Have you ever noticed that it’s exactly in the company of a brother or sister that you can most easily be yourself? You can get angry, act silly, cry without explanations—and still be fully accepted. Most people treat these relationships as just a “given” of family life, but psychologists have long proven that sibling bonds are one of the strongest protective factors for mental health. And this profound, lifelong effect doesn’t stop in childhood.

Why Siblings Affect Us So Deeply

When we’re little, parents are the “big adults” who set rules and can sometimes feel intimidating because of their inherent authority. A brother or sister, on the other hand, is someone **almost your own size**—someone you can negotiate with, fight with, make up with, and co-create an entire world alongside.

Psychologists call these “horizontal relationships” (as opposed to the “vertical” ones we have with parents). In these horizontal bonds, a child learns three of the most important life skills for the first time:

• Regulating emotions through negotiation rather than obedience (“if you give me the toy car now, tomorrow I’ll let you play with my doll”).
• Seeing yourself through the eyes of another person who has known you since you were in diapers and **won’t sugar-coat things** out of politeness.
• Forgiving and being forgiven—because tomorrow you’ll still have to play together and the relationship is a given.

That’s why children who grow up with siblings usually show better emotional regulation and higher empathy as early as preschool age.

What the Research Actually Says (Some Fascinating Numbers and Findings)

A 2010 Brigham Young University study (over 400 adolescents) found that warm sibling relationships reduce the risk of depression by 20–25% even when the parent-child relationship was difficult or conflictual. In other words, a brother or sister can partially “compensate” for less-than-perfect parenting.

A large, 15-year longitudinal study at Penn State University (over 200 families) showed that kids who had an older sibling were, on average, better at handling school bullying. The reason is simple: at home they’d already gone through “conflict training” and learned how to stand up for themselves effectively.

In adulthood, people who maintain close ties with their siblings experience lower levels of loneliness and greater resilience to stress (Journal of Family Psychology, 2019).

And here’s a particularly heart-warming discovery: when there’s an older sister in the family, younger children (both boys and girls) tend to show higher levels of compassion and softer conflict-resolution styles. Big sisters literally teach the whole family emotional literacy.

Why it Works Even If You “Hated” Each Other As Kids

Most of us remember fighting over the remote or the last slice of cake. But here’s the paradox: those very conflicts are the **training ground**. When you scream “I hate you!” at age eight and an hour later you’re building a pillow fort together, you’re learning that intense emotions and closeness can coexist. That’s an invaluable lesson for life, especially in maintaining other deep relationships.

People who grew up as only children often say: “That’s exactly what I missed—someone I could be ‘bad’ with and still be **loved unconditionally**.”

And What About Old Age?

The longest-running studies of human happiness (one of them, the **Harvard Grant Study**, has been going since 1938) show that the single best predictor of well-being and health at age 80+ isn’t career success or money—it’s the **quality of close relationships**. And very often, the person who has known you the longest on this planet is your brother or sister. They’re like an **anchor** to your personal history and identity.

A Tiny Experiment You Can Do Right Now

Think of one ridiculous shared memory with your sibling that made you both laugh until you cried. Got it? Notice how warm it feels inside. That’s the “sibling effect” still working decades later and across thousands of miles.

So if you have a brother or sister—send them something nice today. Even if you only see each other once every five years. Science says it’s literally an investment in your shared mental health. And if you’ve been estranged for a long time, that’s even more reason to reach out. After all, you two have been practicing how to make up better than anyone else—you’ve been **training your whole childhood**.

Because sometimes the most powerful therapy is simply the person who remembers exactly what you looked like at age five when you cut your own bangs.

Sources:

• Whiteman, S. D., McHale, S. M., & Soli, A. (2011). Theoretical perspectives on sibling relationships. Journal of Family Theory & Review.
• Feinberg, M. E., et al. (2012). Sibling relationships and influences in childhood and adolescence. Journal of Marriage and Family.
• Brigham Young University study on siblings and adolescent mental health (2010).
• Journal of Family Psychology research on adult sibling ties and resilience (2019).
• The Harvard Grant Study (1938-present).