title: Incident invasive breast cancer, geographic location of residence, and reported average time spent outside.
abstract: There have been reports of greater breast cancer incidence and mortality at northern compared with southern latitudes postulated to be related to vitamin D exposure. Among 71,662 participants in the Women's Health Initiative Observational Study (WHIOS) free of cancer at baseline (1993-1998), associations were explored between incident invasive postmenopausal breast cancer (n = 2,535), over approximately 8.6 years follow-up, and the following: (a) region of residence at birth, age 15 years, age 35 years; (b) region of residence at WHIOS baseline; and (c) clinic center solar irradiance. Hazard ratios and 95% confidence intervals (CI) for breast cancer were estimated after adjustment for individual level confounders. There was no difference in breast cancer risk by region of earlier life, baseline residence, or solar irradiance measured in Langelys (gm-cal) per cm(2). There was an observed 15% decreased risk among women residing in areas of low versus high solar irradiance measured in Watts per m(2) (95% CI, 2-26%). However, the associated P(trend) of 0.20 was not significant. Conversely, women who reported spending on average <30 minutes versus >2 hours outside in daylight year round at WHIOS year 4 follow-up (n = 46,926), had a 20% (95% CI, 2-41%; P(trend) = 0.001) increased risk of breast cancer. In conclusion, region of residence and geographic solar irradiance are not consistently related to risk of breast cancer and may not be sufficient proxy measures for sunlight/vitamin D exposure. The observed association between time spent outside and breast cancer risk support the hypothesis that vitamin D may protect against breast cancer.
authors.affiliation: Department of Social and Preventive Medicine, School of Public Health and Health Professions, University at Buffalo, Buffalo, NY 14214-8001, USA. aemillen@buffalo.edu
authors.forename: Amy E
authors.initials: AE
authors.lastname: Millen
authors.forename: Mary
authors.initials: M
authors.lastname: Pettinger
authors.forename: Jo L
authors.initials: JL
authors.lastname: Freudenheim
authors.forename: Robert D
authors.initials: RD
authors.lastname: Langer
authors.forename: Carol A
authors.initials: CA
authors.lastname: Rosenberg
authors.forename: Yasmin
authors.initials: Y
authors.lastname: Mossavar-Rahmani
authors.forename: Christine M
authors.initials: CM
authors.lastname: Duffy
authors.forename: Dorothy S
authors.initials: DS
authors.lastname: Lane
authors.forename: Anne
authors.initials: A
authors.lastname: McTiernan
authors.forename: Lewis H
authors.initials: LH
authors.lastname: Kuller
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: Lopez
authors.forename: Jean
authors.initials: J
authors.lastname: Wactawski-Wende
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology*; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D015994:Incidence; D016014:Linear Models; D008875:Middle Aged; D017698:Postmenopause; D016016:Proportional Hazards Models; D012111:Residence Characteristics; D012307:Risk Factors; D013472:Sunlight; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology; D014807:Vitamin D / Q000008:administration & dosage
chemical_list: D014807:Vitamin D