About 12 percent of women who give birth are smokers, and many of them continue to smoke as their babies grow. For infants, exposure to tobacco smoke can have enormous health consequences. Researchers from Brown University and the Harvard School of Public Health looked at the link between smoking and infant colic, which is excessive crying that might be caused by intestinal discomfort.

What the researchers wanted to know: Are babies who are regularly exposed to tobacco smoke more likely to develop colic?

What they did: This paper was a meta-analysis, meaning that the researchers did not do a new study but instead examined other studies that have been done over the past several years to see if they could draw any conclusions. They looked at literature that examined how often mothers who smoke have colicky babies as well as literature that examined the changes in a baby's body due to smoke and how that might affect the baby.

What they found: Current studies seem to support a link between smoke exposure and colicky babies. Moms who smoked were more likely to have babies that cried a lot and developed colic. Studies have shown that smoke exposure increases a compound in infant's intestines that, when present in high levels, can cause colic.

What it means to you: Add colic to the list of children's health problems that can result from tobacco smoke exposure. One study found that 40 percent of children under the age of 5 live with someone who smokes, so it is still a major health concern. Colic causes added stress on new parents and makes for distressing days and sleepless nights. For women who are pregnant or have just had a baby, the message remains the same: The earlier you quit, the better.

Caveats: Like all meta-analyses, this study could be biased because it reviews studies that have already been published, which are probably more likely to show a link between smoking and colic. (Those that showed no link are less likely to have been published.)

Find out more: The Centers for Disease Control and Prevention has a webpage with basic facts about children's exposure to smoking and its consequences.

The U.S. surgeon general's website has tips for pregnant women who want to quit smoking, which you can print out and personalize with your own personal plan.

Read the article: Shenassa, E.D. and M. Brown. "Maternal Smoking And Infantile Gastrointestinal Dysregulation: The Case of Colic." Pediatrics. October 2004, Vol. 114, No. 4, pp. e497–e505.

Abstract online: http://pediatrics.aappublications.org