Breathing requires adequately functioning lungs and respiratory muscles. The thoracic muscles (primarily the diaphragm and intercostal muscles) expand the chest and create a vacuum, causing air to enter the lungs. Once in the lungs, the oxygen in the air diffuses into the blood through thousands of tiny sacs called alveoli. The majority of oxygen then binds to hemoglobin in red blood cells so that it can be delivered to tissues throughout the body. Simultaneously, carbon dioxide that is produced by cells reenters the bloodstream and diffuses out of the alveoli, where it is exhaled.

Various diseases can affect the different tissue types in the lungs or the chest wall and have different causes (e.g., environmental, infectious, malignant, autoimmune, congenital). Such diseases include airway diseases (e.g., asthma, chronic obstructive pulmonary disease (COPD), acute bronchitis, cystic fibrosis, lung cancer), alveolar diseases (e.g., bacterial and viral pneumonias, tuberculosis, emphysema, pulmonary edema), diseases that affect blood vessels (e.g., pulmonary embolism, pulmonary artery hypertension ), diseases that affect the interstitium (e.g., pulmonary fibrosis, sarcoidosis, radiation pneumonitis); diseases that affect the pleura (e.g., pneumothorax, pleural effusion, malignant mesothelioma), and diseases that affect the musculoskeletal system (e.g., myasthenia gravis, amyotrophic lateral sclerosis, obesity hypoventilation syndrome).

Diet appears to play a role in the development, severity, and management of some respiratory diseases, especially when atopy (immune response) and airway inflammation are important factors (as is the case in COPD and asthma). Diet-related evidence is primarily sourced from epidemiological and some preclinical animal studies, but experimental human evidence is lacking. In general, high fruit and vegetable intake, a Mediterranean diet, and omega-3 fatty acid intake have shown benefits in respiratory diseases, whereas Western diets and fast food diets have shown adverse associations. ^[1]

Vitamin D, antioxidants (e.g., vitamin C, vitamin E, flavonoids, lycopene), and anti-inflammatory agents like curcumin have all been found by epidemiological and preclinical studies to be beneficial in asthma and COPD. N-Acetyl cysteine has been found to benefit patients with COPD due to its mucus-reducing and sputum-reducing effects, and it is also an essential part of management of cystic fibrosis.