 (4)66 (4)
 No1,750 (96)1,531 (96)
Current hormone therapy use
 Current, estrogen plus progestin65 (4)84 (5)
 Current, unopposed estrogen125 (7)133 (8)
 No current use1,634 (90)1,379 (86)
Physical activity (in last year)
 0–1 hours/week635 (35)539 (34)
 1.1–3 hours/week557 (30)516 (32)
 >3 hours/week637 (35)546 (34)
Alcohol consumption in last year
 Never/former drinker341 (19)300 (19)
 Current drinker, <1 drink/day1,230 (67)1,069 (67)
 Current drinker, ≥1 drink/day253 (14)231 (14)
Parity
 0 births339 (19)295 (18)
 1 birth276 (15)235 (15)
 2 births664 (36)576 (36)
 ≥3 births549 (30)495 (31)
History of osteoporosis
 Yes431 (24)343 (21)
 No1,397 (76)1,258 (79)
Regular vitamin D supplement use (≥4 times/week)
 None840 (47)731 (46)
 Multivitamin, no extra vitamin D732 (41)657 (42)
 Multivitamin and vitamin D131 (7)122 (8)
 Vitamin D and calcium76 (4)54 (3)
 Vitamin D only10 (1)9 (1)
Family history of breast cancer
 Affected sister or half-sister only1,359 (74)1,047 (65)
 >1 first-degree relative470 (26)554 (35)
  • NOTE: Missing values: Race (1 case), education (1 case), current BMI (3 in subcohort), current hormonal birth control use (4 in subcohort, 4 cases), current hormone therapy use (5 in subcohort, 5 cases), alcohol (5 in subcohort, 1 case), parity (1 in subcohort), osteoporosis (1 in subcohort), supplement use (40 in subcohort, 28 cases).

  • aIncludes 67 women also selected as part of subcohort.