Asthma symptoms (wheezing, cough and shortness of breath) are called nocturnal asthma if they occur at night. For many people, night is the time that asthma is most active. When this is the case, symptoms typically occur between midnight and 8 a.m., especially around 4 a.m. Nocturnal asthma is not always obvious to doctors, and it is underreported by patients. Symptoms may be mistaken for other medical problems that can be active at night, including congestive heart failure, gastroesophageal reflux, a breathing problem called obstructive sleep apnea or another respiratory problem.
This type of asthma is common. One study of 8,000 asthmatic patients showed that about half had nighttime symptoms during most nights, and two in three had nighttime symptoms at least three times a week. Frequent nocturnal symptoms are a sign of poorly controlled asthma and should be discussed with your doctor.
Nocturnal asthma is usually due to a combination of several factors:
- Allergens are present in house dust and bedding (both contain debris from dust mites). When you shift position on top of your pillow and mattress, you can stir up a small "cloud" of dust mite allergens, which circulate near to your nose and mouth until they settle. It doesn't take very much dust mite allergen to trigger symptoms in a person who is allergic, particularly when they are concentrated right around your nose.
- Pet dander (if pets are kept indoors) and pollens (that can enter open windows, or can recirculate into the air from discarded clothing that was worn outside, if it has not been placed into a hamper) are other a common "bedroom" triggers for nocturnal asthma.
- Sometimes nocturnal asthma results from daytime exposure to allergens that cause a delayed attack hours later.
- Airway secretions can contribute to nocturnal asthma; about 70 percent of asthmatics have chronic sinusitis and/or postnasal drip. Clearing the sinuses could improve both daytime and nighttime symptoms.
- Sleep apnea, a condition in which breathing momentarily stops during sleep, also may occur in people with asthma. Although sleep apnea is an upper-airway disorder, it can trigger reflexes that result in an attack in the lower airways.
- Circadian rhythms — your body clock — may play some role. Circulating blood levels of epinephrine and steroids, both of which protect against asthma, are lowest between 4 and 8 a.m., leaving patients especially vulnerable at that time.
If you have symptoms that may be caused by nocturnal asthma, you should call your doctor for an evaluation and advice.