Why does asthma get worse at night?

In 1698 the British Dr. John Floer wrote a treatise on asthma, the first major work focused on the disease. Not everyone grew old well. He warned that those who are sad or angry are more likely to have seizures, as sadness will stop the Humor Movement. He also recommended several treatments, including regular, mild vomiting.

In an asthma attack, the airways in a person’s lungs begin to close, making it difficult for them to breathe and causing chest tightness, coughing and wheezing. But Floer’s piece noted another important symptom: his own asthma was almost always more severe at night, sometimes waking him up at 1 or 2 in the morning. Hundreds of years later, scientists found evidence to support it: A 2005 study found that nearly 75 percent of people with asthma had more severe nocturnal attacks. A well-known study of mortality in London hospitals in the 1970s showed that early morning and night attacks were more likely to be fatal.

Still, no one is sure why asthma gets worse at night, says Stephen Shea, director of the Oregon Institute of Occupational Medicine at Oregon University of Health and Science. “Most people sleep at night, so maybe sleep causes worsening asthma at night,” he says. Or it can be caused by body position or mites or allergens in the litter. Or, Shea adds, “maybe it’s the body’s internal clock.”

This body clock is also called a circadian system. Among other important functions, it regulates hormones, heart rate and the immune system for about 24 hours. While this system is internal, it is strongly influenced by external factors such as light and dark, meal times and work schedules.

Historically, it has been impossible to isolate the role of the circadian system from human behavior and environmental risks, “because they go hand in hand,” said Frank Scheer, director of the Brigham and Women’s Hospital’s Medical Chronobiology Program. “You can’t know what actually causes changes in lung function.” But in a document published this month in Notices of the National Academy of Sciences, a team led by Scheer and Shea finally found a way to separate the circadian system from all external factors that could contribute to asthma.

First, they had their 17 study participants, all of whom had previously been diagnosed with asthma, monitor their lung function at home during their daily lives. Four times a day, participants used a hand-held spirometer to check how much air they could expel from their lungs in one second, a measurement called FEV1. (The more, the better.) They also record their symptoms and note when they should use their rescue inhalers.

Then things got significantly more involved. The same set of participants underwent two different experiments while living in dimly lit rooms at the Brigham Center for Critical Research and the Women’s Hospital. In an experiment called “routine routine”, participants sat in bed for 38 hours without being allowed to sleep. They could not get up to use the bathroom or do any heavy work. Every two hours they ate the same breakfast, a little peanut butter and jelly or a tuna sandwich. They were allowed to listen to books on tape, talk to nurses, or play card games, but they could not move, get excited, or get angry.

In these rooms without clocks or windows and with themes no longer tied to their daily work or home schedule, outside time felt as if it did not exist. Participants had no idea when the sun was rising or setting, when it might be time for lunch, or when they needed to fall asleep.