Lifestyle affects the risk of non-communicable disease. Obesity develops when a person regularly takes in more energy from food than they use, especially with little exercise. It is measured with the body mass index: BMI = mass (kg) ÷ (height (m)) squared. A person of mass 72 kg and height 1.8 m has a BMI of 72 ÷ 3.24 = 22.2. A BMI above 30 is classed as obese, and a BMI of 40 or more is severely obese. The waist to hip ratio is the waist measurement divided by the hip measurement. A high ratio means a lot of fat is stored around the middle, which raises the risk of cardiovascular disease and type 2 diabetes. Malnutrition is a diet that lacks the right nutrients or the right amounts of them, so it can mean too little food or an unbalanced diet.
Drinking a lot of alcohol over many years damages the liver, which has to break the alcohol down. Liver cells are damaged, fat builds up and scarring called cirrhosis can lead to liver failure. Smoking raises the risk of cardiovascular disease. Nicotine increases heart rate and blood pressure, carbon monoxide reduces the oxygen carried by the blood, and chemicals in smoke damage the lining of the arteries so that fatty deposits build up and narrow them.
The effects can be seen at three levels. Locally, a town with few parks and many fast food outlets may have more obesity. Nationally, diet and smoking related diseases cost health services such as the NHS a great deal and governments may respond with laws, taxes or campaigns. Globally, obesity and other non-communicable diseases are rising in many countries, while malnutrition is still common in others.