The Montréal (Canada) study examining seasonal variation in prostate cancer aggressiveness presents intriguing epidemiological data that deserve both recognition and critical scrutiny.1 The authors assembled an impressive cohort of 3747 patients spanning 28 years, providing substantial statistical power. The 23% reduction in primary Gleason scores 4–5 during quarter 4 (Q4; odds ratio OR: 0.77, 95% confidence interval CI: 0.63–0.93) represents a consistent signal across nearly three decades. The multivariable analysis appropriately controls for several confounding variables. Particularly noteworthy is the consistency of baseline characteristics between quarters. PSA levels, age distribution, and comorbidity rates show no significant differences, strengthening the argument that observed variations reflect genuine biological differences rather than patient selection bias. The proposed vitamin D mechanism has compelling scientific support. Montréal’s dramatic seasonal sunshine variation, from 272 h in July to merely 80 h in December, creates ideal conditions for testing vitamin D-mediated effects. The 3-month lag between peak sunshine and reduced high-grade diagnoses aligns well with vitamin D’s biological half-life and potential effects on cellular differentiation. This seasonal hypothesis is consistent with prior work by Murphy et al.2 who found that serum vitamin D deficiency was independently associated with higher-grade prostate cancer at biopsy, particularly in African American men. The authors appropriately contextualize their findings within broader epidemiological evidence linking latitude, sunshine exposure, and prostate cancer outcomes, including the north–south gradient in prostate cancer mortality and protective effects of occupational sun exposure combined with favorable vitamin D receptor polymorphisms. Notably, Cooper et al.3 demonstrated that vitamin D3 supplementation in men on active surveillance may influence PSA dynamics, further underscoring the potential biologic relevance of individual vitamin D levels in early-stage prostate cancer. However, several significant limitations merit emphasis. The absence of individual vitamin D measurements represents the study’s most important weakness. Without serum 25-hydroxyvitamin D levels, the proposed mechanism remains entirely speculative. Moreover, studies like that by Murphy et al.2 emphasize that serum levels, not just inferred sunlight exposure, are essential to understand vitamin D’s relationship with Gleason upgrading and biopsy outcomes. Perhaps, most concerning is inadequate adjustment for healthcare utilization patterns. Physician vacation schedules or patient behavior might influence biopsy timing in ways that correlate with disease severity. While statistically significant, the clinical significance requires nuanced interpretation. The absolute difference between Q4 and Q1–Q3 (19.0% vs 22.9%) is modest, and the confidence interval approaches unity at its upper bound. The bundling of months into quarters obscures potentially informative granular patterns, with only January achieving borderline significance in individual month analysis, raising questions about the robustness of quarterly findings. The study’s most valuable contribution may be highlighting environmental influences on cancer biology. The integration of epidemiological observations with molecular biology, particularly circadian genes like period 1 (Per1) and their interaction with androgen receptor signaling, represents sophisticated thinking about cancer biology.4 However, clinical implications remain unclear. The modest effect size and numerous potential confounders preclude immediate practice changes. The findings should not influence biopsy timing decisions or vitamin D supplementation strategies beyond current evidence-based guidelines. The authors demonstrate appropriate scientific caution, acknowledging the correlational nature of their findings. This restraint should guide interpretation. The study generates important hypotheses rather than providing definitive answers about environmental influences on prostate cancer biology. COMPETING INTERESTS All authors declare no competing interests.
Islam et al. (Tue,) studied this question.