(CNN) When it comes to our closest adult relationships, the ones we have with our siblings often take a back seat.
Parent-child relationships, romantic relationships and peer relationships hog our collective attention, but we're tethered to our brothers and sister far longer; for many of us, our sibling relationships are the longest-lasting ties we have.
In the best-case scenario, this means a built-in best friend for life, but often sibling bonds are fraught and messy. Adult rifts can surface even among siblings who were inseparable in their younger years.
Take Britain's Prince William and Prince Harry, for example, who will be reunited this week at the unveiling of a memorial to their late mother, Diana, Princess of Wales. The two brothers were once close, but they now live on separate continents and are said to be barely on speaking terms.
It may be worth spending the time to repair those bonds, because experts say an emotionally intimate relationship with a sibling can make our lives happier and healthier.
"Sibling relationships are so important, but they are often overlooked," said Jonathan Caspi, a professor in the department of family science and human development at Montclair State University in New Jersey. "If you feel like you are grounded and connected to your family of origin, they are like your home base. You've got these people you can always come back to."
In the United States, nearly 8 in 10 children lived with a sibling -- whether biological, adopted or step brothers and sisters -- in 2014, according to US Census data.
Much research on sibling relationships focuses on children -- interactions between brothers and sisters when they're young are developmentally important. These relationships allow children to try out new social and emotional behavior, particularly when it comes to conflict. Siblings help each other learn ways to manage emotions and develop awareness of other people's thoughts and feelings.
The adult sibling relationship has been the subject of attention only sporadically, but existing research suggests there are clear benefits to maintaining and growing those connections over time. They pay dividends, particularly as we get older.
Sibling closeness first emerged as a surprising "sleeper variable" for emotional well-being in adulthood in the long-running Harvard Study of Adult Development, which began in 1937 and included 243 Harvard undergrads, the researchers said. Of the men in that study who were close to a sibling in their youth, 93% were thriving at age 65 -- medically, economically, physically and psychologically, Caspi noted in his research.
A 1999 Swedish study came to a similar conclusion. Contact with a sibling was more influential than friends or one's own children for good health and life satisfaction at age 83 and above. This was partly due to the fact that the number of friends decreased during this stage of life, but also reflects the importance of an emotionally close relationship with a sibling. They are a fellow traveler in life and a unique link to one's past, Caspi said.
Poor sibling relationships in childhood may also be linked to major depression in adulthood, according to one 2007 analysis. In a 2012 article in the journal International Sociology, information on 6,630 Dutch individuals showed that people who experienced serious negative life events like divorce, addiction, financial problems or psychological problems had a history of less supportive and more strained ties with their siblings.
Laurie Kramer, a professor of applied psychology at Northeastern University in Boston, said it is difficult to untangle the reasons for these apparent links.
"People seem to be healthier, happier and better adjusted -- all of those things are related to having positive relationships with siblings, you know, and a lot of that comes from this idea that you can get support and help and validation from having someone close to you who shares a history and understands the world in a similar way to you," Kramer said.
"What we don't really know is the root cause, whether it is that happier people are less depressed people and are better able to form positive relationships with siblings or having a great sibling relationship is helping people better cope with all the things that life throws at you."
Siblings share about 50% of their genes, so there is an evolutionary logic to investing and being interested in a siblings' welfare, Caspi said. He said this may explain the playground phenomenon in which siblings actively protect each other against bullies, but still torment one another in the same ways at home.
Plus, it's important to remember the way you behave with your siblings sends a message to the family you create as an adult, said Geoffrey Greif, the coauthor of "Adult Sibling Relationships" and a professor at the University of Maryland School of Social Work.
For example, a flash point in many strained sibling relationships is when elderly parents get ill. Often it can be difficult to sit down together and work out the way best to care for them, without evoking old rivalries and resentments about who was perceived to be the favored child.
"Think about what is the legacy you want to leave to your own children and family," Greif said.
If your adult relationship with your sibling is strained, here are some steps you can take to get along better.
Broaden your relationship and create new memories. Kramer said one common theme among siblings who don't report a good relationship is that they don't get together on their own terms. Often, they only see one another at family get-togethers organized by parents or other family members, when it's easy to gravitate to old roles and positions.
"There's something powerful about the family system that pulls you back into old communication patterns." She suggested finding ways to have rewarding and fun encounters beyond the family home.
Be accepting and let go of old resentments. Don't assume you know who your sibling is based on who you thought they were as a child. Understand the ways in which you are similar and different and find common ground in your shared experiences. One barrier to closeness in adulthood is a parent who played favorites, or was perceived to have played favorites, among siblings in childhood.
"Every family member has a different perspective on who was favored and why. As adults, I see this as a great opportunity for people just to bluntly talk about what they remember from that time and what they felt," Kramer said.
Don't compare yourself to your sibling. Just as when your younger brother got a bigger slice of cake, it might not seem fair that, as an adult, they end up with a better job or bigger house. But these are old feelings that don't stand up to honest scrutiny. We all make different choices, and there's no innate reason your path should be similar to your sibling's.
For parents who want to foster a strong bond between their kids that will support them for life, here are some tips:
Schedule one-on-one time. It might sound counterintuitive, but consciously scheduling one-on-one time with your children is a good strategy. It means that there is no competition for your attention, and you can praise (or correct) behavior without an audience or having the other child ascribe meaning to it.
Parent the positive behavior. It's important to make the effort to praise siblings when they are cooperating and playing nicely and not just get involved when the bickering makes its way to your ears.
Think about how you intervene in fights. It can be helpful to ignore simple bickering, but if fights get nastier, parents should play the role of mediator or problem-solving coach, not referee. Parents tend to intervene on behalf of the younger child, which builds more resentment in the older one and empowers the younger to challenge the older sibling more frequently.
Avoid phrases like "You're bigger, be nice!" "Be a good role model," or "She's little, let her have the toy."
Don't compare your children. They hear the comparisons, and it creates more competition and fighting.