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Lessons from the Ohsaki Cohort: Sleep Duration and Cancer Risk
Jacob Schor ND, FABNO
Ground Hogs Day 2010
If there is a lesson to be learned from Groundhog’s Day, a kind of moral to the story, it is that it’s OK to go back to sleep. We are designed, or doomed, to spend a major portion of our lives asleep. That may seem like a waste of our time but we need the downtime to maintain our health. A pair of studies using data from the Ohsaki Cohort tells us that sleep is important for cancer prevention.
The Ohsaki Cohort refers to a large Japanese study, properly named The Ohsaki National Health Insurance Cohort Study. It was a population-based, prospective cohort study initiated in 1994 among 40,530 Japanese adults aged 40 to 79 years without history of stroke, coronary heart disease, or cancer at baseline. Participants were followed for up to 11 years (1995-2005) for all-cause mortality and for up to 7 years (1995-2001) for cause-specific mortality. Researchers have been analyzing the data collected ever since. For example Kuriyama’s study that tells us green tea consumption lowers cardiovascular disease, but not cancer, comes from this data.
Kakizaki and colleagues have mined this data looking for the effect sleep has on cancer risk. Their analysis yielded two papers published in 2008 in the British Journal of Cancer, one on prostate cancer and a second on breast cancer risk correlated with sleep duration.
Both studies reported similar results; inadequate sleep increases cancer risk.
The prostate study was published in July 2008. Three studies had already been published linking sleep duration with breast cancer risk. The theory put forward to explain this effect is that it is due to melatonin. This is the hormone that is secreted from the pineal gland and that plays a role in sleep duration. Melatonin influences the synthesis and secretion of sex hormones by promoting the release of gonadotropin-releasing hormone.
This theory that low melatonin increases cancer risk is supported by several observational studies that tell us that night work, shift work or visual impairment increase risk of sex hormone-related cancers such as prostate or breast. There have even been studies on the increased risk caused by outdoor lighting at night. These are the first papers to look at sleep duration and cancer risk.
Of the 22,320 Ohsaki men , 127 developed prostate cancer. The longer the men slept at night the lower their risk. [“… the multivariate hazard ratio of men who slept >or=9 h per day compared with those who slept less was 0.48 (95% confidence interval: 0.29-0.79, P for trend=0.02).”] The men who slept more than 9 hours a night had less than half the risk of getting prostate cancer as those who slept less. Who in the world gets to or can sleep nine hours a night? Though statistically significant data, one has to question the clinical relevance, that is the likelihood of getting a substantial number of men to sleep this much is so low as to be unfeasible. In women though the effect was more pronounced and discernable with less time spent asleep.
In this study 23,995 women were followed, 143 developed breast cancer. The women were divided up by whether they slept 7 hours per day or 6 hours or less. The later group, those who slept 6 hours or less per day had a, “…multivariate hazard ratio of those who slept </=6 h per day was 1.62 (95% confidence interval: 1.05-2.50; P for trend=0.03).”
Translated that means they were about one and a half times more likely to get breast cancer than those who slept 7 hours. Once again, as in the prostate cancer study, the longer the better. Women who reported sleeping 9 hours or more a night had a lower risk, a hazard ratio of 0.72 (95% CI: 0.36–1.43) (P for trend=0.03) compared to the 7 hour sleepers. Thus they were about a 25% less likely to get breast cancer.
Perhaps it is time to rewrite the groundhog story. Whether he sees his shadow or not, he should go back to sleep.
Perhaps the same could be said for the ‘early bird gets the worm’ and that ‘healthy, wealthy and wise’ saying as well. As a footnote, that ‘early to bed, early to rise, makes a man healthy, wealthy and wise’ proverb is usually attributed to Benjamin Franklin but in fact was first published in 1639 in the book Parœmiologia Anglo-Latina. Back in Franklin’s day, people averaged a good ten hours of sleep each night. Getting up a little earlier may not have hurt and the idea that getting a headstart on your peers might have had value. Encouraging people to sleep less is no longer a good idea. It is bad medicine. The lesson for this Groundhog’s Day is whether we see our shadow or not, maybe it’s time to go back to bed for a little more sleep.
Other Melatonin Newsletters:
Melatonin and Breast Cancer Review: http://denvernaturopathic.com/news/MelatoninandBreastCancer.html
Light at Night and Breast Cancer Risk: http://denvernaturopathic.com/lightatnight.htm
Blue Light and Melatonin: http://denvernaturopathic.com/bluelightandmelatonin.htm
Kuriyama S, Shimazu T, Ohmori K, Kikuchi N, Nakaya N, Nishino Y, Tsubono Y, Tsuji I. Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study. JAMA. 2006 Sep 13;296(10):1255-65.
Free Full Text: http://jama.ama-assn.org/cgi/content/full/296/10/1255
JAMA. 2006 Sep 13;296(10):1255-65.
Division of Epidemiology, Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan. firstname.lastname@example.org
CONTEXT: Green tea polyphenols have been extensively studied as cardiovascular disease and cancer chemopreventive agents in vitro and in animal studies. However, the effects of green tea consumption in humans remain unclear. OBJECTIVE: To investigate the associations between green tea consumption and all-cause and cause-specific mortality. DESIGN, SETTING, AND PARTICIPANTS: The Ohsaki National Health Insurance Cohort Study, a population-based, prospective cohort study initiated in 1994 among 40,530 Japanese adults aged 40 to 79 years without history of stroke, coronary heart disease, or cancer at baseline. Participants were followed up for up to 11 years (1995-2005) for all-cause mortality and for up to 7 years (1995-2001) for cause-specific mortality. MAIN OUTCOME MEASURES: Mortality due to cardiovascular disease, cancer, and all causes. RESULTS: Over 11 years of follow-up (follow-up rate, 86.1%), 4209 participants died, and over 7 years of follow-up (follow-up rate, 89.6%), 892 participants died of cardiovascular disease and 1134 participants died of cancer. Green tea consumption was inversely associated with mortality due to all causes and due to cardiovascular disease. The inverse association with all-cause mortality was stronger in women (P = .03 for interaction with sex). In men, the multivariate hazard ratios of mortality due to all causes associated with different green tea consumption frequencies were 1.00 (reference) for less than 1 cup/d, 0.93 (95% confidence interval [CI], 0.83-1.05) for 1 to 2 cups/d, 0.95 (95% CI, 0.85-1.06) for 3 to 4 cups/d, and 0.88 (95% CI, 0.79-0.98) for 5 or more cups/d, respectively (P = .03 for trend). The corresponding data for women were 1.00, 0.98 (95% CI, 0.84-1.15), 0.82 (95% CI, 0.70-0.95), and 0.77 (95% CI, 0.67-0.89), respectively (P<.001 for trend). The inverse association with cardiovascular disease mortality was stronger than that with all-cause mortality. This inverse association was also stronger in women (P = .08 for interaction with sex). In women, the multivariate hazard ratios of cardiovascular disease mortality across increasing green tea consumption categories were 1.00, 0.84 (95% CI, 0.63-1.12), 0.69 (95% CI, 0.52-0.93), and 0.69 (95% CI, 0.53-0.90), respectively (P = .004 for trend). Among the types of cardiovascular disease mortality, the strongest inverse association was observed for stroke mortality. In contrast, the hazard ratios of cancer mortality were not significantly different from 1.00 in all green tea categories compared with the lowest-consumption category. CONCLUSION: Green tea consumption is associated with reduced mortality due to all causes and due to cardiovascular disease but not with reduced mortality due to cancer.
PMID: 16968850 [PubMed - indexed for MEDLINE]
Kakizaki M, Inoue K, Kuriyama S, Sone T, Matsuda-Ohmori K, Nakaya N, Fukudo S, Tsuji I; Ohsaki Cohort Study. Sleep duration and the risk of prostate cancer: the Ohsaki Cohort Study. Br J Cancer. 2008 Jul 8;99(1):176-8. Epub 2008 Jun 10.
Free Full Text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2453016/?tool=pubmed
Division of Epidemiology, Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan. email@example.com
In a prospective study of prostate cancer incidence (127 cases), among 22 320 Japanese men, sleep duration was associated with lower risk; the multivariate hazard ratio of men who slept >or=9 h per day compared with those who slept less was 0.48 (95% confidence interval: 0.29-0.79, P for trend=0.02).
Kakizaki M, Kuriyama S, Sone T, Ohmori-Matsuda K, Hozawa A, Nakaya N, Fukudo S, Tsuji I. Sleep duration and the risk of breast cancer: the Ohsaki Cohort Study. Br J Cancer. 2008 Nov 4;99(9):1502-5.
Free Full Text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2579702/?tool=pubmed
Division of Epidemiology, Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan.
In a prospective study of 23 995 Japanese women, short sleep duration was associated with higher risk of breast cancer (143 cases), compared with women who slept 7 h per day, the multivariate hazard ratio of those who slept </=6 h per day was 1.62 (95% confidence interval: 1.05-2.50; P for trend=0.03).
PMID: 18813313 [PubMed - indexed for MEDLINE]