Sleep apnoea linked to cancer, blood clots, lower mental processing

People who suffer from obstructive sleep apnoea (OSA) are at an increased risk of cancer, according to a large study presented at the recent European Respiratory Society (ERS) International Congress in Barcelona.

A second study showed that OSA was also linked to a decline in processing powers in the elderly; in particular, those aged 74 years or more and men showed a steeper decline in certain cognitive tests. A third study found that patients with more severe OSA were at greater risk of developing blood clots in their veins — a potentially life-threatening condition.

OSA is a common sleep disorder whereby people experience partial or complete obstruction of their airways during sleep and stop breathing several times a night. This can manifest as loud snoring, gasping, choking and daytime sleepiness. It is believed to affect at least 7–13% of the population; people who are overweight or obese, have diabetes, or who smoke or consume large amounts of alcohol are most at risk of OSA.

The first study was presented by Dr Andreas Palm, a researcher and senior consultant at Uppsala University. He said: “It is known already that 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. Our findings show that oxygen deprivation due to OSA is independently associated with cancer.”

Palm and colleagues looked at data from 62,811 patients five years prior to the start of treatment for OSA in Sweden. Between July 2010 and March 2018, patients were treated with continuous positive airway pressure (CPAP), which provides a positive pressure of air through a mask to keep the airways open during sleep. The researchers linked these data with data from the Swedish National Cancer Registry and socio-economic data from Statistics Sweden.

The researchers took account of factors that could affect the results such as body size, other health problems and socio-economic status. They matched 2093 patients with OSA and a diagnosis of cancer up to five years before OSA diagnosis with a control group of 2093 patients with OSA but no cancer. They measured the severity of OSA with the apnoea hypopnea index (AHI), which measures the number of breathing disturbances during sleep, or the oxygen desaturation index (ODI), which measures how many times an hour levels of oxygen in the blood fall by at least 3% for 10 seconds or longer.

“We found that 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,” he said. “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 said. In the future, the colleagues 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 researchers acknowledged that the study cannot show that OSA causes cancer — only that it is associated with it — and that important lifestyle factors such as physical activity and food preferences were not captured on an individual basis in the study. The study authors hope their work will encourage others to research this important topic.

In a second presentation, Professor Raphaël Heinzer, Director of the Centre for Investigation and Research on Sleep (CIRS) at the University of Lausanne, said a study conducted with his colleague Dr Nicola Marchi showed that OSA was linked to a greater decline in mental processing powers over a period of five years.

Heinzer, Marchi and colleagues studied people aged 65 years and over from the general population of Lausanne who were recruited to the CoLaus/PsyCoLaus and HypnoLaus studies between 2003 and 2008, and who were followed up every five years. A total of 358 participants took a sleep test to examine the presence and severity of OSA when they joined the studies. During the first follow-up between 2009 and 2013, their mental processing abilities were also tested and another cognitive assessment took place during the second follow-up five years later.

The cognitive tests assessed global cognitive function (knowledge and reasoning skills), processing speed (time taken to understand and react to information), executive function (ability to organise thoughts and activities, prioritise tasks and make decisions), verbal memory, language and visual perception of spatial relationships between objects (visuospatial function).

“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,” Marchi said. “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, and the verbal fluency test showed a steeper decline in men only but not in women.

“This study demonstrates that the severity of sleep apnoea and night-time oxygen deprivation contribute to cognitive decline in old age,” Marchi said. “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. 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 10 years to find out more about who is at most risk of cognitive decline related to OSA. Marchi suggests that performing a randomised controlled trial with these patients in order to investigate the effect of CPAP on cognition should be the next step after that.

The third study, presented by Professor Wojciech Trzepizur from Angers University Hospital, showed that patients with more severe OSA, as measured by the Apnoea–Hypopnea Index (AHI) and markers of nocturnal oxygen deprivation, were more likely to develop venous thromboembolism (VTE). Out of 7355 patients followed over more than six years, 104 developed VTEs.

“This is the first study to investigate the association between obstructive sleep apnoea and the incidence of unprovoked venous thromboembolisms,” Trzepizur said. “We found that those who spent more than 6% of their night-time with levels of oxygen in their blood below 90% 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.”

Image credit: iStock.com/cherrybeans

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