The number of underinsured and uninsured adults in the U.S. has gone up, research shows, but researchers at the Commonwealth Fund believe the Affordable Care Act will help alleviate the problem.

A new study shows that the number of underinsured adults in the U.S. rose from 16 million to 29 million from 2003 to 2010.

The study also shows that 81 million people were either uninsured or underinsured in 2010.

Researchers surveyed thousands of adults ages 19 and older about their health insurance situations.

Underinsured families are at nearly as high risk as the uninsured because, while they have health insurance, holes or limits in their plans expose them to often unaffordable medical costs, lead study author and Commonwealth Fund senior vice president Cathy Schoen said in a statement. To reduce the number of underinsured, it will be critical for the plans offered under the Affordable Care Act reforms to keep deductibles and out-of-pocket costs low for essential, effective health care.

Low-income families were most at risk for being uninsured or underinsured.

Middle income families were also at risk. Approximately 16 percent of adults who made between $40,000 and $60,000 annually were underinsured in 2010. Nineteen percent of people in this income range were uninsured.

The study found that 46 percent of underinsured and 63 percent of uninsured adults did not follow common medical advice, such as filling out prescriptions or seeing doctors when they were sick. They also went without recommended medical tests and treatments.

The majority of people surveyed, 52 percent of underinsured and 58 percent of uninsured adults, were either contacted by a collections agency over unpaid bills, changed their way of life to pay medical bills, or were in the process of paying off medical debt.

People with adequate health insurance were found to have far less stress than those who were underinsured or uninsured.

Inadequate health insurance puts families' health and financial security at risk, Commonwealth Fund president Karen Davis said. The good news is that the Affordable Care Act includes provision to improve coverage for everyone. If plans are well-designed to cover high-value care, in the future families won't have to live in fear of paying for health insurance that won't protect them when sick-families, especially low and middle income families, will have the greater security of knowing they can afford the health care they need.