The probability that a Russian man will die before he turns 55 is 25 percent.

Russia’s life expectancy is exceptionally low compared with that in other developed countries. While American men have a 1-in-11 chance of dying before their 55th birthday, in Russia the odds are 1 in 4.

The main reason, two large studies suggest, is vodka.

Starting in 1999, an international team of researchers interviewed 151,000 Russian adults. Ten years later, they sought out the same people. About 8,000 had died.

The researchers calculated the risk of death based on the participants’ originally reported vodka consumption, and they controlled for factors including age, smoking and education.

Male smokers who reported drinking three or more half-liter bottles of vodka per week had a substantially higher risk of death than those who reported drinking less than one bottle a week, the team reported recently in The Lancet.

“The main reason for the extraordinary difference in premature death between Western and Eastern Europe is alcohol,” said an author of the studies, Richard Peto, a professor of epidemiology at the University of Oxford. “Russians are drinking spirits dangerously.”

Typically, Russian men drink their vodka neat. They also tend to drink until they are drunk, and then continue drinking.

Habits can change, however. Alcohol restrictions imposed by the Soviet leader Mikhail S. Gorbachev in 1985 were credited with a 25 percent drop in drinking and death rates. After the Soviet Union collapsed in 1991, consumption and deaths surged again.

More recent measures, including price increases and a crackdown on black-market sales, cut consumption by a third, and the death rate among men under 55 has fallen to the present 1 in 4, from 1 in 3.

“There’s not 10 or a hundred things Russians should worry about changing — just those two things: drinking and smoking.” Dr. Peto said.