Teenagers with more siblings have worse mental health, study suggests

The researchers asked 9,100 eighth graders in the US and 9,400 in China, with an average age of 14, a range of questions about their mental health. Photograph: Design Pics Inc/Alamy

From Cain and Abel and the Brothers Karamazov to Cinderella, the warmth and support provided by siblings has hardly been taken for granted.

Now, researchers have found that children who moan about their brothers and sisters may have good reason to complain: the more siblings teenagers have, the more it hits their happiness, they claim.