Fascinating information from Ole Bjørn Rekdal in a paper on academic urban legends:
“The following quote, including the reference, is taken from an article published by K. Sune Larsson in the Journal of Internal Medicine:
The myth from the 1930s that spinach is a rich source of iron was due to misleading information in the original publication: a malpositioned decimal point gave a 10-fold overestimate of iron content [Hamblin, 1981]. (Larsson, 1995: 448–449)1
The quote caught my attention for two reasons. First, it falsified an idea that I had carried with me since I was a child, that spinach is an excellent source of iron. The most striking
thing, however, was that a single decimal point, misplaced 80 years ago, had affected not just myself and my now deceased parents, but also a large number of others in what we place on our table.”
and
“Truth be told, there is iron in spinach, but not significantly more than in other green vegetables, and few people can consume spinach in large quantities. A larger problem
with the idea of spinach as a good source of iron, however, is that it also contains substances that strongly inhibit the intestinal absorption of iron (see e.g. Garrison, 2009:
400). Simply put, spinach should not at all be the first food choice of those suffering from iron deficiency.
Larsson’s article made me aware of the remarkable fact that a large number of people in the Western world have been misled for a staggeringly long time. Since so many people
still believe that spinach is a good source of iron, I have good reason to convey this newfound knowledge to others. The story of this decimal point error is, in addition, a brilliant illustration of how a small stroke may fell a great oak, and a reminder of the importance of accuracy and quality control in the production and distribution of scientific knowledge.”
Rekdal goes on to show the assertion that that spinach-is-high-in-iron belief is a more complicated story that may involve more than a decimal issue, and he reveals the challenge in tracking down the original source of that claim.
He exposes an even bigger irony, as revealed through another quote:
“The story that the iron content of spinach was a myth based on a misplaced decimal point is itself a myth. Spinach has a lot of iron, just like other green vegetables, but it is unavailable for absorption.
I should know, I was the one who was responsible for propagating the myth in a BMJ article.”
and
“Now some fascinating research by Mike Sutton has found out the whole truth behind the decimal point and the iron in spinach myth and I am pleased to be able to say that I was right about spinach being useless as a source of iron, but utterly wrong about why the myth has taken hold. … The moral of this story is that a good story is not necessarily a true story. (Hamblin, 2010)”