Interaction of body mass index or waist‐to‐hip ratio and sun exposure associated with nonmelanoma skin cancer: A prospective study from the Women’s Health Initiative

• Published in: Cancer Vol. 125; no. 7; pp. 1133 - 1142
• Main Authors: Chan, Alfred A., Noguti, Juliana, Pak, Youngju, Qi, Lihong, Caan, Bette, Going, Scott, Han, Jiali, Chlebowski, Rowan T., Lee, Delphine J.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01-04-2019
• Subjects: Aged; Body mass; Body Mass Index; body mass index (BMI); Body size; Body weight; Cancer; Carcinoma, Basal Cell - epidemiology; Carcinoma, Squamous Cell - epidemiology; Environmental Exposure - statistics & numerical data; Exposure; Female; Health hazards; Health risk assessment; Hip; Humans; Incidence; Middle Aged; nonmelanoma skin cancer (NMSC); Obesity; Obesity - epidemiology; Oncology; Overweight; Overweight - epidemiology; Pathogenesis; Post-menopause; postmenopausal women; Proportional Hazards Models; Risk analysis; Risk factors; Skin cancer; Skin Neoplasms - epidemiology; Sun; sun exposure; Sunlight; ultraviolet; United States - epidemiology; Vitamin D; Waist-Hip Ratio; waist‐to‐hip ratio (WHR); Womens health; Women’s Health Initiative; United States; skin cancer; Women’s Health Initiative; postmenopausal women; ultraviolet; body mass index (BMI); sun exposure; nonmelanoma skin cancer (NMSC); overweight; waist-to-hip ratio (WHR); obesity
• ISSN: 0008-543X; 1097-0142
• DOI: 10.1002/cncr.31810

Background
The incidence of nonmelanoma skin cancer (NMSC) exceeds the incidence of all other types of cancers combined. Cumulative sun exposure and intermittent sun exposure are known risk factors for the development of NMSC. Because obesity has been shown to decrease the risk of NMSC incidence, this study investigated whether the risk of NMSC with sun exposure was consistent across different levels of body size.
Methods
Body size was assessed with the body mass index (BMI) and the waist‐to‐hip ratio (WHR). Sun exposure was assessed in watts and langleys and by the amount of time spent outdoors per day in the summer during a person’s 30s.
Results
Among 71,645 postmenopausal women eligible for inclusion in this study, 13,351 participants (18.6%) developed NMSC. A BMI ≥ 25 kg/m2 or a WHR ≥ 0.80 was associated with lower NMSC hazard rates (hazard ratio for BMI, 0.78; hazard ratio for WHR, 0.89); however, the association between higher levels of sun exposure and a higher risk of NMSC was more apparent among women with a BMI ≥ 25 kg/m2 or a WHR ≥ 0.80 in comparison with those of a normal weight (P for interaction for BMI < .001; P for interaction for WHR = .022).
Conclusions
Although most studies have considered sun exposure as a covariate, none have addressed the potential interaction of body size with sun exposure; therefore, the effect size of being overweight or obese may have been overestimated. In comparison to the normal‐weight group, those in the overweight group had increasingly higher hazard rates with increasing sun exposure. Further studies are warranted to investigate how increased weight interacts with sun exposure to influence skin cancer pathogenesis.
Although most studies have considered sun exposure as a covariate, none have addressed the potential interaction of body size with sun exposure; therefore, the effect size of obesity in reducing the risk of nonmelanoma skin cancer incidence may have been overestimated. This study finds that, in comparison with women of normal weight, an overweight group has increasingly higher hazard rates with increasing sun exposure.