The study also found that siblings have twice as much influence than parents over performing good deeds.

Two Young Girls Sisters Hugging Back
Credit: Jasper Cole/Getty Images

While it may be hard to believe when your sister is wearing your favorite sweater without asking—again—there’s scientific research showing that having a sister is good for your mental health. (That sound you hear is a thousand younger sisters laughing uproariously at the very idea of this.)

Researchers from Brigham Young University studied 395 families from Seattle with two or more children, where at least one child in each family was between the ages of 10 and 14 and made a somewhat stunning revelation. "Just having a sister led to less depression," said Laura Padilla-Walker, a professor at Brigham Young University and lead author on the study, which was published in the Journal of Family Psychology. The researchers found that having a sister can help prevent tweens “from feeling lonely, unloved, guilty, self-conscious, and fearful.” The boost that siblings, particularly sisters, give to a youngster’s mental is even more of a boost than what their parents can manage.

The research found that siblings have a positive influence on each other no matter how old they are, their gender, or how many years they are apart. "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. While brothers or sisters can help younger siblings feel happy and secure, it was strongest with sisters. According to the study, having a sister prevents depression more than having a brother, which the researchers believes may be because girls are better at talking about problems or are more likely to take on a caregiver role.

And while affectionate siblings had the most protective effect on younger family members, affection was not required. For those of us with annoying sweater-swiping sisters, according to the researchers, even fights can help siblings form important life skills, like how to better control emotion. “[Fights] help you develop social skills, like communication, compromise and negotiation,” says Alex Jensen, assistant professor in the School of Family Life at Brigham Young University and the co- author of research into sibling relationships. “Even sibling conflict, if it is minor, can promote healthy development.”

The study also found that siblings have twice as much influence than parents over performing good deeds — including volunteering, doing favors for others and being nice to people.