Gut health study recalled after zinc levels in tuna miscalculated

02-May-2018 - Last updated on 01-May-2018 at 11:35 GMT

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Research that looked into the effect of elevated zinc levels in canned tuna on gut health has had to be re-examined after the journal retracted the study due to 'unreliable data' featured in the paper.

The study, which tested whether mineral levels found in canned tuna was contributing to nutrient absorption issues, was subject to recall earlier this month by the Food & Function’s executive editor Philippa Hughes.

“The following article ‘ZnO nanoparticles affect intestinal function in an in vitro model,” by Fabiola Moreno-Olivas, Elad Tako and Gretchen Mahler has been published in Food & Function,” the expression of concern said.

“The article reports that the amount of zinc present in canned food is above the recommended dietary allowance.

“The Royal Society of Chemistry has been contacted by the authors to inform us that the data within the paper is not reliable.

“Food & Function is publishing this expression of concern to alert readers. An investigation is underway, and this notice will be updated when a final outcome is reached.”

Tuna and asparagus

Researchers from Binghamton University and the Department of Agriculture, in the US, reported zinc levels in a meal containing a typical tuna portion and an asparagus portion to be 996 milligrams (mg).

The figure is 100 times the recommended daily intake as the team went on to reveal that exposing cells to this amount of zinc led to a 75% decrease in iron absorption and a 30% decrease in glucose absorption.

This amount of zinc also resulted in a reduction of the surface area of the cells, so there was less surface area available to absorb nutrients.

NHS Choices, the official website of the National Health Service in England, calculated that there should have been 2.1mg of zinc in the meal containing a portion of tuna and a portion of asparagus.

Speaking to Retraction Watch, one of the authors of the paper Dr Gretchen Mahler, associate professor and graduate program director of Binghamton University, said that, “We heard back from a lot of people very quickly that there was a mistake”.

“We responded to everyone and never tried to cover up the mistake or anything. We let the publisher know as soon as we figured out that there was an error.

We are sorry, and I am embarrassed that there was such a stupid mistake in our calculations, but in the end it is good that we know and that people are checking facts before they publish.”

Overt toxicity not seen

News of the retraction came too late for a number of UK news publications such as The Sun and The Daily Mail, which reported the incorrect amount of zinc could be causing digestion problems.

However, Dr Mahler added that the zinc, even in such high doses, did not have a large effect on gut function.

“We didn’t see overt toxicity, like cell death, even at the highest doses studied,” she explained.

“The more subtle effects that we did see, like changes in glucose absorption, were present at the low dose.”

Back in 2000, the Food Standard Agency's UK Total Diet Study, took a look at levels of several metal elements (including zinc) contained in foods and supplements, and whether they presented a health risk to humans. The study concluded that dietary levels of zinc posed no such risk.

The European Food and Safety Agency’s (EFSA) average requirements (ARs) for zinc range from 6.2 to 10.2 mg/day for women with a reference weight of 58.5 kg and from 7.5 to 12.7 mg/day for men with a reference weight of 68.1 kg.