Surgery and Orthopedics Poster Session

Reduced Cancer incidence in the blind. ? Melatonin influence

Myles Clough

While looking over a PubMed search on Cancer incidence (see comments on Dr Gonzalez-Navarro's paper) I came across this one which I find absolutely fascinating.
Epidemiology 1998 Sep;9(5):490-4
Reduced cancer incidence among the blind.
Feychting M, Osterlund B, Ahlbom A
Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.

Melatonin is a hormone primarily produced by the pineal gland at night and is suppressed by exposure to light. Experimental
studies have indicated that melatonin may protect against cancer development. In the majority of totally blind people, melatonin
is never suppressed by light exposure. The aim of this study was to test the hypothesis that blind people have a decreased
cancer incidence, and that this effect is more pronounced in the totally blind than in the severely visually impaired. We identified
a cohort of 1,567 totally blind and 13,292 severely visually impaired subjects and obtained information about cancer incidence
from the Swedish Cancer Registry. We calculated standardized incidence ratios (SIRs) based on the number of person-years
and incidence rates specific for national age, sex, and calendar year. Totally blind people had a lower incidence of all cancers
combined [SIR = 0.69; 95% confidence interval (CI) = 0.59-0.82]. The risk reduction was observed in both men and women
and was equally pronounced in hormone-dependent tumors as in other types of cancer. In the severely visually impaired, SIR
was 0.95 (95% CI = 0.91-1.00). The findings support the hypothesis that blind people have a lower cancer incidence,
although other explanations than the higher melatonin exposure must also be considered.

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