Aug. 5, 2010 -- Long before she vowed to improve the health of American children, First Lady Michelle Obama made Craig Robinson a better person just by being his little sister Miche.
Simply by being a sister, Susan G. Komen inspired her sibling to be a more generous person too – eventually leading a worldwide crusade that has raised $1.5 billion for breast cancer research.
New research shows that having a sister – even one who pinches and tattles but also shares her ice cream cone – makes you a kinder, more giving person.
The study has found that adolescents with sisters feel less lonely, unloved, guilty, self-conscious and fearful. Regardless of whether she is older or younger, a sister has a far stronger influence than parents on a person's mental well-being.
"Just having a sister led to less depression," said Laura Padilla-Walker, a professor in Brigham Young University's School of Family Life and lead author on the study published in this month's Journal of Family Psychology.
For Robinson, head coach at Oregon State University, a close relationship with his only sibling Michelle, two years younger, included sharing a bedroom separated by a divider. Not only his roommate but his confidante, Miche, as he calls her, was upset that their parents smoked and once conspired with him to destroy every cigarette in the house.
Nancy Brinker and her sister Suzie, three years older, grew up as best friends. "Suzie was the Queen Bee of the neighborhood but she had her mischevious side. When she was grounded, I was the hostage negotiator. When she exceeded her curfew, I was the peace envoy. When Suzie died, my life's work was born," said Brinker, founder of Susan G. Komen for the Cure.
The study showed that brothers have benefits, too, as long as the relationship is more loving than combative.
"Sibling affection from either gender was related to less delinquency and more pro-social behaviors like greater kindness and generosity, volunteering and helping others," Padilla-Walker told ABC News.
In fact, the link between sibling affection and good deeds is twice as strong as the link between parental love and good deeds.
Growing Up With A Sister Makes You a Nicer Person
The study, in Seattle, Wash., involved 395 families with more than one child, including at least one aged 10-14. The adolescent child responded to a questionnaire and was videotaped while answering questions about a sibling closest in age. The process was repeated one year later.
Results revealed the importance of a loving sibling relationship, especially one built on making up after the bickering, noogies and wedgies have ended.
"Even if there is a little bit of fighting, as long as they have affection, the positive will win out," said Padilla-Walker. "If siblings get in a fight, they have to regulate emotions. That's an important skill to learn for later in life."
Padilla-Walker said her own young son and daughter "fight every 15 minutes but they make up. That's where parents come in. The key is to have kids learn to make up with one another before they have fights with their peers. It's important so that when they are adolescents they can have those skills."
The findings shed light on families around the world, since more than 80 percent of people in the developed world have at least one sibling, with two children in most families.
"Sibling relationships are the most enduring relationships people have. Parents die and you don't meet your spouse until later in life. So throughout life, siblings really remain important," said Padilla-Walker.
Celebrity siblings like reality TV's Kardashian sisters are a classic example of how sibling support has benefited people who would never have otherwise hit on stardom.
While the sibling factor cuts across racial and economic barriers, it loses strength in single-parent families, the study showed.
"In a single-parent family, the sibling may be taking on a parental role rather than the role of a confidant. The parent-child relationship is vertical, with the parent in charge. The sibling relationship is horizontal, you're on the same ground. That's a good thing because you can talk about what you're really feeling. There is no feeling of authority or being told you're doing something wrong," Padilla-Walker said.
"Once they hit adolescence they have someone to confide in," Padilla-Walker said. "They can get into stuff they don't feel comfortable discussing with others in the house."
The gift of gab may explain why sisters seem to improve their siblings' mental health. Padilla-Walker said previous research has shown that girls talk more than boys.
So having a sister in the house may be similar to having a therapist on call 24/7, even if it means whispering in the dark to the person who keeps shaking the bunk bed.