Sleep apnea linked to cancer in a study

15/4/2014

Moderate-to-severe obstructive sleep apnea was linked with 2.5 times higher likelihood of cancer, after adjustment for obesity and many other factors.

This was the outcome of research by Nathaniel Marshall, PhD, of the University of Sydney Nursing School in Australia, and colleagues in the context of a longitudinal population-based study of obstructive sleep apnea (OSA).

Cancer mortality was 3.4 times more common in those with sleep apnea than with no sleep apnea during 20 years of follow-up, they reported in the Journal of Clinical Sleep Medicine.

Studies associating cancer with sleep apnea

Those findings were in line with two other observational studies, one from Wisconsin showing a 2.0-fold higher risk of dying from cancer with moderate OSA and 4.8-fold risk with severe OSA, and one from Spain showing elevated cancer incidence as well.

All three analyses were spurred by mouse model findings suggesting that hypoxia spurred more rapid tumor growth, Richard Kim, MD, and Vishesh K. Kapur, MD, MPH, both of the University of Washington in Seattle, noted in an accompanying editorial.

While the Australian study used a nonstandard, out-of-center sleep-testing device and had a relatively small sample size, it adds another cohort in support of causality, they said.

Kim and Kapur wrote: "In the Bradford Hill criteria for assessing causality, an important factor is whether the association has 'been repeatedly observed by different persons, in different places, circumstances and times. Additional long-term longitudinal studies which include objective assessment of OSA, more extensive ascertainment of important confounders, and detailed cancer outcomes are needed. Indeed, a variety of study types, including mechanistic and interventional studies, would help more fully ascertain whether a causal relationship between OSA and cancer exists."

Study details

Marshall's analysis included 397 men and women who had a baseline four-channel at-home sleep test as part of the larger Busselton Health Study of residents of that rural Western Australia town. It showed other expected links to health risks of moderate-to-severe sleep apnea, including overall mortality & stroke. Whereas links to cardiovascular risks have been well established in other studies, those were not significant in the Busselton study. "Mortality and morbidity in OSA seem to be driven by a combination of cancer and cardiovascular disease (particularly stroke)," the researchers wrote. "This overall elevation in mortality from a range of causes may be making it difficult to confirm statistically the cardiovascular component here, specifically. This may also be partly due to the Busselton having lower cardiovascular disease rates than surrounding areas and Western Australia in general."

Mild sleep apnea (defined by five to 15 apnea events per hour) was associated with a significant halving in mortality, but only in the fully adjusted model and without any other impact on outcomes.

"We tentatively suggest this might mean that mild sleep apnea protects people against the effects of their other clustered cardiometabolic risk factors," perhaps through ischemic preconditioning, Marshall's group suggested.

They cautioned that their study was underpowered, "particularly with only 18 people in the highest exposure category."

 

Source: MedPage Today: http://www.medpagetoday.com/PrimaryCare/SleepDisorders/45272

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