There were about 21 million low-wage breadwinners in the United States in 2011, according to a forthcoming study by University of Massachusetts Boston economists Randy Albelda and Michael Carr, CNNMoney reported. Over the last 30 years, the number of all U.S. workers has grown 40 percent, roughly in line with the adult population. But over that same time period, the number of low-wage workers who also live in low-income households has climbed 94 percent. "Increasingly, the people who are low wage workers -- they're not just teenagers or spouses -- they're workers whose families depend on them," Albelda said.