A survey found that by 2008, 12.5% of children were drinking artificially-sweetened beverages, up from 6% a decade earlier.

The researchers also found that a quarter of the Americans surveyed in 2007 and 2008 had a diet drink in the past day, versus just 19% in 1999 and 2000.

Senior researcher Dr. Miriam B. Vos, of Emory University in Atlanta said the size of the increase among kids was unexpected.

“We do want children to drink less sugar,” Vos told Reuters. “But the challenge is that there are no studies that have looked at the long-term health effects of artificial sweeteners in growing children.”

She said animal research has raised some potential concerns about drinking drinks which contain artificial sweeteners. Animals in a study fed with artificial sweeteners have shown weight gain, suggesting there could be some effect on metabolism.

Vos said large population studies have not shown diet-beverage drinkers are doing better weight-wise than those who drink regular sugared soft drinks, and they tend to weigh more than people who favor water.

The findings are based on more than 42,000 Americans who took part in a periodic federal health survey.

Studies also show that diet-beverage drinkers have an increased risk of diabetes, heart problems and stroke.

Vos said she recommends that kids stick with water and milk, which provides protein, calcium and other nutrients.