Food and Fitness: asthma

A respiratory disorder characterized by recurrent attacks of difficulty in breathing (described in medical books as ‘episodic wheezing’), particularly on exhalation. It is caused by an increased resistance to air flow through the respiratory bronchioles (small air tubes leading to the lungs). Sufferers are hypersensitive to a variety of stimuli (e.g. house dust mites; diesel exhaust particulates; and vehicle exhaust gases, such as ozone and nitrogen oxides) which cause the airways to narrow. Asthma may be induced by exercise and food allergies. Sports vary in their tendency to induce asthma, with running having a high tendency, cycling a moderate tendency, and gymnastics and swimming a low tendency. Paradoxically, many asthmatics gain relief from bronchospasms by regular exercise, and exercise is now seen as important in the management of asthma. Asthmatic attacks are relieved by a number of drugs, but competitive sports people should be aware that some of these are banned by sports federations because, as well as controlling asthma, they may act as artificial stimulants.

Adult-onset asthma

Allergenic materials may also play a role when adults become asthmatic. Asthma can actually start at any age and in a wide variety of situations. Many adults who are not allergic do have such conditions as sinusitis or nasal polyps or they may be sensitive to aspirin and related drugs. Another major source of adult asthma is exposure at work to animal products, certain forms of plastic, wood dust, or metals

Child-onset asthma

When asthma does begin in childhood, it often does so in a child who is likely, for genetic reasons, to become sensitized to common "allergens" in the environment (atopic person). When these children are exposed to house-dust mites, animal proteins, fungi, or other potential allergens, they produce a type of antibody that is intended to engulf and destroy the foreign materials. This has the effect of making the airway cells sensitive to particular materials. Further exposure can lead rapidly to an asthmatic response. This condition of atopy is present in at least one-third and as many as half of the general population. When an infant or young child wheezes during viral infections, the presence of allergy (in the child itself or a close relative) is a clue that asthma may well continue throughout childhood.

Description

About 10 million Americans have asthma, and the number seems to be increasing. Between 1982-92, the rate actually rose by 42%. Not only is asthma becoming more frequent, but it also is a more severe disease than before, despite modern drug treatments. In the same 10-year period, the death rate from asthma in the United States increased by 35%.

The changes that take place in the lungs of asthmatic persons makes the airways (the "breathing tubes," or bronchi and the smaller bronchioles) hyper-reactive to many different types of stimuli that don't affect healthy lungs. In an asthma attack, the muscle tissue in the walls of bronchi go into spasm, and the cells lining the airways swell and secrete mucus into the air spaces. Both these actions cause the bronchi to become narrowed (bronchoconstriction). As a result, an asthmatic person has to make a much greater effort to breathe in air and to expel it.

Cells in the bronchial walls, called mast cells, release certain substances that cause the bronchial muscle to contract and stimulate mucus formation. These substances, which include histamine and a group of chemicals called leukotrienes, also bring white blood cells into the area, which is a key part of the inflammatory response. Many patients with asthma are prone to react to such "foreign" substances as pollen, house dust mites, or animal dander; these are called allergens. On the other hand, asthma affects many patients who are not "allergic" in this way.

Asthma usually begins in childhood or adolescence, but it also may first appear during adult years. While the symptoms may be similar, certain important aspects of asthma are different in children and adults.