People with asthma should consider limiting the use of melatonin as a sleep aid, according to researchers in the US, who report that higher levels of melatonin are associated with an overnight loss of lung function in asthma patients.
Melatonin, a hormone secreted by the pineal gland in the brain and released at night, is an important regulator of circadian rhythms in the body, especially sleep. Supplements of melatonin have become popular in the US as a treatment for jet lag and insomnia.
Dr Rand Sutherland and his colleagues from the National Jewish Medical and Research Center have previously shown that melatonin induces the release of chemicals that promote inflammation, a hallmark symptom of asthma.
"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."
For the study, published in the September 2003 issue of the Journal of Allergy and Clinical Immunology, seven people with nocturnal asthma, 13 with non-nocturnal asthma, and 11 healthy controls established 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 per cent in nocturnal asthmatics, 5.1 per cent in non-nocturnal asthmatics, and increased 1.5 per cent 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, reported the team.
"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," concluded Sutherland.