Fragmented sleep can increase cancer growth and aggression, according to a study published in the journal Cancer Research. Whilst fragmented sleep, a common feature of Obstructive Sleep Apnea, had previously been associated with an increase in cancer incidence and mortality, this is the first study to demonstrate a direct effect of poor sleep quality on tumour growth in a living animal.

Researchers from The University of Chicago and the University of Louisville fragmented the sleep of mice, waking them up every two minutes during sleep, for a week, before injecting them with cancerous cells. All mice developed tumours within twelve days of injection and their tumours were measured after four weeks. There was an increase in tumour size, weight and invasiveness in fragmented sleep mice compared to control animals.

Furthermore, sleep deprived mice had increased counts of tumour associated macrophages (TAMs), immune cells that respond differently to cancer depending on the chemical signals they receive. M1 TAMs promote an immune response and eliminate tumour cells, whilst M2 TAMs suppress an immune response and encourage tumour growth. Fragmented sleep induced a TAM polarity shift so that there was more M2 expression than M1 expression in tumours; a possible explanation for the observed increase in tumour growth. This shift in TAM expression was attributed to a molecule called ‘toll-like receptor 4’ (TLR4), because genetic deletion of this molecule abolished the increase in tumour size and aggressiveness seen in fragmented sleep mice. TLR4 knockout animals also had lower TAM counts.

This study demonstrates a clear relationship between sleep fragmentation and cancer growth, providing a possible mechanistic explanation via the body’s immune response. Future research in the field should look to determine if sleep disruption causes resistance to cancer therapies such as chemotherapy.

Read more at: http://ezproxy.ouls.ox.ac.uk:2739/content/early/2014/01/18/0008-5472.CAN-13-3014.full.pdf