Exercising for 15 minutes every day can extend a person's lifespan by an average of three years, researchers in Taiwan have found.

Following more than 400,000 people over eight years, the Taiwanese study concluded that working out just half as much as most doctors recommend is significantly better than sitting around.

The U.S. Centers for Disease Control and Prevention say Americans need to exercise 150 minutes per week, with additional strength training. That rounds out to about 30 minutes a day, and only one third of Americans are currently meeting that standard.

"The 30-minute-a-day for five or more days a week has been the golden rule for the last 15 years, but now we found even half that amount could be very beneficial," lead author Dr. Chi-Pang Wen told ABC News. "As we all feel, finding a slot of 15 minutes is much easier than finding a 30-minute slot in most days of the week."

Those who achieve a 30-minute per day average can expect to live four years longer than those who do less than one hour of moderate activity per week, the study also found, and each additional 15-minute spurt "reduces the risk of death" by 4 percent.

The study was published in the journal The Lancet. According to the report, more than half those surveyed can be classified as "inactive."