bad night's sleep may mean more than feeling like an extra on The Walking Dead the next morning. According to new research presented at the European Association of Urology (EAU) Congress in Munich, it could mean cancer.

Previous studies have linked sleep apnea, a condition that affects an estimated 18 million Americans, to an increased risk of cancer death — although there is some conflicting evidence on this. One of the side effects of sleep apnea is hypoxia, a condition in which the body or organ is deprived of adequate oxygen. Now, a new animal study led by Dr. Antoni Vilaseca, of the Hospital Clinic of Barcelona in Spain, suggests this particular side effect may underlie the link between the sleep disorder and worse cancer outcomes.

Researchers used 24 mice with kidney tumors for their study — 12 were in an experimental group and 12 served as a control. After they subjected the experimental mice to varying oxygen levels to mimic intermittent hypoxia, researchers found they had an increased amount of vascular progenitor and endothelial cells within the kidney tumors. These cells play a role in the development and regeneration of blood vessels, which ultimately transport oxygen and nutrients to different tissues and organs. These mice also experienced an increase in a protein that is highly expressed in many tumors, called vascular endothelial growth factor (VEGF). 

Basically, hypoxia could increase the tumor's access to nutrients, in turn helping it to grow.

"Patients suffering from obstructive sleep apnea usually suffer from intermittent hypoxia at night," Vilaseca said in a statement. "This work shows that intermittent hypoxia has the potential to promote the formation of blood vessels within tumors, meaning that the tumors have access to more nutrients."

That said, other factors, such as tumor growth, were not affected.

"This is of course an early animal study, so we need to be cautious in applying this to humans," Vilaseca explained. "Nevertheless, this work indicates a plausible mechanism for just why conditions which restrict oxygen flow to tissues, like sleep apnea, may promote cancers."

Dr. Arnulf Stenzl, chair of the EAU Congress Committee, added the present findings demonstrate why not smoking and other healthy lifestyle changes are associated with reduced cancer risk — it could be more oxygen leads to better outcomes in kidney cancer, as well as other tumor types, Stenzl said.

Past research has also linked sleep apnea to an increased risk of high blood pressure, stroke and depression. However, it isn't the only disorder linked to adverse health outcomes. Poor or insufficient sleep, which affect an estimated 50 to 70 million Americans, is associated with greater risk for type 2 diabetes, Alzheimer’s and weight gain.

Not sure how to improve your sleep? Check out these nine science-backed tips.

Source: European Association of Urology Congress. 2016.