(NBCNEWS) — Men who have a hard time falling asleep and staying asleep may be at an increased risk of prostate cancer, according to a new study from Icelandic and American researchers.

The new study published Tuesday in the journal Cancer Epidemiology, Biomarkers and Prevention showed an association between disturbed sleep and not only an increased incidence of prostate cancer but also the severity of prostate cancer.

An association does not mean that disturbed sleep causes the cancer, only that the two appear linked, though the paper’s authors do speculate that one mechanism may involve the brain chemical melatonin. Some research shows melatonin production at night can help suppress cellular processes involved in cancer growth. Light and disturbed sleep inhibits melatonin production.

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