New UK research suggests that people who regularly sleep too little or too much are more likely to have pulmonary fibrosis, compared to those who sleep the recommended seven hours a night.
The study, by researchers at the University of Manchester, looked at 500,074 participants taking part in the long-term UK Biobank study, which includes genomic data on more than half a million UK residents.
After finding that altering the internal body clock of mice could make the animals more likely to develop pulmonary fibrosis, the researchers wanted to see if the internal body clock, also known as circadian rhythm, could be linked to the disease in humans.
Pulmonary fibrosis is an incurable lung disease which occurs when lung tissue becomes damaged and scarred. The thicker, stiffer tissue makes it more difficult for the lungs to work properly, and as the disease progresses, sufferers become increasingly short of breath. It can be caused by a variety of factors, and kills about 5,000 people a year in the UK, the same number as leukemia.
The findings of this recent study, published in Proceedings of the National Academy of Sciences, showed that after taking into account known risk factors for pulmonary fibrosis such as body mass index, smoking, sex and age, participants who reported regularly sleeping four hours or less in a day had twice the chance of having the disease, while those sleeping 11 hours or longer in a day tripled their chance, compared to those sleeping seven hours per day.
Working late shifts or having an evening chronotype (being a "night owl" and having a preference for staying up late rather than getting up early) were also associated with the disease, but to a lesser extent.
The researchers said that the link between sleep duration and pulmonary fibrosis is similar in strength to other known risk factors for the disease. They attribute the association to the circadian clock, which regulates nearly every cell in the human body and is the driving force between the 24-hour cycles in many biological processes such as sleeping, hormone secretion and metabolism. Their previous work suggests that the lung is a highly circadian organ, and its responses to its environment are regulated by circadian rhythms. The team also added that in the lungs these rhythms mainly affect processes in the normal lung tissue in the main airways. However, they found that in people with pulmonary fibrosis, the oscillations of this 'clock' also affect the fibrotic tissue found in the small air spaces, called alveoli. Scarring and thickening of the tissue around and between the alveoli is what causes pulmonary fibrosis, with the team adding that circadian oscillations can alter wound-healing.
Dr. John Blaikley, who led the project said, "Pulmonary fibrosis is a devastating condition which is incurable at present. Therefore, the discovery that the body clock is potentially a key player potentially opens new ways to treat or prevent the condition. More work will need to be done around studying the association between pulmonary fibrosis and sleep duration to establish both causation and reproducibility. If these results are confirmed, then sleeping for the optimal time may reduce the impact of this devastating disease."