Exploring the paradoxical association of sun exposure and melanoma-specific mortality: The Norwegian Women and Health (NOWAC) Study.
Level 3 - non-randomized controlled study
Prospective cohort study analyzing survival outcomes among incident melanoma cases
PubMed 42150442 · doi:10.1016/j.ejca.2026.116787
What was done
Researchers examined the prospective Norwegian Women and Health (NOWAC) cohort to evaluate associations between pre-diagnosis sun exposure and melanoma-specific as well as all-cause mortality. Among 2,234 patients with a first primary melanoma, hazard ratios were calculated using Cox regression. To test whether the observed protective effect of sun exposure is non-causal, they evaluated E-values for unmeasured confounding, computed bias-adjusted hazard ratios, and performed frailty analysis to model unobserved heterogeneity and selection bias from conditioning on melanoma diagnosis.
What was found
Over a mean follow-up of 8.0 years (311 total deaths, 168 melanoma-specific deaths), ever- versus never-sunburn was associated with reduced risk of melanoma-specific death (HR = 0.41, 95% CI: 0.24 to 0.68) and overall death (HR = 0.49, 95% CI: 0.33 to 0.72), with a significant negative trend across cumulative sunburns (p-trend ≤ 0.001). Sunbathing vacations were not significantly associated with melanoma-specific mortality (HR = 0.69, 95% CI: 0.37 to 1.27). While unmeasured confounding analyses showed minimal impact, frailty analysis indicated that selection bias partly explains the inverse association.
Why it matters
This study provides evidence that the paradoxical association between prior high sun exposure and improved melanoma survival is likely an artifact of selection bias (conditioning on diagnosis) rather than a causal, protective biologic effect.
Limits
The study included only Norwegian women, limiting generalizability to males and other geographic regions or skin phototypes. Pre-diagnosis sun exposure metrics relied on self-report. Conditioning on disease diagnosis introduces selection/collider bias that can distort causal inference.
Cited by
- context Chronic regular daily sun exposure is inversely associated with melanoma mortality across all published studies.
- contradicts Sunburning increases the risk of melanoma mortality.