A non-communicable disease is not caused by a pathogen, so it cannot be passed from one person to another. Many of these diseases do not have a single cause. They are usually caused by the interaction of a number of factors, such as the genes a person inherits, their diet, how much they exercise, whether they smoke, how much alcohol they drink and the environment they live in.
Examples include cardiovascular disease, many forms of cancer, some lung diseases such as bronchitis and some liver diseases such as cirrhosis. Smoking and air pollution can damage the lungs and lead to bronchitis, and drinking a lot of alcohol over many years can damage the liver and lead to cirrhosis.
Some diseases are influenced by nutrition. Type 2 diabetes is one, and it is more likely in people who are overweight or have a poor diet, although genes also play a part. Because several factors act together, a person with one risk factor may not get the disease, and a person with several is more likely to.