The nation's increasing number of single-person households are feeling the strain of balancing their living expenses with saving for retirement, according to a new study.

Single-person households say they're most concerned about their ability to pay living expenses (53 percent) and medical expenses (49 percent), according to The New American Family: The MetLife Study of Family Structure and Financial Well-Being by the MetLife Mature Market Institute and the Society of Actuaries.

More than half of the respondents say they fear changes in Social Security and Medicare that will reduce their retirement resources. Longevity also poses risks with roughly 45 percent of the households polled, who say they might not have enough money to pay for health care or a long-term stay in a nursing home as they age.

Respondents said meeting day to-day household financial expenses has taken a toll on their ability to save for the future. Forty percent of those polled indicated that they are behind on their plans to save for retirement.

Respondents cited several external factors contributing to their household financial anxieties, including future tax increases, changing interest rates, stock market fluctuations and reductions in pensions and annuities.

The number of single-person households in America has been steadily increasing. According to the latest U.S. Census figures, there were 31 million single-person households in the U.S. in 2010, up 15 percent since 2000 and four times more than the seven million in 1960.

Married couples now represent 48 percent of American households, the first time that figure has been less than half since data collection on families began in 1940. Only 20 percent of all households in the U.S. are married couples with children.

"While couples are better off financially and more prepared to confront financial challenges, the economy is affecting almost everyone and there is a societal need to address what may be a crisis in the coming years as the population ages and these trends continue," said Sandra Timmermann, director of the MetLife Mature Market Institute.

Conducted by GfK Custom Research North America on behalf of Metlife, the survey queried 2,500 adults age 45-80 between Feb. 8 and 19.

-Jim McConville