Part Two. The urgent need for action
Chapter One. Chronic diseases: causes and health impact
The causes of chronic diseases
This section summarizes the extensive evidence on the causes of the chronic disease epidemics. The evidence comes from a full range of studies - laboratory, clinical and population-based - conducted in all regions of the world. The causes (risk factors) of chronic diseases are known; a small set of common risk factors are responsible for most of the main chronic diseases and these risk factors are the same in men and women and in all regions.
The common causes of the main chronic diseases
Common modifiable risk factors The causes of the main chronic disease epidemics are well established and well known. The most important modifiable risk factors are:
- unhealthy diet and excessive energy intake;
- physical inactivity;
- tobacco use.
These causes are expressed through the intermediate risk factors of raised blood pressure, raised glucose levels, abnormal blood lipids (particularly low density lipoprotein – LDL cholesterol), and overweight (body mass index ≥25 kg/m2) and obesity (body mass index ≥30 kg/m2). The major modifiable risk factors, in conjunction with the non-modifiable risk factors of age and heredity, explain the majority of new events of heart disease, stroke, chronic respiratory diseases and some important cancers. The relationship between the major modifiable risk factors and the main chronic diseases is similar in all regions of the world.
Other risk factors Many more risk factors for chronic diseases have been identified, but they account for a smaller proportion of chronic disease. Harmful alcohol use is an important contributor to the global burden of disease. It has been estimated to result in 3% of global deaths and 4% of the global burden of disease, almost half of which being the result of unintentional and intentional injuries. The relationship of alcohol use to chronic disease is complex. The health consequences of excessive alcohol use include liver cirrhosis (damage to liver cells); pancreatitis (inflammation of the pancreas); and various cancers, including cancer of the liver, mouth, throat, larynx and esophagus. On the other hand, current evidence from epidemiological and experimental studies suggests that a very low consumption of alcohol has a protective effect against the development of cardiovascular diseases. This protective effect only becomes important as the risk of cardiovascular disease increases in middle-aged and older people. At younger ages the adverse effects of alcohol use, especially violence and injuries, outweigh the benefits. Other risk factors for chronic disease include infectious agents that are responsible for cervical and liver cancers, and some environmental factors such as air pollution, which contribute to a range of chronic diseases including asthma and other chronic respiratory diseases. Psychosocial and genetic factors also play a role.