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Researchers found that was the case regardless of how much total food teenagers ate or how often they drank sugary beverages.
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Dietary sodium has been linked to obesity in previous studies. But most scientists believe it's only an indirect association, because people who consume a lot of sodium tend to eat more food in general. "Our study and studies looking into national data all show that average dietary sodium consumed is 3 300 - 3 400 milligrams daily in children, as high as that of adults," Dr Haidong Zhu told Reuters Health in an e-mail. She led the new study at Georgia Regents University in Augusta.
Less than 1 500 mg per day
The American Heart Association recommends that everyone keep sodium intake to less than 1 500 mg per day, but 90% of children exceed that amount, Zhu noted.
For their study, she and her colleagues measured the body composition of 766 healthy 14- to 18-year-olds. About half of the teens were African American and the other half were white.
The researchers also collected diet information from the participants by asking them to remember everything they had eaten in the past 24 hours up to seven different times over a few months. On average, the teens consumed about 3 280 mg of sodium every day.
Kids who ate more sodium tended to be heavier. Those in the top third of sodium intake weighed approximately 1.4 kg more than those in the bottom third, on average – about 67 kg versus 65 kg.
Teens with a high-sodium diet also generally had a higher percentage of body fat and showed more signs of body-wide inflammation.
Bigger fat cells
Those associations held up when the researchers took into account teens' physical activity levels as well as how much food they ate and how many sugar-sweetened beverages they drank, according to the findings published in Paediatrics.
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Although the study links sodium intake to inflammation and weight regardless of calories and soft drink consumption, Zhu said, it doesn't explain why. "Animal studies suggest that diets high in salt promote fat cells to grow bigger," Zhu said.
She added that high-salt diets might stimulate the brain's reward and pleasure centre, which increases the chance of overeating and obesity. "More research in humans is needed," Zhu said. "This study suggests that limiting sodium intake will help reduce obesity – we already know that limiting sodium intake helps reduce high blood pressure," Dr Elliott Antman told Reuters Health in an email. "It reinforces the fact that our population – children and adults – consumes too much sodium in the course of a day," he added.
Antman is a cardiologist at Brigham and Women's Hospital in Boston and president-elect of the American Heart Association. He was not involved in the new study.
Use spices rather than salt
He commended the authors for enrolling a large number of African-American adolescents. African Americans tend to have higher risk of obesity, type 2 diabetes and high blood pressure than the general population.
Antman advised parents to be careful about how much sodium their children are getting. "Taste preferences for salt appear to be formed early in life. Therefore, parents should worry about their kids' sodium intake since healthy dietary habits learned in childhood are carried forward to adulthood," he said.
Parents should read nutrition labels at the supermarket to shop wisely for the foods they feed their children, Antman added. "Parents should also emphasize eating at home rather than eating at restaurants or fast food chains. Using spices rather than salt may help reduce the amount sodium their children eat," he said.
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Zhu noted that more than 75% of consumed sodium comes from processed foods and fast food. "This is why establishing a healthy food habit in early childhood is so important," she said. "People should eat less processed foods (and) fast food and eat more fresh fruit and vegetables."
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