Sibling relationships may affect a child's weight, according to a recent study.

It is well documented that children with obese parents are at greater risk for obesity, however, researchers from Massachusetts General Hospital, Cornell University, and Duke University discovered a link between having an obese sibling and a child's obesity risk, after adjusting for the parent-child relationship.

They also found that the obesity status of a younger child's older sibling is more strongly associated with a child's obesity than is the parent's obesity status.

"The family environment is known to exert a strong influence on the trajectory of children's health, and prior research has done a great deal to illuminate connections between parent and offspring obesity. Others have also found that obesity is also often correlated between siblings," Mark C. Pachucki, lead investigator of the study, said in a statement. "Our study extends these findings by integrating data on both parent-child, and sibling relationships."

For the study, researchers surveyed more than 10,000 American households.

Based on their findings, the likelihood of childhood obesity varies with the number of children in a household, as well as their gender. According to the study, in a single child household, a child is 2.2 times more likely to be obese if a parent is also obese.

However, in families with two children, the data showed a stronger relationship with sibling obesity than with parental obesity. Older children in a two-child household with an obese parent are 2.3 times more likely to be obese, but that number jumps to 5.4 times for those with overweight younger siblings. If the child is the younger sibling in a two-child household, parental obesity is not relevant to risk, but having an obese older sibling is associated with a 5.6-fold higher risk.

The findings also uncovered a link between gender and obesity risk. In homes with only one child, girls were less likely to be obese than their male counterparts. Gender was also an important factor for siblings in two-child households. The study suggests that younger children may be particularly susceptible to the influence of an older sibling, especially if that sibling is of the same sex.

Researchers said the new study offers key data that will be beneficial in the fight against childhood obesity.

The findings were recently published in the American Journal of Preventive Medicine.