Why cancer prognosis might shift with the changing seasons
In short: We often associate seasonal changes with the spread of the flu, but researchers have observed striking patterns in cancer outcomes. In certain regions, the time of year a patient is diagnosed may significantly influence their prognosis, potentially linked to the sun's influence on our biology.
While many assume that seasonal patterns in disease are driven by infectious agents, public health experts have noted similar behaviors in non-infectious diseases like breast cancer. However, the data regarding cancer incidence and death rates is complex. In many high-latitude countries, overall death rates peak during the winter. Yet, when looking specifically at internal cancers, researchers have found no consistent, significant seasonal variation in either the rate of diagnosis or the rate of death.
The real variation may lie in prognosis—the likely course of the disease—rather than how often it appears. In a study conducted in Norway, researchers discovered that patients diagnosed in the summer and autumn experienced a better prognosis than those diagnosed in the winter and spring. This finding is particularly notable because the study found no corresponding shifts in diagnosis or death rates that could otherwise explain these improved outcomes.
The leading hypothesis for this seasonal gap is the population's vitamin D status. In Norway, vitamin D levels are significantly higher during the summer and autumn due to increased photosynthesis in the skin. Because vitamin D levels fluctuate with the seasons, the researchers suggest that the better prognosis in warmer months aligns with the seasons of peak vitamin D availability. While some have previously attributed seasonal variations to circannual hormone changes, the data remains inconsistent, leaving the link between solar radiation and vitamin D levels as a primary area of investigation.
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Sources
- Summary by Intellect · source: Breast Cancer gets Worse in the Spring and Fall. But...Why?
- Also: Seasonal variations of cancer incidence and prognosis
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