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Is vitamin C a remedy for smoking during pregnancy? Too soon to tell based on preliminary study

Vitamin C May Reduce Harm to Infants’ Lungs Caused by Smoking During Pregnancy

Our Review Summary

The news release highlights a randomized, controlled study of 251 women who smoked during pregnancy with this research question: will vitamin C supplementation improve the pulmonary function tests of the infants?

Unfortunately, the news release doesn’t make it clear that the study did not meet its primary endpoint. Related lung function tests did show improvement but the significance of these results is not made clear, and no supporting data is included.

One thing that is included, and we were very happy to see, is that regardless of the results of this study, the lead author points out:

“Helping mothers quit smoking should remain the primary goal for health professionals.”


Why This Matters

Despite well known health risks, some women continue to smoke during pregnancy. The release quotes the study’s lead author making a compelling argument that finding a “safe and inexpensive intervention” to protect the babies of mothers who continue to smoke during pregnancy would be a major public health advance.

But this news release touts preliminary results that may not be ready for prime time, and certainly don’t justify an enticing headline suggesting this experimental approach may be ready for use to protect the babies of smoking mothers.

It’s also a classic example of why results based on physiologic markers — in this case a very specific lung test in newborns — must be interpreted with caution, and not interpreted as synonymous with meaningful long term clinical outcomes.


Does the news release adequately discuss the costs of the intervention?

Not Applicable

Cost of vitamin C supplementation is not mentioned.  Most people are aware that vitamin C is relatively inexpensive.

According to Walmart, CVS, and Amazon, a 100-day supply of 500 mg vitamin C tablets costs roughly $5.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

From the release:

“Infants whose mothers took 500 milligrams of Vitamin C (in addition to their prenatal vitamin) had significantly better forced expiratory flows (FEFs).”

We’re told FEFs measure how fast air can be exhaled from the lungs and are an important measure of lung function (because they can detect airway obstruction).

However, no data are provided in the release to show readers just how significant the improved flows are. This information is in the study and should have been described in the release, too. The study states that changes of half this size are predictive of clinical respiratory disease later in childhood.

Does the news release adequately explain/quantify the harms of the intervention?

Not Satisfactory

The release doesn’t mention any potential harms from vitamin C use. Since some readers may take license with these preliminary findings — and think more vitamin C is better (ie. improve their infant’s lung function) — the potential harms of vitamin C should have been included.

People can have allergic reactions to vitamin C at even low doses. At higher doses it can be problematic in people with kidney disease, and could be detrimental to fetuses.

Does the news release seem to grasp the quality of the evidence?

Not Satisfactory

This study only examined changes in very specific pulmonary function tests of 3-month-olds whose tobacco-smoking mothers did/didn’t take vitamin C during pregnancy.

In fact, the primary endpoint (FEF-75) did not improve with vitamin C supplementation, but other lung test parameters did. Unfortunately, the news release does not clarify the significance of this for readers. Rather it’s implied — most notably in the headline — that these improved lung test results suggest vitamin C reduced lung damage from maternal smoking.

This small study can not demonstrate that. These lung tests measure current lung function, but that does not mean they can be assumed to directly reflect future lung health. The research can’t yet tell us that vitamin c use in pregnancy will result in any changes in lung health later on.

Does the news release commit disease-mongering?

Not Applicable

The news release doesn’t engage in disease mongering — there’s a recognized association between smoke exposure and adverse health effects in children. But nor does it give us any idea of the scope of the problem. According to the Centers for Disease Control and Prevention (CDC), about 10% of expectant mothers surveyed said they smoked during the last 3 months of their pregnancy.

Does the news release identify funding sources & disclose conflicts of interest?


Funding is very clearly attributed to the National Heart, Lung, and Blood Institute and the Office of Dietary Supplements.

Conflicts of interest are not mentioned, and none were found.


Does the news release compare the new approach with existing alternatives?


We were glad to see this important caveat relating to an alternative intervention included:

“Helping mothers quit smoking should remain the primary goal for health professionals and public health officials.”

Does the news release establish the availability of the treatment/test/product/procedure?

Not Applicable

The release doesn’t address availability but it can be safely presumed that readers know vitamin C supplements are widely available.

Does the news release establish the true novelty of the approach?


The news release makes it clear the authors of this study have done previous research in this area, are trying to find more accurate ways to assess lung function in infants, and will continue to follow the infants in this study to assess their lung function over the long-term.

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?

Not Satisfactory

Even with the use of “may,” the headline is unjustified because it presumes the surrogate marker (lung function test) used in this study accurately reflects future lung health.

In other words, improvements of unknown future significance in some lung tests in the infants whose mothers took vitamin C does not justify implications that vitamin C is going to be protective.

Total Score: 3 of 7 Satisfactory


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