New research suggests that drinking lots of artificially sweetened beverages may be linked with an increased risk of premature births.

“It may be non-optional for pregnant women to have high consumption of these types of products,” Dr. Thorhallur I. Halldorsson of the Statens Serum Institut in Copenhagen, one of the researchers on the study, told Reuters Health.

“Diet” drinks are widely promoted as a healthy alternative to sugary sodas and juices, but Halldorsson and his colleagues note that there’s been little research on the safety of regular consumption of artificial sweeteners in humans.

Soft drinks - both artificially sweetened and sugar sweetened - were recently linked to high blood pressure, the researchers add, which increases the risk of premature delivery. To investigate whether there might be a direct link, the researchers looked at nearly 60,000 Danish women who reported on their diet, including how many soft drinks they had each day, at around 25 weeks of pregnancy.

Around 5 percent of women delivered their babies before 37 weeks.

Women who had at least one serving of artificially sweetened soda a day while they were pregnant were 38 percent more likely to deliver preterm than women who drank no diet soda at all, the researchers report in the American Journal of Clinical Nutrition.

Women who had at least four diet sodas a day were nearly 80 percent more likely to deliver preterm. The association was the same for normal-weight and overweight women.

The researchers did not report the actual risk of premature babies in each group. However, according to the March of Dimes, one in eight babies - or around 13 percent - is born too soon. This means that if drinking diet soda does indeed increase risk - which must first be confirmed by other research teams - a woman who drank at least one diet soda daily would have a 17 percent risk, while her risk would be around 22 percent if she drank four or more diet sodas.

In a statement, the Calorie Control Council, a lobbying group for companies that make and distribute low-calorie foods, called the study “misleading.”

“This study may unduly alarm pregnant women. While this study is counter to the weight of the scientific evidence demonstrating that low-calorie sweeteners are safe for use in pregnancy, research has shown that overweight and obesity can negatively affect pregnancy outcomes,” Beth Hubrich, a dietitian with the council, said in the statement. “Further, low-calorie sweeteners can help pregnant women enjoy the taste of sweets without excess calories, leaving room for nutritious foods and beverages without excess weight gain - something that has been shown to be harmful to both the mother and developing baby.”

Because only diet soda was linked to preterm delivery, not sugar-sweetened soda, the findings suggest that the artificial sweetener itself, not soda drinking, could account for the relationship, the researchers say. However, they add, other possible causes for the link can’t be ruled out.

The researchers didn’t look at specific artificial sweeteners, and Halldorsson noted that many beverages contain more than one of these chemicals. However, he and his colleagues say, there is indirect evidence linking the sweetener aspartame to preterm delivery in animals.

Aspartame breaks down into methanol and other substances in the body, which can in turn be converted to toxic substances such as formaldehyde and formic acid, the researchers explain. And studies in non-human primates have linked even very low exposure to methanol to shortened pregnancy and labor complications.

While pregnant women who consume soft drinks shouldn’t be alarmed by the findings, Halldorsson said, “what we are seeing warrants further attention.”

According to the American College of Obstetricians and Gynecologists, women who normally use the artificial sweeteners saccharin (Sweet n’ Low), aspartame (NutraSweet), sucralose (Splenda) or acesulfame K (Sunett, Sweet One) can safely continue to do so “in moderation” during pregnancy.

SOURCE:  American Journal of Clinical Nutrition, online June 30, 2010.