Short read
Laukkanen and colleagues followed 2,173 Finnish men aged 42 to 61 with no history of cancer in a prospective cohort study, published in the European Journal of Cancer in 2019. Median follow-up was 24.3 years, during which 588 cancer cases occurred, 27.1 % of the cohort. Repeat assessments eleven years apart allowed the analysis to correct for changes in each man's sauna habits over time.
Measured against infrequent sauna use within the same cohort, sauna frequency showed no association with overall cancer risk. There was also no association with prostate or gastrointestinal cancer. In the age-adjusted analysis, a signal appeared for lung cancer; after full adjustment it was no longer significant.
The result is null in both directions: the data show neither a benefit nor a harm. The study includes men only and rests on a single cohort. The authors explicitly call for replication, particularly in women and in other age groups.
The null finding matters for two reasons. It addresses a real concern, the assumption that passive heat might raise cancer risk, and finds no association in these men. It also shows that the research group behind the positive cohort findings publishes results that show nothing. The study does not show that sauna use protects against cancer, and it does not rule out effects in groups that were not studied.