A third study showed patients with more severe obstructive sleep apnoea, as measured by AHI and markers of nocturnal oxygen deprivation, were more likely to develop blood clots (venous thromboembolism) that can trigger heart attacks or stroke.

UPPSALA, Sweden — Snorers could be at an increased risk of cancer, cardiovascular disease and dementia, according to new research. Scientists in Sweden say obstructive sleep apnoea, in which snoring is the main symptom, cuts off oxygen supply — fuelling tumours, blood clots and loss of brain cells.

Obstructive sleep apnoea (OSA) affects about 30 million Americans — though only 6 million are diagnosed cases, according to the American Medical Association. The condition causes the walls of the throat relax and narrow, interrupting normal breathing several times a night. Overweight individuals are particularly prone to OSA. Preventative measures include weight loss or wearing a mask in bed which blows air into the back of the throat.

The findings, presented at the European Respiratory Society (ERS) meeting in Barcelona, could lead to screening programs. They are based on three studies across Europe.

“It’s known already patients with obstructive sleep apnoea have an increased risk of cancer, but it has not been clear whether or not this is due to the OSA itself or to related risk factors for cancer, such as obesity, cardiometabolic disease and lifestyle factors,” says Dr. Andreas Palm, a researcher and senior consultant at Uppsala University, in a statement. “Our findings show that oxygen deprivation due to OSA is independently associated with cancer.”

Study authors analysed data on 62,811 Swedes five years before they started being treated for obstructive sleep apnoea with a CPAP (continuous positive airway pressure) mask. They combined it with information from the Swedish National Cancer Registry, taking into account body size, other health problems and socio-economic status. It enabled them to match 2,093 patients with OSA and a diagnosis of cancer up to five years before OSA diagnosis with a control group of 2,093 patients with OSA but no cancer.

Severity was measured with the apnoea hypopnea index (AHI) — which counts breathing disturbances during sleep — or the oxygen desaturation index (ODI), which measures how many times an hour blood levels fall by at least three percent for ten seconds or longer.

“We found patients with cancer had slightly more severe OSA, as measured by an apnoea hypopnea index average of 32 versus 30, and an oxygen desaturation index of 28 versus 26,” says Palm. “In further analysis of subgroups, ODI was higher in patients with lung cancer (38 versus 27) prostate cancer (28 versus 24) and malignant melanoma (32 versus 25).

“The findings in this study highlight the need to consider untreated sleep apnoea as a risk factor for cancer and for doctors to be aware of the possibility of cancer when treating patients with OSA,” Palm continues. “However, extending screening for cancer to all OSA patients is not justified or recommended by our study results.”

The researchers plan to increase the number of patients and to follow the patients over time to study the potential influences of CPAP treatment on cancer incidence and survival.

“The association between OSA and cancer is less well established than the link with diseases of the heart and blood vessels, insulin resistance, diabetes and fatty liver disease,” adds Palm. “Therefore, more research is needed, and we hope our study will encourage other researchers to research this important topic.”

Obstructive sleep apnoea's impact on the brain
A second study identified a link between OSA and greater decline in brainpower over a period of five years. It was based on sleep tests undertaken by 358 over 65s in Switzerland. Global cognitive and executive function, verbal memory, language and visual perception of spatial relationships were also assessed.

“We found that OSA and, in particular, low oxygen levels during sleep due to OSA, was associated with a greater decline in global cognitive function, processing speed, executive function and verbal memory,” says Dr. Nicola Marchi of Lausanne University. “We also found that people aged 74 and older and men were at higher risk of cognitive decline related to sleep apnoea in some specific cognitive tests.”

For example the Stroop test, which measures processing speed and executive function, showed a steeper decline in people aged 74 and older compared to younger participants. Verbal fluency showed a steeper decline in men, but not in women.

“This study demonstrates the severity of sleep apnoea and night-time oxygen deprivation contribute to cognitive decline in old age,” says Dr. Marchi. “It also shows that sleep apnoea is related to a decline in specific cognitive functions, such as processing speed, executive function and verbal memory, but not to a decline in all cognitive functions; for instance, language and visuospatial function were not affected.

“People with OSA and doctors should be aware that OSA may play a role in cognitive decline. However, to date, OSA treatment with continuous positive airway pressure (CPAP) has not been clearly demonstrated to prevent cognitive decline,” says Marchi. “Our study suggests that probably not all OSA patients have the same risk of cognitive decline; there is probably a subgroup of patients, particularly those with greater nocturnal oxygen deprivation but also older patients and men, who could be at greater risk of OSA-related cognitive decline.”

The researchers plan to analyse data on the impact of OSA after ten years to find out more about who is at most risk of cognitive decline. Dr. Marchi suggests performing a randomized controlled trial with these patients in order to investigate the effect of CPAP on cognition should be the next step after that.

Higher risk of blood clots
A third study showed patients with more severe obstructive sleep apnoea, as measured by AHI and markers of nocturnal oxygen deprivation, were more likely to develop blood clots (venous thromboembolism) that can trigger heart attacks or stroke.

“This is the first study to investigate the association between obstructive sleep apnoea and the incidence of unprovoked venous thromboembolisms,” explains Wojciech Trzepizur, from Angers University Hospital in France. “We found that those who spent more than six percent of their night-time with levels of oxygen in their blood below 90 percent of normal had an almost two-fold risk of developing VTEs as compared to patients without oxygen deprivation. Further studies are required to see whether adequate treatment for OSA, for instance with CPAP treatment, might reduce the risk of VTEs in patients with marked nocturnal oxygen deprivation.”

The results were based on 7,355 patients followed for more than six years of whom 104 developed VTEs.

Professor Winfried Randerath, of the Bethanien Hospital at the University of Cologne, Germany, is head of the ERS specialist group on sleep disordered breathing and was not involved in the three studies. “These three studies show worrying associations between obstructive sleep apnoea and important diseases that affect survival and quality of life,” he says. “The data support the relevance of sleep apnoea on cancer, venous thromboembolisms and mental health. While they cannot prove that OSA causes any of these health problems, people should be made aware of these links and should try to make lifestyle changes in order to reduce their risk of OSA, for instance, by maintaining a healthy weight.

“However, if OSA is suspected, definite diagnosis and treatment should be initiated,” he emphasizes. “We look forward to further research that may help to clarify whether OSA may be causing some of the health problems seen in these studies.”

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