Association Between Sun Exposure and BMI in the Development of Nonmelanoma Skin Cancer
Exposure to the sun, whether cumulative or intermittent, is a known risk factor for the development of nonmelanoma skin cancer (NMSC). Past studies have found that greater body mass index (BMI) actually lessens the risk of women developing NMSCs. With this in mind, researchers sought to determine if the risk of NMSC with sun exposure was consistent across different BMIs and waist-to-hip ratios (WHRs). Their findings were published by Chan et al in Cancer.
Study Methods
The observational study included participants from the Women’s Health Initiative. The analysis included 71,645 postmenopausal women aged 50–79 between 1993 and 1998 from 40 U.S. sites.
All participants had a physical exam at study baseline and at 3 years, and a self-reported annual survey, completed at year 4, was used to gather information about sun exposure lifestyle factors. Questionnaire areas of focus were: physical activity, skin reaction to the sun, SPF used, and time spent outdoors during different stages of life. Body size was assessed using BMI and WHR. At the beginning of the study, 59% of participants were overweight as assessed by BMI and 49.2% were overweight as assessed by WHR.
Findings
The final analysis median follow-up was 11.93 years. A total of 13,351 (18.6%) study participants developed NMSC.
Participants with a BMI ≥ 25 kg/m2 showed a 22% lower risk of developing NMSC when compared to those with a BMI < 25 kg/m2 (main effect hazard ratio [HR] = 0.78, 95% confidence interval [CI] = 0.72–0.85). Over a 16-year follow-up period, this effect persisted, but the effect size was dependent on age—the protective BMI effect was greatest in women aged 50–59, was diminished in those aged 60–69, and was lost in those aged 70–79. Participants with WHRs ≥ 0.80 had an 11% lesser chance of developing NMSC (HR = 0.89, 95% CI = 0.82–0.96) compared to those with WHRs < 0.80.
Researchers then assessed how the NMSC hazard rate changed with sun exposure in relation to both BMI and WHR.
In women with a BMI ≥ 25 kg/m2 who had spent more than 2 hours outside per day had hazard rates of 1.28, 1.58, and 2.17 at regional ultraviolet (UV exposures) of 0.4–1.0, 1.4, and 1.5–1.9 W, respectively. In women with larger WHRs, a similar effect was seen—a significant interaction with sun exposure and langleys, a unit of heat transmission used to measure regional sun exposure in the study.
The authors concluded, “The results of this large prospective study show that women with a BMI ≥ 25 kg/m2 or a WHR ≥ 0.80 have lower hazard rates for NMSC. However, there is an interaction effect with sun exposure to also consider; compared with the normal-weight group, those in the overweight group have 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.
Disclosure: The study authors’ full disclosures can be found at onlinelibrary.wiley.com.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
