Baseline age-adjusted characteristics of NHS and NHSII study participants according to category of UV-B*
| NHS in 1976 (n=106368) | NHSII in 1989 (n=115561) | |||||
|---|---|---|---|---|---|---|
| Low UV-B (n=41 305) | Medium UV-B (n=43 227) | High UV-B (n=21 836) | Low UV-B (n=35 808) | Medium UV-B (n=31 755) | High UV-B (n=47 998) | |
| Age in years, mean (SD) | 42.4 (7.2) | 42.2 (7.3) | 44.1 (7.0) | 34.5 (4.7) | 35.1 (4.6) | 34.9 (4.6) |
| Caucasian (%) | 94 | 95 | 92 | 93 | 96 | 90 |
| BMI, mean (SD) (kg/m2) | 23.7 (4.1) | 23.8 (4.2) | 23.4 (4.0) | 24.1 (5.0) | 24.4 (5.2) | 23.9 (5.0) |
| Never smoker (%) | 40 | 45 | 47 | 60 | 66 | 68 |
| Pack-years, mean (SD)† | 11.2 (14.8) | 9.7 (14.1) | 10.0 (15.1) | 4.6 (7.8) | 3.8 (7.1) | 3.5 (7.0) |
| Physical activity, mean (SD), MET-hours/week | 14.4 (22.1) | 13.6 (19.7) | 14.8 (21.5) | 26.0 (38.2) | 23.8 (35.3) | 24.8 (36.9) |
| Vitamin D intake ≥400IU/day‡ (%) | 28 | 28 | 31 | 40 | 36 | 38 |
| Nulliparous, % | 7 | 7 | 9 | 31 | 27 | 32 |
| Total breast feeding ≥12 months§ (%) | 14 | 14 | 15 | 21 | 22 | 20 |
| Premenopausal (%) | 74 | 73 | 66 | 98 | 97 | 96 |
| Alcohol, mean (SD) (grams/day) | 6.9 (10.5) | 5.4 (9.7) | 7.8 (12.1) | 3.3 (6.0) | 2.7 (5.5) | 3.3 (6.5) |
| Husband's education >college (%) | 16 | 13 | 18 | 24 | 21 | 23 |
| Median income <US$42000 (%) | 11 | 17 | 20 | 11 | 18 | 20 |
All variables (except age) are standardised to the age distribution of the population in 1976 (NHS) and 1989 (NHSII). Means with SD or percentages are shown.
*Low: ≤109 Robertson–Berger units×10−4 (R-B), medium: >109 to ≤117 R-B, high: >117 R-B.
†Among ever-smokers only.
‡Vitamin D intake from diet and supplements adjusted for energy intake in international units (IU) per day.
§Among parous women only.
BMI, body mass index; MET, metabolic equivalent; NHS, Nurses’ Health Study; NHSII, Nurses’ Health Study II; UV-B, ultraviolet-B.