The nutrients I've covered so far in this series all have the potential to be too low
on a plant-based diet, but recently I had a query about manganese, with which we have
the opposite problem - it can be too high.
In fact, deficiency of this essential trace element is uncommon and is not a problem with
almost any kind of diet.
But like we saw with phytate in my video on zinc, manganese can be thought of as a marker
of healthy diets given that it is found mostly in plants and so can approach the tolerable
upper intake level in diets rich in plant matter, and it is actually quite easy to exceed
this upper limit.
The question is, how much of a problem is this?
Well first of all, why must there be an upper limit set at all?
Other nutrients like chromium, vitamin K and certain B vitamins have no defined tolerable
upper intake level, so what's so bad about manganese?
We know that high levels are in fact dangerous primarily from cases of occupational inhalation
of manganese dust and also drinking manganese-contaminated water, which can result in the permanent neurolgical
disorder known as manganism, characterised by Parkinson's-like symptoms.
So it has been established that we do indeed need to define an intake level above which
we should not go to prevent these adverse health consequences.
Unfortunately, an actual threshold level that would result in pathology has not been established,
so the best we have to go on is observation of populations that do not have any health
consequences of excess, and what their level of intake is.
Following a conservative approach, the National Academy of Medicine has set this upper limit
at 11 mg per day for all adults based on data presented by Dr. Greger - no, not the one
you're thinking of!
JL Greger presented data indicating that people eating Western-type and vegetarian diets may
have intakes as high as 10.9 mg/day.
Manganese toxicity has not been observed in people eating Western-type or vegetarian diets,
hence the choice of this number as the cut-off.
However, it has been pointed out that determining manganese intake from different diets was
not the focus of this study, but it merely included a reference to a review that itself
referenced a single study from 1982 on 100 Canadian women, who were asked to report on
their own normal diet on 3 consecutive weekdays.
From this data, manganese intake was calculated and found to be as high as 10.8 mg.
So the upper limit set by the National Academy of Medicine is actually based off calculated
data and not actual measurement of intake, in this one observational study that did not
examine health status.
So it would appear that the tolerable upper intake level set by the Institute of Medicine
as they were known back then is not founded on very strong science, and it is not surprising
that other authorities have not set upper limits.
Additionally, manganese from food seems to be less absorbable and toxic than from contaminated
water, possibly by an order of magnitude or more, and manganese toxicity from food has
not been reported - remember, the basis for establishing an upper limit is from cases
of inhalation and water contamination.
We also appear to be able to adapt to a wide range of intakes by boosting or decreasing
absorption.
And even though manganese intake may be higher in healthier diets, these same healthy diets
may also provide protection against absorbing too much of this manganese - calcium, phosphorous
and phytate have all been reported to impair absorption of manganese, and are all found
in healthy whole plant foods.
All of this could be used to argue that perhaps the 11 mg tolerable upper intake level is
a bit too strict, but despite this I still recommend staying under this limit as much
as possible.
Manganese in water is thought to be more toxic than from food, but it is also possible that
water-borne manganese becomes even more toxic to those already consuming a lot of manganese
from food on a plant-based diet.
Another potential concern is that manganese may share absorption mechanisms with iron,
and it is possible that those who have developed iron deficiency anaemia as a result of a poorly-planned
plant based diet may increase their manganese absorption as an unintended consequence of
the up-regulation of iron absorption.
High manganese intake would also be problematic in the case of undiagnosed liver disease as
the liver's ability to eliminate the element becomes impaired.
Given all of these points, along with the knowledge that the consequences of manganese
toxicity are so severe and the fact that there is no good test for manganese status to titrate
level of intake, I recommend staying under the National Academy of Medicine's tolerable
upper intake level as much as possible.
I also recommend that you track your usual diet with Cronometer for a few days and have
a look at your manganese intake.
Make sure you aren't regularly exceeding the upper limit with your staple foods, and if
you are try to substitute some of them for foods lower in manganese.
In summary, those eating plant-based diets have a higher chance of exceeding the tolerable
upper intake level for manganese.
This level does not have a strong scientific basis, but given that the consequences of
excess are severe among several other factors, it is still best to take in less than this
amount.
It would be wise to determine your own intake, and modify your diet if it is too high.
Let me know in the comments if you've already tracked your manganese intake, and what kind
of level of intake you're getting!
Thanks for watching, and I hope this video has given you a better understanding of the
essential trace element manganese.
Be sure to share this video with anyone you know that might be worried about high manganese.
If there was something that wasn't clear from the video, feel free to let me know in the
comments and I'll get back to you.
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That's it for now though guys, talk to ye soon.
Sláinte!