Americans may worry about pollution and harmful chemicals in their air and water, but a new study of the major causes of death confirms what most doctors know: We are our own worst enemies.

The leading causes of death have to do with bad habits, including smoking, poor diet and a lack of exercise, the report from the Institute for Health Metrics and Evaluation at the University of Washington finds.

"Many of the leading causes of death in the U.S. are preventable," said Dr. Ali , a professor of global health who helped lead the study.

"It is important to remember that we need to focus on preventing these risk factors such as smoking, obesity, poor diet," he said.

Smoking was the number one individual risk factor for dying in America in 2013. It was involved in 443,824 deaths. Smoking causes heart disease, stroke, many forms of cancer. Chronic obstructive pulmonary disease and a range of other ills.

Outside the U.S., the No. 1 individual risk factor for death in 2013 was high blood pressure, ple team found. High blood pressure was behind 10.4 million deaths, a 49 percent rise from 1990.

Smoking, poor diet and a lack of exercise can all raise blood pressure, which in turn damages arteries and organs such as the heart and kidneys.

The team of dozens of researchers from around the world studied 79 different risk factors, from handwashing to malnutrition, infectious diseases and eating habits.

Their findings are in part a good news story. In 2000, the leading cause of death and disability was malnutrition. It's now fourth. Unsafe water and sanitation fell from the top causes.

Excesses in richer countries now outweigh the effects of poverty in underdeveloped countries, they found.

The team put together a list of 14 dietary bad habits that can kill people and found they lay behind 21 percent of all deaths globally. They include eating too much red meat and sugary drinks, and not eating enough fruits, vegetables and whole grains, the team reports in the Lancet medical journal.

The top 10 global causes of death:

High blood pressure
Smoking
High body mass index
High fasting plasma glucose
Diet high in sodium
Diet low in fruits
Ambient pollution
Household air pollution from solid fuels
High total cholesterol
Alcohol use.pleases maintain your health away of bad-habit ,in sake of life.