Being extremely overweight--100 pounds or more over your healthy weight range--cuts your life expectancy by 10 years, a new study from Oxford University in England found, according to USA Today's website.

The study analyzed nearly a million people and found that carrying around anything over 40 pounds of extra weight begins to shave away at your life, mainly by putting you at risk for heart disease and stroke. The effect is similar to lifelong smoking, said Professor RichardPeto, a professor of medical statistics at Oxford and one of the lead researchers on the study.

"Obesity causes heart disease and stroke by pushing up blood pressure, mucking up blood cholesterol and triggering diabetes," explained Gary Whitlock, co-author of the study and an epidemiologist at the University.

In America, almost everyone's at least moderately overweight. Sixty-six percent of adults are overweight or obese and over one-third of adults are obese.

Obesity is defined by a person's body mass index, or BMI. A BMI of 30 or more puts you in the obese category (click here to calculate yours).

Richard and his colleagues analyzed data from 56 studies that examined 900,000 people and 70,000 deaths over 10 to 15 years. Most of the study participants were either American or Western European.

Other revelations included the effects of being overweight, even if you are not obese. A BMI of 25 to 29.9 might strip one year from your life. Also, for every five-point BMI increase, your risk of early death increases by approximately 30 percent.

"[This study] provides a much clearer picture of the risk associated with various levels of being overweight or obese," said Michael Thun, epidemiological research emeritus vice president of the American Cancer Society. "What is particularly worrisome in the United States is that more than a third of people now qualify as obese, and a subset of people are becoming progressively more obese. Once you gain weight, it's hard to lose it and easy to gain more. So the goal [is] to stop your weight gain now."

-- Whitney Teal

Here's more:
What's in a BMI?
Black women at higher risk of stroke