6th time I’ve called out BMJ news releases on observational studies

I do not enjoy this – repeatedly calling out The BMJ for its misleading news releases on observational studies.

But I’m going to keep doing it until I see a change.

The last time I did this, just two months ago, change was promised by The BMJ editor Trish Groves.

But here we go again.

The BMJ this week sent out the following news release.  I have highlighted the areas of concern in red.

Five daily portions of fruit and vegetables may be enough to lower risk of death

More than “five a day” appears to have no further effect, say researchers

Research: Fruit and vegetable consumption and mortality from all causes, cardiovascular disease, and cancer: systematic review and dose-response meta-analysis of prospective cohort studies

Eating five daily portions of fruit and vegetables is associated with a lower risk of death from any cause, particularly from cardiovascular disease, but beyond five portions appears to have no further effect, finds a study published on thebmj.com today.

These results conflict with a recent study published in BMJ’s Journal of Epidemiology and Community Health suggesting that seven or more daily portions of fruits and vegetables were linked to lowest risk of death.

There is growing evidence that increasing fruit and vegetable consumption is related to a lower risk of death from cardiovascular disease and cancer. However, the results are not entirely consistent.

So a team of researchers based in China and the United States decided to examine the association between fruit and vegetable intake and risk of all-cause, cardiovascular, and cancer deaths.

They analysed the results of sixteen studies involving a total of 833,234 participants and 56,423 deaths. Differences in study design and quality were taken into account to minimise bias. Higher consumption of fruit and vegetables was significantly associated with a lower risk of death from all causes, particularly from cardiovascular diseases.

Average risk of death from all causes was reduced by 5% for each additional daily serving of fruit and vegetables, while risk of cardiovascular death was reduced by 4% for each additional daily serving of fruit and vegetables.

But the researchers identified a threshold around five servings per day, after which the risk of death did not reduce further.

In contrast, higher consumption of fruit and vegetables was not appreciably associated with risk of death from cancer. The researchers suggest that, as well as advice to eat adequate amounts of fruit and vegetables, the adverse effects of obesity, physical inactivity, smoking and high alcohol intake on cancer risk should be further emphasised.

The researchers say their study “provides further evidence that a higher consumption of fruits and vegetables is associated with a lower risk of mortality from all causes, particularly from cardiovascular diseases. The results support current recommendations to increase consumption of fruits and vegetables to promote health and longevity.”

There’s a recurrent jumble of semantics in that release.

Sometimes it refers – appropriately – to “association.”  But in the 6 other areas highlighted, terms implying causation were used.

Yes, it was a huge systematic review and meta-analysis.  And yes, some may see it as supporting current recommendations to increase consumption of fruits and vegetables.”

But cause-and-effect was not established in this systematic review and meta-analysis.  Yet the term “effect” was used twice.  And if cause and effect haven’t been established, then neither can be risk be established.  Yet the term “risk” was used four times.

The last time I wrote about this, I called for 6 little words to be employed in The BMJ news releases:  “association does not necessarily imply causation.”

The BMJ editor Trish Groves wrote a comment in response to that piece, saying “Good idea.  We will, forthwith.”  I guess that forthwith hasn’t arrived yet.  Will it ever?

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