A five-year study of 2,512 men living in Caerphilly (Wales) showed that eating five apples a week can increase lung capacity by an average 138 millimetres. Originally it was thought that a diet generally high in citrus fruits, fruit juices and vitamins A, C and E would benefit the lungs but, after adjusting for other factors, it was only possible to form a significant link with apples and vitamin E.

The researchers believe that the beneficial effect may be due to quercitin, an antioxidant which abounds in (e.g.) apples, onions, tea and red wine.