Associations between hospitalized infections in the first 24 months of life and risk of cancer in early-mid adulthood.

Background: It is increasingly recognized that early life factors play a role in the rising prevalence of cancer in young adult life. Acute childhood infections may protect against development of cancer, but evidence is limited. We investigated whether infection-related hospital contacts during the first 24 months of life were associated with the risk of cancer in early-mid adult life in a large population-based Danish cohort.

Methods: We included 68,538 individuals (33,569; 49.0 % women) born 1977-1996 from the Copenhagen School Health Records Register. Using individual-level linkage to national registries, we obtained information on infection-related hospital contacts between birth and 24 months and early-onset cancer (diagnosed 15-45 years). Hazard ratios (HR) and 95 % confidence intervals (CI) were estimated using Cox regressions adjusted for maternal education.

Results: From birth to 24 months of life, 14,718 individuals (21.5 %) had at least one infection-related hospital contact. During follow-up, 788 individuals were diagnosed with cancer. Compared to individuals who did not have an infection-related hospital contact, those who had a least one had a lower risk of early-mid adulthood cancer (HR=0.82, 95 % CI: 0.68-0.98). We found limited evidence of a dose-response inverse effect of infection-related hospital contacts on cancer risk.

Conclusion: Infection-related hospital contacts during the first 24 months of life was associated with a reduced risk of cancer in early-mid adult life. Replication in other populations is warranted and mechanistic studies are needed to understand the biological mechanisms underlying these epidemiological observations.