August 15, 2018

Milled Maize Causes Cancer – Not Yet

A Kenkey meal prepared from milled maize. Credit: Myjoyonline

Earlier this week a number of news outlets carried a story with the headline “Scientists alarmed at cancer causing metal particles in milled maize”. Suggesting that milled maize causes cancer, this is of great concern because milled maize forms the basis of staple diets such as banku and kenkey which are enjoyed in different forms across African countries. Living in the centre of Accra and being a Ga myself, not a week goes by without a few balls of kenkey finding its way onto my plate. It stands to reason that I took a personal interest in the story and to determine for myself how much truth there was in the news headline.

The news story that was published by leading media houses fanned conversations about how milled maize causes cancer.  No media house referenced the original research publication or the researchers at KNUST who performed the work so this made it difficult to find the original source (that’s a conversation for another day). However I turned to the Ghana STEM Network for assistance to track down the original source of the research and here is what I found.

What was the story?

The story is based on a 2011 research publication titled “The quality of locally manufactured corn-mill grinding plates” and published in the Journal of Science of Technology by S. Kwofie, A. Andrews and E. Mensah at the departments of Materials Engineering and Agricultural Engineering of KNUST. Two things immediately worth noting; firstly the Journal of Science and Technology has what is called a very low impact factor. Think of it as a high school newspaper in comparison to a national newspaper such as the Daily Graphic. What this means is that although what is published there may be true, the standards of quality are very low and the information doesn’t really inform the decision making of anyone that matters. Secondly the focus of the publication was on the quality of the mill grinding plates, the idea that milled maize causes cancer was nothing more than a foot note insinuation.

However, regardless of who published it and where they published it, the real question is “Did the researchers find information which can infer that milled maize causes cancer?”.

What did the researchers do?

Allow me to summarise their work for you. The research used brand new locally manufactured milling plates for 36 days during which a total of 1800kg of both dry and wet maize was processed. A sample of the maize milled each day was analysed for iron content and compared with the iron content of an equal sample of un-milled (crushed) maize. The iron in the amuont of maize milled every 3 days ranged from 4 – 355g for dry maize and 0.3 – 57g for wet maize. Based on numbers they provide that the average Ghanaian eats 500 – 1000g of milled maize a day, means that if you use dry mailed maize you are eating 49 – 97mg of iron and 25 – 50 mg if you use wet milled maize.  

A locally manufactured corn-mill plate. Kwofie et al 2011

According to the World Health Organisation, recommended daily iron intake ranges from 8-18 mg a day. Depending on pregnancy, breastfeeding and menstruation, females are advised to significantly exceed this range up to 27mg. The most amount of iron your body can safely deal with is around 45mg a day. So clearly what the researchers report that the average Ghanaian is consuming 25-97mg (depending on dry or wet milled maize) of iron from maize products alone is a reason for concern. This is not counting the iron in take from red meat and other sources.

Should I panic?

Before you start panicking and tell your whole community that milled maize causes cancer, you might want to consider reading further. Analysing the publication revealed some errors on the part of the researchers which could mean that their conclusions are wrong.

The researchers used new milling plates for 36 days and confirm that the plates grew too dull to be effective. It is the wearing of the plates which contaminates the milled maize with iron. We also have no information how sharpening of the plates which happens in normal mills affects wearing. Afterall, I doubt there is any mill owner out there who changes their plates every 36 days.

The data the researchers present suggests that between the first three days and the last three days that the plates were used, the iron content decreased by 35% in dry maize and 88% in wet maize. Does this mean older plates contaminate the maize with less iron?

Although the researchers collected daily samples of milled maize to measure the amount of iron in it, they only show us the average iron for every three days. I have been around enough researchers to know that this is done to hide “variation” and results that will otherwise not make sense. For example, if I measure 12mg iron on day 1, 1mg on day 2 and 5mg on day 3, I can get the average of these three numbers as 6mg and tell you that between day1-3, I measured 6mg of iron. If I showed you the real number for each day (12mg, 1mg and 5mg) you will clearly see that not only did the numbers decrease over time but they also seemed to go down and up – maybe randomly. I cannot trust the conclusions of any researcher who presents their numbers like this. This is what I mean about standards, the difference between a high school newspaper and a national newspaper.  

Last but not least is something that I believe everyone can identify with. The researchers state that:

“For a total mass of 1800 kg of maize milled, the amount of iron metal particles measured was about 175 kg and 90 kg for ‘dry’ and ‘wet’ milling, respectively.”

Think about that for a minute. This means that 5-10% of your banku, kenkey, akple and maize porridge is made up of metal – iron – dade! Iron tastes a bit like blood and I don’t know about you but I think I will be able to tell if 10% of my kenkey tastes like blood.     

It is known that too much iron increases the risk of cancer, heart disease and diabetes. However based on the research which forms the basis of the headlines spoken of here, I am not convinced that the low quality grinding plates used at some mills leads to the levels of excess iron in milled maize which can lead to cancer.  The proposal to re-engineer the composition of the milling plates is commendable and should be the focus of the news headlines without the cancer scares. You are going to need stronger evidence to take away balls of kenkey from my plate.

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