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The factors that contribute to nocturnal asthma remain a bit of a mystery. Experts believe a person’s internal body clock (circadian rhythms) may play a role. Certain body functions ebb and peak at various times over a 24-hour period. For example, lung function peaks in most people at 4 p.m. and is at its lowest point at 4 a.m. This latter time is a period when asthma attacks frequently occur, possibly because the body is more vulnerable to attack at that time.
This circadian cycle – sometimes called diurnal variation – depends on a person’s sleeping and waking cycle. Thus, a person who works at night and sleeps during the day is more likely to suffer from “nocturnal asthma” during daylight hours
Recent studies have also indicated that the hormone melatonin may play a key role in triggering nocturnal asthma attacks. Melatonin is a hormone produced by the pineal gland that helps regulate circadian rhythms such as eating and sleeping. However, recent studies suggest that melatonin also enhances allergic airway inflammation, making asthma attacks more likely. Melatonin is widely available in over-the-counter medications used to treat jet lag and insomnia. Experts suggest asthmatics avoid drugs containing melatonin until further information is available.
Other factors believed to contribute to nocturnal asthma include:
- Allergens. Pollen, pet dander, dust mites, cockroach debris and
 other household allergens frequently trigger nocturnal asthma. Sometimes, a delay occurs between the exposure to the allergen and the onset of asthma symptoms. Therefore, exposure in the evening hours may cause an asthma attack in the middle of the night. Additionally, allergen exposure, especially to dust mites, is highest in the bedroom.
- Airway inflammation. In some people with asthma, the airways become more inflamed at night as chemical levels change during the body’s natural circadian rhythms.
- Airway secretions. Chronic rhinosinusitis and postnasal drip are both believed to be contributing factors to nocturnal asthma.
- Airway cooling. Cold air is a known asthma trigger. Body temperature can drop rapidly during sleep, which may help to trigger an asthma attack.
- Heartburn (e.g., acid reflux, gastroesophageal reflux disease).
 For some people, lying down can cause stomach acids to drain into the tube leading from the throat to the stomach called the esophagus. The irritation and coughing that often result can trigger asthma symptoms. In some cases, successfully treating a reflux condition can lead to improvements in nocturnal asthma.
- Decreased strength of asthma medication. Patients who normally take asthma medications early during their daily routine may have lower levels of the medication left in their bodies prior to awakening. A physician can prescribe medications that will be strongest during periods when a nocturnal asthma attack is most likely.
- Sleep apnea. People with this disorder experience sudden momentary breathing cessation. This upper-respiratory disorder may cause reflexes in the lower airways that trigger an asthma attack.
- Obesity. Nocturnal asthma appears more often in patients who are obese.
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