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It’s World Iron Awareness Week, so we decided to delve into some facts and figures on the topic.
This led us to a popular website, where the infographic statistics didn’t look quite right. One figure that really jumped out was: “8 in 10 toddlers don’t meet the recommended daily intake of iron”.
This statistic was cited from a study published in Public Health Nutrition - a reputable peer-reviewed journal.
In our fact checking effort (because we always do) the results were incorrectly reported. The reality was that '1 in 5 toddlers' were not meeting their iron requirements.
So Rachel lost her cool.
The first trigger. Improper use of dietary assessment cutoffs.
When evaluating hard earned dietay data from a study group, you should never, ever, ever, ever, ever, ever, ever use the recommended dietary intake (RDI).
Instead, the prevalence of nutrient inadequacy of a group should always be determined using the estimated average requirement (EAR).
Dietary Assessment 101
Ensuring you go back-to-the-basics is an important exercise throughout your career.
We spend about one-third - maybe even more - revisiting and reviewing the background knowledge before tackling more advanced content.
So let's take a step back. Every individual has their own unique dietary requirements. This is NOT a 'one size fits all' approach. When sampling a study population, the evidence has shown that requirements are normal distributed - meaning a handful people have very low and very high requirements and then most fall in between.
The RDI is the “average daily intake of a nutrient sufficient to meet the requirements of nearly all (97-98%) healthy individuals in a particular life stage and sex group” – meaning it exceeds the requirements of most people in a particular group.
The wrong move. With this definition in mind, to report that the percentage of individuals with a usual intake below the RDI as not achieving their nutrient requirement defies science and grossly overestimates the prevalence of inadequacy.
Incorrect use of the RDI in the published paper resulted in finding that '8 of 10 toddlers were not achieving their iron requirements.
The right move. On the other hand, the EAR is the “daily nutrient level estimated to meet the requirements of half the healthy individuals within a particular life stage and sex group”.
If an individual’s usual intake is at the EAR there is a 50% probability their intake is adequate.
When examining a whole group of individuals in a study, it has been shown statistically that the percent of people consuming intakes below the EAR is indeed a really good estimate of the true prevalence of inadequacy.
So with the correct approach, use of the EAR in the published study resulted in '1 in 5' toddlers who are not reaching their required iron intakes. This is a substantial change from 80% - a severe public health issue - to the more accurate report of 20% inadequacy.
Taking a closer look at the paper cited on the iron awareness website, the authors wrongly report that among children aged 6-23 months only 22% achieved the RDI (this is where the “8 in 10” statistic comes from).
Fortunately, the authors did estimate the percentage of infants and toddlers consuming less than the EAR. This equated to 25% – so 1 in 4. Breaking down these results even further into age group categories: 6-11 months and 12-23 months, the prevalence of inadequate intakes was 41% and 19%, respectively.
Toddlers are aged 1-2 years and so the website should report 1 in 5 toddlers are consuming inadequate amounts of iron – quite different from the 8 in 10 reported. We will send them our newsletter ;)
The second trigger. Reporting the mean intake against the EAR
We want to also highlight another common yet incorrect report of dietary data in published research studies. Many researchers do not even examine the distribution of participant intakes. Rather they report only the mean intake of the study group and compare it against the EAR - or god forbid, the RDI. If the mean of the group is less than the selected cutpoint - they report that participants did not achieve recommended intakes. This is like dynamite for Rachel!
Oh we're not finished... it is also very important to note that dietary data should be statistically adjusted to better reflect usual intake before calculating the prevalence of inadequacy.
What we eat differs from day to day and so we need to account for this variation in our intake.
To do so, studies need more than one day of intake - at least from a subsample of the group. This information can then used to make a statistical adjustment which narrows the distribution of intakes making a more reliable estimate.
Unfortunately, the study on toddlers did NOT make these adjustments even though two days of dietary intake was collected.
By not adjusting, the distribution of intakes is wider and the prevalence of inadequacy (i.e., percentage of children consuming less that the EAR) is likely to be over-estimated (see figure above). Meaning the correct number of toddlers consuming inadequate iron intakes is likely even less than 1 in 5.
This is a good reminder to go to the data source, especially if something looks off.
The science of dietary assessment and its complexities are often undervalued. Wrongly interpreting this data leads to wildly flawed conclusions resulting in needless interventions that waste both time and limited resources.
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