Diet Soda Linked to Preterm Birth

A new study suggests that pregnant moms may want to put down the diet sodas.

September 27, 2010

Water is the healthiest beverage if you're expecting (and if you're not).

RODALE NEWS, EMMAUS, PA—In the United States, one out of every eight babies is born prematurely, according to the March of Dimes. It's not clear why preterm births are so common, but it could have something to do with pesticide exposures, stress, and rising obesity levels, the organization suggests. So it would stand to reason that doing things to counteract stress and obesity, like, say, drinking diet soda, might help. But a new study published in the American Journal of Clinical Nutrition suggests that diet soft drinks may make the problem worse. Researchers from Denmark found that women who drink diet sodas are at an even higher risk for delivering babies prematurely than women who drink full-calorie sodas.

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THE DETAILS: Information was collected from 59,334 pregnant women participating in an ongoing Danish study. Diet soda intake was assessed using food frequency questionnaires, and government registries provided information on dates of birth, which were used to determine births that occurred at less than 37 weeks. After accounting for other factors that might affect preterm deliveries, such as smoking during pregnancy and the age and weight of the mother, the authors found that women who drank an artificially sweetened carbonated soda once per day were 38 percent more likely to have a preterm delivery than women who drank no diet sodas at all. There was a similar increase in risk for drinking noncarbonated artificially sweetened drinks, but the risk wasn't quite as significant. The authors also found no increase in risk among women who drank sugar-sweetened carbonated and noncarbonated soft drinks.

WHAT IT MEANS: The fact that the authors saw an increase in risk with diet carbonated sodas and not with regular sodas or noncarbonated diet drinks suggests that artificial sweeteners used in sodas, such as aspartame and acesulfame-K (both commonly used in Danish and American sodas) could be to blame. "The type and mixture of sweeteners used in non-carbonated soft drinks is considerably different compared to those used in carbonated soft drinks, at least on the Danish market," says Thorhallur Ingi Halldorsson, PhD, senior scientist at the Statens Serum Institut in Copenhagen and lead author of the study. In addition, she cites a 2005 analysis finding that the amount of artificial sweeteners used in carbonated diet sodas is two to three times higher than the amounts used in non-carbonated diet sodas.

Part of the problem could be attributed to what happens once artificial sweeteners enter the body. Aspartame, for instance, breaks down into aspartic acid, phenylalanine, and methanol after ingestion; animal studies suggest that methanol in the blood can shorten pregnancies and lead to other delivery complications for the mother.

Halldorsson is hesitant to pin all the blame on artificial sweeteners, she says. "There are, of course, other alternative explanations including that this might be due to some lifestyle or other unidentified confounders," she notes. But, she adds, "pregnant women are encouraged to eat healthy foods during pregnancy, and frequent daily intake of soft drinks is not particularly healthy."

While nothing beats good old water, in terms of healthy drinks, here are a few beverages that are better choices than diet drinks or oversweetened sodas:

• Red raspberry leaf tea. Available as loose leaves in your local health-food store, red raspberry leaf tones your uterus and helps relax muscles, making your delivery easier, and it has anti-inflammatory properties. Steep ½ cup of leaves in a quart of hot water to make a tea, then strain it. Drink one cup a day in the first trimester, two during your second, and three during your third, recommends Julie McKee, MD, distinguished professor of medicine at The University of Texas Medical Branch in Galveston. You can even refrigerate the tea if you prefer it iced.

• Green tea. There's a great deal of controversy surrounding the issue of drinking caffeine during pregnancy. Research as to whether it can harm the baby or lead to preterm labor is often conflicting, and a meta-analysis of 22 studies from the past three decades, just published in the American Journal of Clinical Nutrition, found no association between caffeine intake and risk of preterm birth. So talk to your obstetrician about whether drinking caffeine is a good idea for you. If it's OK, and you're craving a little pick-me-up, opt for green tea, which has the lowest levels of caffeine of all non-herbal teas. Or, go for something like Steaz Zero Calorie Sparkling Green Tea. It's sweetened with erythritol, a zero-calorie natural sweetener, and contains about 15 milligrams of caffeine per bottle (compared with 40 to 50 milligrams for other non-herbal teas). Plus, it contains folic acid, a vital nutrient for mothers-to-be.

• Smoothies. One downside to diet sodas, as Halldorsson points out, is that they provide very little nutritional value, and you don't want to fill up on non-nutritional foods while pregnant. Making smoothies with milk, yogurt, fruits, and even peanut butter is a healthy way to satisfy a sweet tooth while also bulking up on calcium, protein, folic acid, vitamin C, and energy-boosting (good) carbohydrates. Find tons of tasty smoothie recipes with the Rodale Recipe Finder.