While the rat race ends with retirement, one of its principal features extends well past a person's last day of work.

Income inequality in the United States spills over from the job into the last decades of life, according to a new survey that ranks the differences among U.S. retirees as among the most extreme in the 35 country comparison.

The findings issued last week by the OECD, or Organization for Economic Cooperation and Development, reports levels of inequality in a survey of member countries.

The inequality among older people in the U.S. is among the most extreme, according to the report.

"Inequality has been growing from one generation to the next in the United States," according to the report. "This is particularly alarming... as old-age inequality among current [U.S.] retirees is already higher than in all other OECD countries, except Chile and Mexico."

The gap between the top and bottom incomes seems destined to rise, too.

Within each generation of workers, according to the OECD data, inequality rises. For example, researchers tracked U.S. income inequality for four different generations - people born in 1920, 1940, 1960, and 1980. For each group, inequality has been more extreme than the previous generation.

Alicia Munnell, director of the Center for Retirement Research at Boston College, said she was not surprised that the U.S. would rank at the extremes for income inequality.

"The big problem in the U.S. is that half of the working population in the private sector has no retirement plan available at work - and people do not save on their own," Munnell said. "Without any retirement saving, they only have Social Security, and Social Security is getting less generous over time."

According to the OECD report, one of the drivers of income inequality - from young workers to retirees - stems from the fact that so many Americans have simply stopped working.

"The United States is one of [a] few countries where employment among the prime working-age population is lower today than it was in 2000," according to the report.

More specifically, it noted that in 2000 about 82 percent of Americans between the ages of 35 and 44 worked; by 2016, that number had slipped to 79 percent. The shortfall of employment is most striking among workers at the bottom rungs. While more than four-fifths of the highly educated working-age population is actually working, the report says. Only about half of those with low education levels are.

While the inequalities among people of working age are a primary reason for inequalities among older Americans - the inequalities follow people into retirement, ill health is another critical source of difference. More than one in three American adults is obese, more than in any other OECD country, according to the OECD, and the ill health is concentrated among the poor.

"Americans are far more unhealthy than their peers in a number of other countries and people from low socio-economic backgrounds are particularly affected by bad health," according to the report. "Disabilities, depression and obesity are widespread."