Though the study was done with animals, study director David Gozal, chairman of pediatrics at the University of Chicago Comer Children’s Hospital aimed to present that fragmented sleep has an affect on tumor growth and invasiveness. He says, “It’s not the tumor, it’s the immune system. Fragmented sleep changes how the immune system deals with cancer in ways that make the disease more aggressive.” Dr Gozal read a couple of recent studies linking sleep apnea and cancer mortality and he and some colleagues from the University of Chicago and the University of Louisville planned some experiments to measure the affects of fragmented sleep on cancer using mice housed in small groups.
To start the experiment, the mice were housed in two groups. Half of the mice, who sleep in the day, were woken up every two minutes while a quiet motorized brush ran across their cage and then they would go back to sleep. The other half of the mice were allowed to sleep peacefully.
When one week had passed, the mice were all injected with cells that would grow into tumors. Within 9-12 days tumors were present and after 4 weeks, the tumors were evaluated.
“In that setting, tumors are usually encased by a capsule of surrounding tissue, like a scar,” Gozal said. “They form little spheres, with nice demarcation between cancerous and normal tissue. But in the fragmented-sleep mice, the tumors were much more invasive. They pushed through the capsule. They went into the muscle, into the bone. It was a mess.”
The authors, who include Fahed Hakim, Yang Wang, Shelley Zhang, Jiamao Zheng, Alba Carreras, Abdelnaby Khlayfa and Isaac Almendros from the University of Chicago; and Esma S. Yolcu and Haval Shirwan from the University of Louisville found that the tumors in the mice with the fragmented sleep were twice the size of the others. In addition, they added to the experiment by moving the tumors to the thigh muscle of the mice in an effort to contain their growth. They found that the tumors were much more aggressive and invaded surrounding tissues in mice with disrupted sleep.
“This study offers biological plausibility to the epidemiological associations between perturbed sleep and cancer outcomes,” Gozal said. “The take home message is to take care of your sleep quality and quantity like you take care of your bank account. Considering the high prevalence of both sleep disorders and cancer in middle age or older populations,” the authors wrote, “there are far-reaching implications.”