Protective role of melatonin in breast cancer: what we can learn from women with blindness.
Level 5 - mechanism / opinion, no new human data
Narrative review of observational and preclinical studies
PubMed 34837156 · doi:10.1007/s10552-021-01502-5
What was done
The authors reviewed published literature across four domains: breast cancer risk in blind women (7 studies), the association between circulating melatonin levels and breast cancer incidence in the general population (5 meta-analyses and 12 prospective cohort studies), clinical therapeutic applications of melatonin, and preclinical in vitro and animal mechanistic studies.
What was found
Seven studies in totally blind women reported breast cancer incidence reductions of up to 57%, though none measured circulating melatonin levels. In general-population cohorts and meta-analyses, melatonin levels showed no association with breast cancer risk in premenopausal women, whereas most studies found significantly decreased risk in postmenopausal women with the highest melatonin levels. Therapeutic use alongside chemotherapy, radiotherapy, or endocrine therapy was poorly documented, and antiestrogenic, antioxidant, oncostatic, and immunomodulatory mechanisms were observed only in preclinical models.
Why it matters
The review synthesizes epidemiological clues regarding circadian biology and breast cancer, cautioning that despite suggestive observational patterns in postmenopausal women, clinical preventive and therapeutic utility remains unconfirmed.
Limits
As a narrative review, it lacks systematic search methodology and pooled quantitative effect estimates. Included blindness studies frequently lacked adjustment for confounders and omitted direct melatonin profiling. Human clinical trial evidence for melatonin as an adjuvant therapy remains sparse.
Cited by
- partial Blind individuals produce more melatonin and have half the cancer incidence compared to sighted individuals.