TUESDAY, Jan. 18, 2005 (HealthDayNews) -- In a new study that seems to raise more questions than it answers, Scottish researchers report that a high intake of vitamin C during pregnancy might raise the risk of an infant developing wheezing problems as a toddler.
The researchers themselves stress that the finding is "spurious," and one expert suggests the study shouldn't change the eating habits of expectant mothers.
The researchers did stand by their finding that a low dietary intake of vitamin E during pregnancy is associated with an increased likelihood of wheezing in the second year of life and of an increase in eczema in children born to allergic mothers.
But the shock came when they looked at vitamin C intake.
"Much to our surprise and consternation, we also demonstrated that a high maternal intake of vitamin C was associated with increased wheeze in the second year of life," said researcher Dr. Graham Devereux, a consultant respiratory physician at the Aberdeen Royal Infirmary.
"We strongly suspect that this association is spurious; it contradicts all previous work. We have not demonstrated an association between vitamin C and infant immune responses," Devereux said.
"We feel that the main result of this study relates to vitamin E, and we are confident in our vitamin E findings," Devereux said. "We feel that the vitamin C association is most likely to be spurious and is not the main focus of the study, and should not be highlighted to the detriment of the vitamin E associations."
Devereux did say that high vitamin C intake is a marker for higher socioeconomic status and a health-conscious lifestyle, which are factors known to be associated with increased asthma and allergy. "It is possible, but seems unlikely, that the vitamin C association may be real. The consumption of vitamin C-rich fruit juices has certainly increased in recent years," he added.
The report appears in the Jan. 14 issue of the American Journal of Respiratory and Critical Care Medicine.
In their study, Devereux's team collected data on 1,300 mothers and their children. The mothers were asked to complete a 145-item food frequency questionnaire that dealt with their diet during pregnancy. The mothers also took a scratch test for allergies, had their blood antioxidant levels measured, and completed follow-up health questionnaires when their children were 6, 12 and 24 months of age.
The researchers found that higher vitamin E intake during pregnancy was associated with fewer cases of wheeze in the absence of a cold. And in children whose mothers had an inherited tendency to allergies, high vitamin E intake was associated with fewer cases of childhood eczema.
Devereux explained that food frequency questionnaires are not good at quantifying an individual's absolute intake, although they are good at ranking intakes within a given population. So, there was not a specific threshold at which either vitamin began to show an effect.
However, Devereux added, "We have no reasons to suspect that the intakes of these women were any different to the general population from which they were drawn."
The results do suggest that a mother's diet during pregnancy may influence the development of respiratory problems and eczema in the second year of life, Devereux said.
"However, these results are preliminary and need to be reproduced by further studies. Although, in the future, it may be possible to reduce the risk of childhood asthma and allergy by modifying maternal diet during pregnancy, at the present time pregnant women should not change their diet during pregnancy," he advised.
One expert is not swayed by the latest findings.
"The associations between vitamin E, vitamin C and asthma are weak, and are as likely statistical flukes as not," said Dr. David L. Katz, director of the Prevention Research Center at Yale University School of Medicine.
"The strength of the associations and the study methodology fail to persuade me that these associations have any public health significance. The only real implication here is that better-controlled studies of these associations are warranted before any pertinent recommendations to the public are made," Katz added.
The U.S. Centers for Disease Control and Prevention can tell you more about asthma.