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Fruits and Vegetables May Prolong Your Life

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Fruits and Vegetables May Prolong Your Life

Our Review Summary

Similar to another WebMD report we reviewed that was also about an article in the Archives of Internal Medicine, this one appears to be cribbed from the journal’s news release. The study reported that a one-time measurement of alpha-carotene blood levels showed that higher levels were associated with lower death rates recorded over the following 14 years. The story then leaps to the unfounded interpretation that the study results show eating foods rich in antioxidants fights disease. The story fails to point out that this sort of observational study cannot prove cause-and-effect.  (Read our primer on this topic.) And the story didn’t discuss any of the important limitations in the analysis. There are no independent sources quoted and the lack of that perspective makes it difficult for readers to understand how this study fits in with other evidence on nutrition and health.  

 

Why This Matters

“Eat your veggies” may appear to be a benign lead, but this sort of incomplete reporting can lead to potentially hazardous misinterpretations of the evidence on nutrition and health. Similar observational studies hinted at benefits of beta-carotene, but when beta-carotene supplements were tested in experiments, it turned out that not only were the pills not beneficial, but those taking the supplements actually had higher rates of lung cancer. Vitamin-E is another example of a food component that was wildly promoted by those who misinterpreted observational studies. Then many people were surprised when careful experiments failed to find the hoped-for health benefits. Careful reporting of the limitations and pitfalls of this sort of study is essential if readers are to get an accurate sense of what the evidence actually says… so they are less likely to be disappointed and discouraged in the future… and also less likely to be misled by those who have a financial interest in making claims that are not actually supported by the best evidence.

Criteria

Does the story adequately discuss the costs of the intervention?

Not Applicable

Not applicable. Costs weren’t discussed, but the costs of these common foods are well known.

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

Not Satisfactory

The story is simply wrong to state that the “study shows that eating foods rich in antioxidants, like vegetables and fruits, fights disease.” As noted above, this story does mention that  after similar studies pointing to health benefits of certain fruits and vegetables, follow-up studies have not shown that beta-carotene supplements reduce risks of dying from heart disease or cancer; nevertheless, the overall thrust of the story is that the study provides evidence of benefits… when the researchers actually limit themselves to saying the results are consistent with potential benefits and that they encourage further studies.

The story reports only the relative differences in death rates associated with one-time measurements of alpha-carotene blood levels, which is what the researchers and the news release highlighted. The actual numbers of deaths were in the article in the Archives of Internal Medicine, but they are hard to interpret, since they are not adjusted for age or other factors that were included in the analysis.

Does the story adequately explain/quantify the harms of the intervention?

Not Satisfactory

While it seems almost silly to worry about potential harms of eating more fruits and vegetables, the story does not include caveats that would help readers see how misinterpretation of the study results might cause harm. The story mentions that “studies have not shown that taking beta-carotene supplements reduces the risk of dying from heart disease or cancer.” It should have pointed out that an earlier round of observational studies of fruit and vegetable intake similar to this one produced rampant enthusiasm for beta-carotene, but then actual experiments had to be cut short because some participants taking the supplements had higher rates of lung cancer. Any story about potential benefits of specific components of foods should clearly remind readers that in some cases supplements containing these same components have been shown to be useless or even hazardous.

Does the story seem to grasp the quality of the evidence?

Not Satisfactory

The story lead inaccurately states that the study shows that eating food rich in antioxidants fights disease. Not only does the study not make that claim, this kind of observational study cannot prove cause-and-effect. Also, the story does not examine the claim that this study supports increasing consumption of these foods to prevent premature deaths, which is not accurate if taken to mean a cause-and-effect relationship.

The story does not address limitations of this study, including the concern that some other factor that was not included in the analysis might affect the results. For instance, other research indicates that people who have higher incomes or live in communities with higher incomes tend to live longer… and people in these neighborhoods also tend to eat a diet higher in fruits and vegetables… but this study did not include any data or adjustments for income or neighborhood.

The researchers noted in their article that “our results may be subject to residual confounding owing to unmeasured biomarkers or health behaviors.” The story should have addressed that important limitation.

Does the story commit disease-mongering?

Not Applicable

Not applicable, mainly because the story really didn’t give any background on any specific health problem or disease.

Does the story use independent sources and identify conflicts of interest?

Not Satisfactory

The story does not include comments from any independent sources. The lack of perspective deprives readers of the context needed to appreciate what this study says… and does not say. Since the researchers are employees of federal agencies, not associated with the supplement or food industries, and they reported no financial disclosure, it is of less concern that the story does not address potential conflicts of interest.

Does the story compare the new approach with existing alternatives?

Not Satisfactory

Other than saying that other studies failed to find benefits from beta-carotene supplements, the story fails to discuss what is known about how alpha-carotene might compare to other components of foods.

Does the story establish the availability of the treatment/test/product/procedure?

Satisfactory

The story lists a number of common foods that contain relatively high levels of alpha-carotene.

Does the story establish the true novelty of the approach?

Not Applicable

There is no claim of novelty in this story. However, the story fails to make clear how this study was different from other research on this topic.

Does the story appear to rely solely or largely on a news release?

Not Satisfactory

The story appears to be based on a news release from the Archives of Internal Medicine.  Entire sentences in the story appear to be lifted wholesale from the following news release.

“High Alpha-Carotene Levels Associated With Longer Life”
http://pubs.ama-assn.org/media/2010a/1122.dtl#1

Total Score: 1 of 7 Satisfactory

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