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You know that close friendships feel good - but did you know just how much of a health boost they can be?

According to a 10-year study of older people in Adelaide, Australia, satisfying friendships predict longevity better than even close family ties, and they can protect against obesity, depression, and heart disease, among other health problems.

“When women get stressed, our instinct is often to find a friend and talk things through,” says Joan Borysenko, author of Inner Peace for Busy Women. “Both touch and talk release the hormone oxytocin, which has a profoundly calming effect on your mind and body.”

You don’t need 600 Facebook friends or a jam-packed social calendar to reap these impressive perks (in fact, both can backfire). Research shows the following “types” of relationships are especially potent for your health. Here’s how to cherish these friendships and make sure you stay close for the long haul.

Quiz: Are Your Friendships Healthy?

1. A Childhood Friend
She can still remember the boy-crazy, artistic girl you were at 16.

Longtime intimates are special for many reasons. They knew you and your family while you were growing up and likely have many memories and stories of you that no one else does. "These friends remind you that you are still the person you've always been," says Rebecca G. Adams, a leading friendship researcher and sociology professor at the University of North Carolina at Greensboro.

Nurture these ties by starting a members-only Web site—groups on Yahoo, Google, or Facebook are free and make it easy. Use them to plan vacations or share links to digital photo albums. Or keep things low tech—just stick a card in the mail now and then, and stay in touch with phone calls. Research from the University of Notre Dame shows that people who chat at least every 15 days have the best chance of staying close over time.

2. A New Friend
Unlike members of your grade school crew, newly acquired pals have no preconceived notions about you.

"As we get older, we can fall into ruts," says Pamela McLean, a psychologist in Santa Barbara, Calif. "New friends ignite different kinds of thinking and fresh ways of being." What's more, they'll connect you to another network of people, says Rosemary Blieszner, a professor at Virginia Tech who has researched friendships among older women. That network can be helpful if you’re looking to make a career change or find a new pool of potential dates.

Find new friends at the office, befriend your kids’ friends’ parents, or try new activities, like that Zumba class at the gym.

3. A Workout Friend
She'll drag you out for a jog on days when you'd rather be parked on the couch.

Experts agree that exercising—whether walking, golfing, or salsa dancing—is one of the most important things you can do for your physical and mental health and longevity. And a good friend may be the glue that makes this healthy habit stick. A University of Connecticut study of 189 women ages 59 to 78 found that strong social support was key to maintaining a new exercise regimen for 1 year.

For best results, set a joint exercise goal together—whether it’s going for a neighborhood walk 4 days a week or running a 5K. It's the best way to boost the get-healthy payoff of a workout partner because neither of you is poking and prodding the other, which is a recipe for resentment, says Marcia G. Ory, a researcher at Texas A&M Health Science Center.

5 Fun Outdoor Workouts to Do With A Friend

4. A Spiritual Friend
Being part of a spiritual community‚ not necessarily an organized religion‚ helps people stay resilient, research shows.

A study from Duke University Medical Center found that people who regularly attended religious services or engaged in activities such as prayer, meditation, or Bible study had a 50 percent lower risk of dying over a 6-year period than others of the same age and health status.

That's not to say it's easy to forge a connection in a room of 300 worshippers or while meditating on your own. Seek more intimate opportunities at a local church or temple: Volunteer in a canned food drive campaign, or attend a lecture series. Or try a neighborhood yoga center or community college; they often offer spiritually meaningful courses.

5. A Younger Friend
How did you juggle your full-time job and three kids? Your 10-years-younger friend really wants to know.

Research shows that an essential element of a happy life is to nurture and feel useful to others—by cooking a wholesome meal, say, or passing on what you've learned through experience. For many women, that itch gets scratched by raising children. But mentoring younger friends (from the office, for example) can give you that same feeling, Blieszner says.

To maximize the benefits of this friendship, let advice flow in both directions. A younger confidante can explain the social networking site du jour or offer a fresh take on current events.

6. Your Partner’s Friends
Becoming tight with your husband's pals is good for your marriage.

The more a couple's family and friends intermingle, the happier spouses are after even just 1 year of marriage, found one study that examined the social circles of 347 couples. "We were surprised," says researcher Kenneth Leonard, a professor of clinical psychology at SUNY Buffalo. "Including your spouse in your network of friends is nearly as important for marital happiness as making them feel they are a part of your family."

10 Habits of Happy Couples

7. Your Mom
About 85 percent of adult women say they have a good relationship with their mother, according to a Pennsylvania State University study.

Despite the inevitable conflicts between grown moms and daughters, the relationships are generally strong, supportive, and close. "There is great value in this bond because mothers and daughters care so much for one another," says study author Karen L. Fingerman. If you’d like to be closer but run into the same roadblocks over and over, here’s some advice to overcome the most common issues.

You find it hard to enjoy time with mom: Stop trying to change her, and focus on what you do enjoy, says Fingerman.

You keep clashing over the same old issues: The women who had the strongest relationships didn't take the conflicts personally. Instead, they tended to see criticism as a reflection of their mother's habits or traits.

The relationship feels too close for comfort: Daughters who did the best with this accepted that their mothers wanted more time together. Instead of telling their moms what they couldn't do, these daughters focused on when they could get together and what they could do for their mothers.

8. Yourself
If you're like a lot of women, you'd drop everything to help a friend in need‚ but often don't pay yourself the same respect.

So, how does one befriend herself, exactly? It starts with self-knowledge, says Prevention advisor Dr. Pamela Peeke, an assistant clinical professor of medicine at the University of Maryland. "Getting to know yourself is an amazing adventure," she says. "Think of what makes you fall in love with someone: how genuine, sincere, and caring they can be; the unconditional love they offer, no matter what. Doesn't that describe how you should feel about yourself?"

Peeke recommends you repeat the following mantra as a reminder: "I love and honor myself as I do the other important people in my life." To give yourself the TLC you deserve, write down seven things that make you feel happy and healthy (cooking dinner, talking to a friend, running, reading a book), and make sure you do at least one every day.

More Ways to Feel Happy: 14 Little Ways to Lift Your Mood