The study found that obese 8 and 9-year-olds were more likely to suffer socially and emotionally than their normal-weight peers.
The study was conducted in Australia, and was led by Michael Gifford Sawyer of Women's and Children's Hospital in Adelaide.
Researchers checked the Body Mass Index (BMI) of children 4-5 years old, and then again in a couple of years. Parents and teachers filled out questionnaires that assessed children's mental health and health-related quality of life.
They found that kids with high BMIs -- meaning they were already either overweight or obese -- at ages 4 and 5 had 15 to 20 percent greater odds of having problems interacting with their peers, as reported by teachers, when they were 8 and 9.
There have been prior studies, making similar observations, about the psychological difficulties faced by obese children. But the question of whether obesity leads to unhappiness or social problems, or unhappiness and other mental health issues lead to obesity has left researchers perplexed.
"There have been a number of studies over the past 5 to 10 years looking at whether or not obesity in young children and adolescents is related to emotional, behavioral and mental health problems," noted Dr. Julie Lumeng, an assistant professor in the department of pediatrics and communicable diseases at University of Michigan C.S. Mott Children's Hospital. "There's been a lot of discussion about which direction that relationship goes in -- does obesity cause children to be unhappy, or is it that unhappy children are more likely to become obese? Many people think it goes in both ways."
Lumeng believes that obese children who are teased or ostracized - because they are overweight- are more likely to be unhappy or depressed.
Australia has a lower percentage of obese children than the United States. The Centers for Disease Control and Prevention puts pediatric obesity, in the U.S., at about 17 percent. That includes kids between the ages of 2-19. Australia's pediatric obesity rate is about 4.5 percent for boys and 5.3 percent for girls.
Those differences mean that the effect of obesity on a child's social functioning may be different in the United States than in Australia, Lumeng said.
The psychological effects of childhood obesity are not the only issues to be concerned about according to Dr. Jeffrey Schwimmer, a pediatric gastroenterologist and an associate professor of pediatrics at the University of California, San Diego.
He says that the physical health risks of obesity in childhood are also an important factor to consider. "Obesity at age 5 is a critical time point in life. It's the age at which most children are entering or in kindergarten, and children who are obese entering kindergarten and who remain obese over those first several years of elementary school are the most likely to end up with the health consequences we see,"
Obesity can lead to many types of health risks such as sleep apnea and fatty liver disease, which can, over time, cause irreversible damage to the liver, diabetes and high blood pressure. Heart disease, gallstones, asthma and menstrual problems are also associated with obesity in children and adults.
How can you help your overweight or obese child lose weight and be healthier? Begin by not singling out your child, but make the process a family lifestyle change.
To help prevent and treat obesity in your child the Mayo Clinic website offers these suggestions:
Start small. Gradual changes are easiest to incorporate into the daily routine -- and to maintain long term. Start by making a few small changes, such as turning off the TV during dinner, switching from soda to skim milk or water, and taking a family walk after dinner once a week.
Set goals. Set realistic, measurable goals for each family member, and then determine family goals. For example, your child's goal might be to eat fruit for afternoon snacks. Your goal might be to take a brisk walk three days a week. The family's goal might be to limit fast-food meals to once a month.
Recognize triggers. Be prepared for situations that may tempt you to fall back to your old habits. If you're used to eating popcorn at the movies, for example, bring only enough money for admission -- or agree that you'll share a small carton of popcorn with your child rather than ordering separate treats.
Celebrate success. Frequent rewards can help keep your family motivated. When your child meets a goal -- by asking for fruit rather than cookies after school, for example -- offer praise and attention. When your family meets a goal, brainstorm healthy ways to celebrate your success. You might try a family movie night, a weekend picnic or a trip to the pool.
Keep it positive. Focus on healthy lifestyle changes, rather than your child's appearance or a number on the scale. Remember, treating childhood obesity isn't a race. It takes time and dedication to replace established behaviors with new, healthier behaviors.
Be flexible. It'll take time to get used to your healthier habits. Encourage everyone to stick to the plan -- but if the goals aren't working for your family, consider making adjustments. It's better to create a new plan than to stick to one that isn't working.
Keep healthy foods on hand. Stock your kitchen with fruits, vegetables, whole-grains foods and other healthy choices. Keep junk food and sugary drinks out of the house.
Eat in. Reduce the number of meals your family eats in fast-food and other restaurants. Better yet, sit down together for family meals. Plan weekly menus using new recipes or healthier alternatives to family favorites. Keep portion sizes reasonable and allow seconds only on salad, fruits and vegetables. Encourage your kids to get involved in shopping and meal preparation.
Build physical activity into the daily routine. Put as much emphasis on moving more as on eating less. Organize family outings that involve physical activity, such as walking to the library or taking a family bike ride. Include children in active chores, such as washing the car or walking the dog. Encourage your kids to participate in school or community sports -- or to dance, jump rope or do other physical activities on their own.
Limit household screen time. Set reasonable rules for TV, computer and video game time, such as one to two hours a day for each family member -- including mom and dad. Keep TVs and computers out of the bedrooms, and don't allow eating in front of the TV or computer.
Parents have the most compelling and strongest effect on how their children view themselves and how they learn how to solve problems. Offer your child encouragement and praise, and most of all, lead by setting a good example.