People across the world are falling so far short on exercise that the problem has become a global pandemic, causing nearly a tenth of deaths worldwide and killing roughly as many people as smoking, researchers warned this week as an alarming series of studies was published in the Lancet.

Eight out of 10 youngsters age 13 to 15 don't get enough exercise, according to one of the Lancet studies released Tuesday, and nearly a third of adults fall short. The problem is even worse for girls and women, who are less active than boys and men, researchers found.

The results are fatal. Lack of exercise is tied to worldwide killers such as heart disease, diabetes and breast and colon cancer. If just a quarter of inactive adults got enough exercise, more than 1.3 million deaths could be prevented worldwide annually, researchers said. Half an hour of brisk walking five times a week would do the trick.

Despite its deadly consequences, lack of exercise doesn’t get the same funding or attention as other health problems, said Pedro Hallal, associate professor at the Federal University of Pelotas in Brazil and author of one of the studies.

“It gets underfunded and undervalued,” Hallal said. “But it’s huge everywhere in the world.”

In the widest study ever of the scope of the problem, Hallal and his fellow researchers found that although wealthier countries are more likely to fall short on physical activity, people in countries across the globe are getting too little exercise. The new research covered 122 nations representing 89% of the world's population.

The affluent Mediterranean island nation of Malta, for instance, had the highest rate of adult inactivity reported in the study, with more than 7 of 10 adults failing to get enough exercise. Close behind was Swaziland, a developing country between South Africa and Mozambique.