Asthma Patients Cautioned About Melatonin

"For patients whose asthma worsens at night, we found that higher levels of naturally occurring melatonin are associated with impaired lung function," said Dr. Sutherland. "Those findings, on top of previous ones linking melatonin to inflammation, suggest that all patients with asthma should avoid using melatonin supplements until more is known about their safety."

Melatonin, a hormone secreted by the pineal gland in the brain, is an important regulator of circadian rhythms in the body, especially sleep. It is released at night, generally beginning in the evening hours before bedtime, peaking in the middle of the night, and ending about the time people awaken. Because of its association with sleep, over-the-counter melatonin has become a popular dietary supplement sold as a treatment for jet lag and insomnia.

However, melatonin has also been shown to enhance inflammation in cell and animal studies of asthma. Airway inflammation is one reason people with asthma have difficulty breathing. A significant portion of asthma patients experience increased symptoms at night. Dr. Sutherland and his colleagues hypothesized that melatonin may play a role in this nighttime worsening of asthma.

The researchers had seven people with nocturnal asthma, 13 with non-nocturnal asthma, and 11 healthy controls establish a regular sleep schedule for seven days. On the eighth night, small blood samples were taken from the sleeping patients every two hours. These samples were evaluated for their melatonin levels. The study subjects also performed lung function tests before going to bed and after waking up.

The patients with nocturnal asthma had the highest levels of melatonin and the greatest drop in lung function overnight. Peak levels of melatonin averaged 67.5 picograms/milliliter in nocturnal asthmatics, 61.1 pg/mL in non-nocturnal asthmatics, and 53.5 in healthy controls. Lung function, as measured by the amount of air patients can exhale in one second (FEV1), dropped an average of 18.8 percent in nocturnal asthmatics, 5.1 percent in non-nocturnal asthmatics, and increased 1.5 percent in healthy controls. The correlation between overnight change in FEV1 and melatonin levels showed a strong 0.79 correlation in patients with nocturnal asthma. There was a slight, but not statistically significant, correlation among patients with non-nocturnal asthma.

"These findings suggest that melatonin naturally produced by people with nocturnal asthma increases inflammation in their airways, leading to worse lung function," said Dr. Sutherland. "Given that previous work has shown that melatonin promotes inflammation in the cells of both nocturnal and non-nocturnal asthmatics, any person with asthma should be cautious about taking supplements that would further raise their melatonin blood levels."