When Carol Marak was in her 30s, she asked herself whose life she wanted: her brother's – the life of a successful and well-traveled businessman – or his wife's – the life of a woman whose career better accommodated raising three children.

The answer was a no-brainer: "My brother was in a position I wanted," says Marak, now a 64-year-old editor at SeniorCare.com who lives in Waco, Texas. Although she had been married and divorced earlier in life, at that point she had no kids and "made a very conscious decision" to keep it that way, she says.

Plenty of Marak's peers did the same thing. According to a 2012 study in The Gerontologist, about one-third of 45- to 63-year-olds are single, most of whom never married or are divorced. That's a whopping 50 percent increase since 1980, the study found. What's more, about 15 percent of 40- to 44-year-old women had no children in 2012 – up from about 10 percent in 1980, U.S. Census data shows. "My career was No. 1 in my life," says Marak, who worked in the technology industry for years.

But today, Marak and her single, childless contemporaries are facing a repercussion of their decision that never crossed their minds as 30-somethings: "How in the world will we take care of ourselves?" she asks.

Dr. Maria Torroella Carney, chief of geriatrics and palliative medicine at North Shore-LIJ Health System in New York, is asking the same thing. In research presented this year at The American Geriatric Society's annual meeting, Carney and her colleagues found that nearly one-quarter of Americans over age 65 are or may become physically or socially isolated and lack someone like a family member to care for them. Carney calls them "elder orphans."

"The risk of potentially finding yourself without a support system – because the majority of care provided as we get older is provided by family – may be increasing," she says.

The consequences are profound. According to Carney's work, older adults who consider themselves lonely are more likely to have trouble completing daily tasks, experience cognitive decline, develop coronary heart disease and even die. Those who are socially isolated are also at risk for medical complications, mental illness, mobility issues and health care access problems.

"You could be at a hospital setting at a time of crisis and could delay your treatment or care, and your wishes may not be respected [if you can't communicate them]," says Carney, also an associate professor at Hofstra North Shore-LIJ School of Medicine.

Take "Mr. HB," a 76-year-old New York man described in Carney's research as "a prototypical elder orphan." After attempting suicide, he arrived at a hospital with cuts on his wrist, bed sores, dehydration, malnutrition and depression. He lived alone and hadn't been in contact with any relatives in over a year. His treatment was complicated, the researchers report, in part because he was too delirious to make clear decisions or understand his options. He wound up at a nursing facility with plans to eventually be placed in long-term care.

But growing older without kids or a partner doesn't mean you're doomed – just as aging with kids and a partner doesn't mean all's clear. "We're all at risk for becoming isolated and becoming elder orphans," Carney says. You could outlive your spouse or even your children, find yourself living far from your family or wind up in the caretaker role yourself if a family member gets sick. Keep in mind that 69 percent of Americans will need long-term care, even though only 37 percent think they will, according to SeniorCare.com.

Plus, there's no way around the natural physical and mental declines that come with age. "Everybody has to prepare to live as independently as possible," Carney says. Here's how:

1. Speak up.

Marak wishes she had talked more with her friends and colleagues about her decision not to become a mom early on. That may have given her a jump-start on anticipating various problems and developing solutions to growing older while childless. She advises younger generations to discuss their options openly with friends – married and single, men and women – before making a firm decision.

"We discuss our psychological issues with professionals. We discuss our money strategies with financial experts," Marak says. "Why not talk openly about family concerns and what it means to have or not have children? So many of us go into it with blinders on."

2. Act early.

How early you start planning for your future health depends partly on your current condition – and your genes, says Bert Rahl, director of mental health services at the Benjamin Rose Institute on Aging. "If your ancestry is that people die early, you have to plan sooner and faster," he says.

But whether you come from a family of supercentenarians or people who have shorter life spans, it's never too soon to save for long-term care, whether it's by investing in a home, putting aside a stash for medical emergencies or "whatever you can do to have a nest egg," Marak says. "Life is serious, especially when you get old. Don't get to [a point] when you're 60 and now you're having to scramble to catch up."

Still not motivated? "Everybody wants some control in [their] life," Rahl says. "If you don't plan, what you're choosing to do is cede that control to somebody else – and the likelihood that they're going to have your best interests at heart is a losing proposition."

3. Make new friends and keep the old.

Your social connections can help with practical health care needs, like driving you to the doctor when you're unable. But they also do something powerful: keep you alive, research suggests. In a 2012 study of over 2,100 adults age 50 and older, researchers found that the loneliest older adults were nearly twice as likely to die within six years than the least lonely – regardless of their health behaviors or social status.

Connections can also help ward off depression, which affects nearly 20 percent of the 65-and-older population, according the National Alliance on Mental Illness. "One of the things that keeps people from being depressed is to be connected," Rahl says. "The more social activities you have, the more friends, the more things you can do to keep your body and mind active – that's the best protection you have against mental illness."

4. Appoint a proxy.

Who is your most trusted friend or relative? "Identify somebody to help you if you're in a time of crisis, and revisit that periodically over your life," Carney suggests. Make sure that person knows your Social Security number, where you keep your insurance card, which medications you take – "the whole list of things somebody needs to know if they're going to help you," advises Dr. Robert Kane, director of the University of Minnesota’s Center on Aging.

Before you start losing any cognitive capacities, consider designating that person as your durable power of attorney for health care, or the person who makes health care decisions for you when you're no longer able.

If no one comes to mind, hire an attorney who specializes in elder care law by asking around for recommendations or searching online for highly rated professionals. Unlike your friends, they have a license to defend and are well-versed in elder care issues. Most of the time, Rahl's found, "they're trustworthy and will do a good job for you."

5. Consider moving.

Marak is on a mission: "to create my life where I'm not transportation-dependent," she says. She's looking to move to a more walkable city, perhaps a college town where she's surrounded by young people and can stay engaged with activities like mentoring. She also hopes her future community is filled with other like-minded older adults who can look out for one another. "I want to … set up my life where I'm not living alone and isolated," she says.

Adjusting your living situation so that you can stay connected to others and get to, say, the grocery store or doctor's office is the right idea, says Carney, who cares for a group of nuns who live communally and has seen other adults create communities that act like "surrogate families," she says. "Think: Where do you want to live? What's most easy? How do you access things? How do you have a support system?"

6. Live well.

Marak is lucky: She's always loved eating healthy foods and walking – two ways to stay as healthy as possible at all ages. "Some of the foods that we eat are really, really bad for the body," she says. "That's one of the major causes of chronic conditions – and not exercising."