Image: Senior man looking sad © George Doyle, Stockbyte, Getty Images

Katrina Depriest-Dark, age 58, who is handicapped and on disability, is grateful that her 80-year-old mother moved in with her this past year to help pay half of her $886 monthly mortgage on her Richmond, Va., home. As a single mother of now-grown children, Depriest-Dark found it costly to live alone, scraping by on disability checks and paying high medical costs to treat her lupus, diabetes and rheumatoid arthritis. She said she tried to buy in bulk, getting her groceries at Sam's Club, but with one person, much of that food would go to waste.

More Americans are living alone now than at any other point in history, and one-third of those 32.7 million are older than 65. A rise in the divorce rate in the over-50 set, which has doubled over the past two decades, along with women outliving their spouses by five to six years, is fueling the trend, which will only grow with an aging boomer population.

The older population in 2030 is projected to double from the start of this century -- from 35 million to 72 million -- representing nearly 20% of the total U.S. population, according to AARP.

Living on your own can be far more costly than sharing expenses like food and housing with a spouse, relative or housemate. Single seniors who also face escalating health care costs are five times more likely to live in poverty as their married peers. (Are you saving enough for retirement? Find out with MSN Money's calculator.)

A study by the Heller School for Social Policy and Management at Brandeis University, "Living Longer on Less: The New Economic (In)Security of Seniors," (.pdf file) found that only 31% of senior couples are economically secure, a number that drops to 16% for single seniors. "The trends are not great. They're going in the wrong direction," said Tatjana Meschede, one of the study's authors and the director of research at the Heller School.

A National Council on Aging analysis of data from The American Community Survey shows that a senior living alone spends almost 35% of his or her income on housing, compared with 22% if living with others. "There is an economy of scale when you live with two or more," says Hector Ortiz, a senior program associate for research at The National Council on Aging. While seniors with the benefit of a hefty divorce settlement or significant assets from a deceased spouse are in better shape, others -- widows, in particular -- deplete their assets within a year of the loss of a spouse's income. "They can't keep up with regular expenses. It puts a big burden on those households," he says.

David Baxter, senior vice president of Age Wave, a research firm that specializes in the 50-plus population, expects boomers -- who have transformed nearly every other life stage -- to find innovative ways to address the financial challenges of senior singlehood. "We'll see new ways of living single," with more communal living that offers both caregiving and opportunities for social interaction, he says.

Some single seniors are turning to roommates and other alternative living situations. Bonnie Jackson, 64, of Chicago, contacted a local center of National Shared Housing Resources to help her rent out the two unused bedrooms in her home. She now gets $500 a month for each room and gives discounts to tenants who help her run errands or change light bulbs. Another woman in her late 50s formed her own community in Silicon Valley by buying two homes in a three-house enclave and renting her second property to two other single women.

Single by choice

Eric Klinenberg, a professor of Sociology at New York University and the author of the recent book "Going Solo," says that many older Americans, especially women, are single by choice. Many widows who have spent years ministering to the health care needs of a now-deceased husband are concerned about repeating that "brutal and unhealthy experience" and shun marriage, he says. Still, he says, "aging alone is especially challenging."

Women who live alone are more vulnerable than men are, since women typically spend less time in the workforce, pay less into Social Security and accumulate fewer assets. Being a single woman "is a factor determining poverty in old age," says M. Cindy Hounsell, the president of the Women's Institute for a Secure Retirement. She says that a single person lives on 80% of what a couple lives on, not the 50% you might expect. While the poverty rate for all women age 65 and older is 11.5%, that rate for single women is almost twice as high, at 19.1%.

In addition to food and housing, seniors face mounting health care costs, as they grow frailer and need to pay for assistance. They often cannot rely on family members to care for them, as grown children may live far away or be preoccupied with careers and their own families. Sandra Timmermann, a gerontologist at the MetLife Mature Market Institute, says that tasks like rides to doctor's appointments or getting groceries come at a hefty cost: an average of $19 an hour for companion services. Further, a personal emergency response system can cost $50 to install and $15 to $35 a month to monitor. "These little things can really add up," she says.

As for Depriest-Dark, having her mother as a roommate has been a benefit, even though she's taxed with assisting in her care. "When you're on a fixed income, it's very helpful to have someone to help you with the mortgage," she says.

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