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More sleep reduces breast cancer risk
A study reported in the October 15 2005 issue of the journal Cancer Research is the first to reveal an association between greater sleep length and a reduced incidence of breast cancer.
Researchers in Finland examined data obtained in the Finnish Twin Cohort, which includes over 32,000 twins born before 1958. The current study involved 12,222 female participants who replied to one or more questions concerning sleep duration, quality and sufficiency in 1975 or 1981. Data on breast cancer diagnoses from 1976 to 1996 was obtained from the Finnish Cancer Registry.
During the 30 year period 242 cases of breast cancer were diagnosed. Although women who were classified as having short sleep duration of six hours or less had a modestly lower breast cancer risk than that experienced by those with an average sleep duration of 7 to 8 hours, women who were categorized as long sleepers experienced a 31 percent reduction in the risk of breast cancer compared to average sleepers.
In a separate analysis of 7,396 so-called stable sleepers, whose answers on sleep duration in 1981 were unchanged from those of 1975, short sleepers experienced a 10 percent greater risk of breast cancer than average sleepers, while long sleepers experienced a significant 72 percent reduction compared to average sleepers. The separate analysis was conducted in recognition of the impact of long-term factors on breast cancer risk.
The authors hypothesized that sleep patterns may influence breast cancer risk via changes in melatonin and other hormonal rhythms, and acknowledged that the greater prevalence of artificial lighting at night could be a contributor to the current increase in breast cancer incidence via its ability to reduce melatonin levels. In their discussion of the current study’s findings, they cite studies that support this hypothesis, such as several that have found an association between night shift work and breast cancer risk, or those that have determined a reduction in risk among blind women. They conclude, “The suggestion of lower breast cancer risk in long sleepers in the Finnish Twin Cohort adds to the body of evidence for a possible anticarcinogenic effect of melatonin.”