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J Breast Cancer. 2013 Jun;16(2):171-177. English. Original Article.
Wu SH , Ho SC , So E , Lam TP , Woo J , Yuen PY , Qin L , Ku S .
School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China.
Division of Epidemiology, Department of Medicine, Institute of Medicine and public Health, Vanderbilt University Medical Center, Nashville, USA.
Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Hong Kong, China.
Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Hong Kong, China.
Physical Education Unit, The Chinese University of Hong Kong, Hong Kong, China.

PURPOSE: This study aims to assess the association of sunlight exposure with breast cancer risk, measured by the breast density assessed from Tabar's mammographic pattern in Chinese women. METHODS: A total of 676 premenopausal women were recruited to participate in this study, in which 650 completed a validated sunlight exposure questionnaire via telephone. The mammograms were classified according to Tabar's classification for parenchyma, and patterns IV & V and I, II & III indicated respectively high and low risk mammographic patterns for breast cancer. The odds ratios (OR) and 95% confidence intervals (CIs) for sun exposure-related variables were estimated using unconditional logistic regression with adjustment for potential confounders. RESULTS: Among 646 participants, women with high breast cancer risk (Tabar's patterns IV &V) had less hours spent in the sun than those with low risk (I, II & III) at any age stage. A higher level of sunlight exposure was associated with a significantly lower risk having high risk Tabar's pattern. Women aged 40 to 44 years who were in the highest tertile of lifetime total hours spent in the sun had a multi-adjusted OR of 0.41 (95% CI, 0.18-0.92; p for trend=0.03) compared with those in the lowest tertile (>2.19 hr/day vs. <1.32 hr/day). For hours spent in the sun across the ages of 6 to 12 years, the comparable OR was 0.37 (95% CI, 0.15-0.91; p for trend=0.03). CONCLUSION: These findings suggest that higher sunlight exposure is related to a lower risk of having high risk breast density pattern in premenopausal women. Our results also suggest the most relevant period of exposure is during earlier life.

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