Sunlight exposure during formative years protects against breast cancer risk

People with increased sun exposure during their adolescence and early adulthood appear to have a lower risk of breast cancer, as suggested in a population-based case-control study from Iran.

The study included 600 participants with newly diagnosed breast cancer and 600 population controls ages 18–75 years. Researchers used disaggregated data for sunlight exposure (hours/day) as follows: adolescence (10–20 years), early adulthood (20–30 years), after 30 years, and lifetime exposure, as assessed in summer and winter.

In multivariable logistic regression models, each hourly increase in sunlight exposure during adolescence was associated with an 11-percent to 16-percent reduction in the odds of breast cancer (exposure during winter: odds ratio [OR], 0.84, 95 percent confidence interval [CI], 0.78–0.91; exposure during summer: OR, 0.89, 95 percent CI, 0.83–0.96). No associations were observed for sunlight exposure after the age of 30 years.

However, lifetime sunlight exposure showed a protective association with the odds of breast cancer. Each additional hour of sunlight exposure per day lowered the odds by 16 percent in winter (OR, 0.84, 95 percent CI, 0.76–0.93) and by 9 percent in summer (OR, 0.91, 95 percent CI, 0.82–1.00).

A dose–response association was observed for both adolescence and lifetime sunlight exposure and the odds of breast cancer.

These findings underscore the need for public health strategies that promote moderate sunlight exposure during critical life stages.