A risk factor is something that is linked to an increased rate of a disease. Risk factors can be aspects of a person's lifestyle, such as diet, smoking, alcohol and exercise, or substances in the person's body or environment. For some risk factors a causal mechanism has been proven, which means scientists know how the factor causes the disease. For others there is only a correlation. Many diseases are caused by the interaction of several factors.
A diet high in saturated fat raises blood cholesterol, and smoking and a lack of exercise also increase the risk of cardiovascular disease. Obesity is a risk factor for Type 2 diabetes. Alcohol damages the liver and affects brain function. Smoking causes lung disease and lung cancer, and tar in tobacco smoke is a carcinogen. A carcinogen is a substance that causes cancer, and ionising radiation such as X-rays and gamma rays is also a carcinogen. Smoking during pregnancy can cause low birth weight, and alcohol during pregnancy can damage the brain of the unborn baby.
These diseases have a human cost, such as pain, a lower quality of life and early death. They also have a financial cost. An individual may lose income and pay for treatment, a local community loses workers and carers, a nation spends money on health care, and globally there is lost productivity. The effect of lifestyle factors can be seen in data at local, national and global levels. Because studies use samples, a large sample gives more reliable results, and information in tables, charts and scatter diagrams must be read carefully in terms of the risk factor.