Does incidence of breast cancer and prostate cancer decrease with increasing degree of visual impairment.
Level 3 - non-randomized controlled study
Non-randomized registry-based cohort follow-up study
PubMed 16596312 · doi:10.1007/s10552-005-9005-6
What was done
Researchers conducted a cohort follow-up study linking 17,557 individuals with visual impairment from the Finnish Register of Visual Impairment to the Finnish Cancer Registry for the years 1983–2003. They evaluated whether the degree of visual impairment was associated with the incidence of breast cancer, prostate cancer, and other cancers compared with the general Finnish population.
What was found
Breast cancer risk in females decreased with increasing degree of visual impairment, and a similar though less consistent trend was observed for prostate cancer in males. In contrast, the incidence of remaining cancers among nearly to totally blind individuals was significantly higher than in the average Finnish population. The abstract provides no specific numerical values, rate ratios, or confidence intervals.
Why it matters
This study provides epidemiological support for a specific link between visible light, melatonin signaling, and hormone-related cancers like breast cancer. It also argues against the broader theory that lack of light exposure confers a generalized systemic protection against all cancers.
Limits
The abstract reports only directional trends and significance without providing exact numbers, relative risks, or confidence intervals. As an observational registry linkage, it lacks control for potential confounders such as reproductive factors, lifestyle, screening behavior, or the underlying medical causes of blindness.
Cited by
- contradicts Blind individuals produce more melatonin and have half the cancer incidence compared to sighted individuals.