Blood Sugar 140: Where did the 140 mg/dL threshold come from?

This post (that is going to be a series to keep post lengths manageable) has been brewing for quite a while, but I was reminded of it because Jenny Ruhl came out with a diet book recently, and appeared recently as an "expert" on Jimmy Moore's Ask the Low Carb Experts podcast.  After listening to her previous podcast with Jimmy, I had some mixed reviews.  Jenny is certainly articulate, well-read (though I disagree, often strongly, with many of her interpretations) on the topic, and quite a bit more moderate/measured than most in her views on controlling diabetes with low carb.   But she also seems to view all diabetes through her own MODY eyes.  MODY (Mature Onset Diabetes of the Young) is a rare genetic form (there are actually several rare genetic forms classified as MODY) that is lumped quite often under the category of Type 1.5.  One of these days I need to address some other things on Jenny's website, as the site (and her book) is one of the commonly linked to internet resources for diabetes info in LC circles.    Her book, Blood Sugar 101, more specifically this Amazon review , as well as this page on her website, is where I took the title of this post from.  On the website she writes:
The studies you will read below, some of which are not cited in the AACE guidelines, make a cogent case that post-meal blood sugars of 140 mg/dl (7.8 mmol/L) and higher and fasting blood sugars over 100 mg/dl (5.6 mmol/L) cause permanent organ damage and cause diabetes to progress.
It is the first reference on this page that seems to be the original primary research source for the 140 mg/dL threshold ... a threshold that seems to have become somewhat ingrained as fact.

Increased Prevalence of Impaired Glucose Tolerance in Patients With Painful Sensory Neuropathy.   This study is cited under the bolded header and description that follows:

Nerve Damage Occurs when Blood Sugars Rise Over 140 mg/dl (7.8 mmol/L) After Meals
The University of Utah neurologists found that patients who were not known to be diabetic, but who registered 140/mg or higher on the 2-hour sample taken during a glucose tolerance test were much more likely to have a diabetic form of neuropathy than those who had lower blood sugars. Even more telling, the researchers found that the length of time a patient had experienced this nerve pain correlated with how high their blood sugar had risen over 140 mg/dl on the 2-hour glucose tolerance test reading.

It is important to note that this study also showed that only the glucose tolerance test results corresponded to the incidence of neuropathy in these patients, not their fasting blood sugar levelsmor their results on the HbA1c test.  This is significant because most American doctors do not offer their patients glucose tolerance tests, only the fasting glucose and HbA1c tests that fail to diagnose these obviously damaging post-meal blood sugars.
She is not alone in over-reaching with the results of this study.  In the Kindle version of Perfect Health Diet, the Jaminets write:
Nerve Damage Occurs When Blood Sugars Rise Over 140 mg/dl 

In a study of patients with peripheral neuropathy of unknown origin, neurologists found that many people who don’t have diabetes nevertheless have “diabetic neuropathy” – nerve damage from excess glucose. Moreover, when given a glucose tolerance test, how high blood sugars rose over 140 mg/dl was correlated with severity of the neuropathy. 30

Jaminet, Paul; Jaminet, Shou-Ching (2011-12-07). Perfect Health Diet: Four Steps to Renewed Health, Youthful Vitality, and Long Life (Kindle Locations 712-716). YinYang Press. Kindle Edition. 

There is a hat tip to Ruhl in the footnotes here. This is something Paul has repeated on the website and evoked during the "safe starches" debate::

In my main reply, I had written:  What is a dangerous level of blood glucose?
In diabetics, there seems to be no detectable health risk from glucose levels up to 140 mg/dl, but higher levels have risks. Neurons seem to be the most sensitive cells to high glucose levels, and the severity of neuropathy in diabetes is correlated with how high blood glucose rises above 140 mg/dl in response to a glucose tolerance test. [1] In people not diagnosed with diabetes, there is also some evidence for risks above 140 mg/dl. [2]
{emphasis mine}, and
In How to Minimize Hyperglycemic Toxicity:
What’s interesting to me here is that what we really care about is not the glycemic index, but the peak blood glucose level attained after a meal. It is blood glucose levels above 140 mg/dl only that are harmful, and the harm is proportional to how high blood glucose levels rise above 140 mg/dl. So it’s the spikes we want to avoid.
As mentioned previously, during my over three years now in LC internet circles, I've heard this 140 number innumerable times.  I've seen people worrying over doing irreparable damage to their cells and organs whenever  their blood glucose spikes over 140.  This is a case of a combination of what I would call scientific telephone and circular referencing.  Here we have one rather small study that has been blown way beyond all proportion as to its implications.

  • By "scientific telephone", I'm referring to the phenomenon that occurs when we play that telephone game as kids.  Remember that?  One person makes up a phrase then whispers it to the next person in a circle.  And around and around it goes until the last person whispers it back to the originator.  I don't recall a single instance from my childhood when the phrase made it around intact, and often it was horribly mangled.  
  • By circular referencing I am referring to the phenomenon that can occur sometimes where one source makes a claim and others repeat it enough that the claim becomes attributed to them, and the claim can even reach "I heard it somewhere" status because so many refer to it, formally or informally.  It's like those numerous famous quotes that nobody really knows who said it first.
I think many coming from the paleo side of things in this community associate that 140 mg/dL claim with Paul, if anyone at all ... while low carbers more with Jenny.  Mostly I just hear that number thrown around w/o attribution as if it is accepted common knowledge that blood glucose merely "spiking" over 140 is a bad, bad thing..

Indeed even the rather daunting conclusions of the study fall far short of implicating blood glucose spikes:
Our results suggest that IGT may cause or contribute to small-fiber neuropathy, which is similar in phenotype to the painful sensory neuropathy commonly encountered in diabetes. Two-hour OGTT is more sensitive than other measures of glucose handling in screening these patients.
So let's look at the study, shall we?  

The total study group numbered 107 subjects with "idiopathic neuropathy" -- idiopathic meaning of unknown origin.
The median age for the [...] patients was 64 ± 10.8 years (range 46–92), and 59 (55%) of these patients were women. Most patients (88) had exclusively sensory symptoms and signs; 76 reported neuropathic pain, and 12 reported no significant pain. The remaining 19 patients had symptoms and signs of distal weakness in addition to sensory symptoms.
Of the group only 72 subjects were evaluated with an OGTT (67% = 2/3rds of the study group, likely not relevant except that the effective study size is smaller).  As it turned out of the 72:   13 (18%) had Diabetes  ,  36 (50%) had Impaired GT  ,  23 (32%) had Normal GT

There were a number of other findings I'll address in follow-up posts.  One thing I'll say about the study itself at this time is that a study like this just begs for a control group of similar age.  To me this is a huge flaw in the study design.  This is an older group, and insulin resistance and IGT is prevalent in such a group to begin with.  For example, in this study (I found on a very quick search) of 65-74 year olds, 34-38% of the subjects had abnormal glucose tolerance.    Not a perfect comparison, but enough to get the idea.  Pick a random 65ish year old person off the street, roughly 1/3rd have IGT or worse.  Clearly amongst the painful neuropathy subjects, IGT & diabetes were more prevalent (roughly 2X vs. that study), but in the context of the prevalence of IGT in the aging in general, they are somewhat less "impressive".

In interpreting this study and its implications, I plan to address (in whatever order ends up working best):
  • The importance of context in extrapolating findings for measures like blood glucose levels.
  • What this study says (or does not say) about glucotoxicity (the actual blood glucose levels per se) vs. the potential underlying causes (e.g. insulin resistance) of the symptom (hyperglycemia)
  • What this study says (or does not say) about elevated glucose and the role of glycation in diabetes complications.
  • The utility of analyzing an "end point" study group for causative agents.  
In the end, I hope to present my case that this study does not provide much support, if any, for the contention that postprandial or transient glucose spikes over 140 mg/dL are damaging to neurons or other organs.

Follow-up post:  Blood Sugar 140: Context is Everything I - Diabetic vs. Non


Craig said…
To be clear - doesn't the 140 number refer to a test done two hours after a glucose tolerance test, not the peak (highest) level experienced? If you hit 140 after 2 hours, peak values could well have been much higher.

And to put this in perspective, what is "normal" response in a young healthy person? From reading Ruhl's site, I get the feeling that a young person with a health insulin response should be back to baseline (fasting levels) within 2 hours. So being 40 to 70 points above baseline after 2 hours could well indicate significant impairment of one's ability to properly metabolize glucose.
CarbSane said…
That's to be discussed in the "context" post, because yes, 140 after 2 hrs is indicative of metabolic problem, but not the same as glucose spiking over 140.
Karen said…
As a diabetic I am happy for a "number" to shoot for that has been at least shown to keep a person from problems. the number of 180 is evidently to high as there are many who keep their numbers there and still get neuoptropthy (sp). 140 is not an unattainable if a person keeps their carbs in check. I like Jenney a lot! She studies studies too, like you Ev. But from a diabetic point of view with the point to keeping appendages and eyes and kidneys and heart as intact as possible. Maybe the number is too low as far as that goes and could be higher without ramifications but still not normal. It may be to high but there its got to be better than the 180 ADA approves of.
CarbSane said…
Hi Karen! I can appreciate having a target to shoot for, but where is the evidence that 180 (peak) is too high? My next post in this series is dealing with context of that 140 number. I do believe that Jenny has taken that quite a ways out of context. The 140 is doable and not neurotically so, and I have no problem with anyone advocating that as a target -- it's responsible. I do have a problem with paranoia generating proclamations that a blood glucose level over 140 IS damaging. If it was, most T1's would have neuropathy by the time they're 20.
CarbSane said…
By the way, do you remember Griff from Jimmy's forum? He had a journal for a bit called Diabetes Begone or something like that. It's guys like him who come to mind when I hear these numbers, and others who are not diabetic that have the fear of God put into them when they read things like (paraphrase) "I know I'm doing permanent damage to my organs any time my BG goes over 140". It's almost impossible for that to be true.
Karen said…
I need to add to my post that sometimes meds are needed to keep bg down.

Hi Ev!!
I guess the evidence is experience (you all smart ones have a special name for that) People who do the ADA with lots of carbs and work their meds to cover them and have the "acceptable" HbA1c of 6+ are the ones with the damage. I cant read what studies mean to me most of the time they can say anything someone wants them to. LOL As Jenny says in her book an occasional foray out into high bg doesnt do the harm its daily letting it soar.

I do remember Griff and I do think Jimmy is not doing people a favor by saying to test your bg. Not everyone in the world needs to.

I think Ill stay at the 140 point with occasional ups. I know what my daddy went thru (yes I still call him daddy) and have no intention to go the same direction if at all possible. His bg was always 180 or above with insulin. He was miserable. Died of heart attack due to diabetes. Of course he didnt take care of his diet. Ate what he wanted when he wanted.
If you have an alternative I would sure like to hear it.
CarbSane said…
I can see from this response -- thanks for bringing this up! -- that in the next post I need to clarify diabetics v. non-diabetics. I think a 140 point is a far better target for diabetics than 180 (and when you say 180 are you saying all the time?). In the next post there's a graphic for normal blood glucoses, most don't go over 140 many do for short periods, and only a few go up to 160. So yeah, 140 as a target is targeting "normal" -- and if you err, you're not sending the BG train off the tracks.

It's more the non-diabetics that this value is a false threshold. Firstly if I eat X and my BG goes from 90 to 140, the impression is that I eat 2X it will go from 90 to 190, which isn't the case either. So people testing BG all the time and trying to avoid any spike over 140 lest nerve damage set in -- or even the spoken or unspoken threat that it will make one diabetic -- is more the point here. Also if my BG were to spike above 140 (never happened when I tested, though I'm quite sure it's gotten higher at some points in my life) it would come down within a half hour or at worst an hour which is not the case for the diabetic (especially w/o meds).

I'm glad Jenny says that about occasional forays. From listening to her podcast (haven't listened to the new ones yet) and reading some of her articles, she's much more moderate and open to using meds when prudent than many take her. And yet she can be quite extreme, as with the header on the discussion of this study -- that 140 causes nerve damage -- when the study said nothing of the sort. I was also rather disappointed in her take on the crash diet study calling it "dangerous" and saying moderate low carb would have the same effect when that's simply not true.

I think BG testing is useful to know where you're at. I have been meaning to check my own as it's been quite a long while and I still have that meter around here somewhere. But I think the LC community on the whole obsesses over BG WAAAAAAAAAAAY too much.

Hugs backatcha!
Karen said…
On her website she is definately posting to diabetics. I wasnt talking about non-diabetic but read your blog thru diabetic eyes :)) Im with you not everyone needs to test. Diabetics best friend is test test test. Jimmys concern about his bg "spiking" to 90-100 after a meal is laughable! My husband 6'1'', 175 after a heavy meal has allowed me to test his just for kicks and its usually around 95 at 2hr pp but drops much further at 2hr15min.
OnePointFive said…
This comment has been removed by the author.
OnePointFive said…
During the last 3 months my HbA1c was 5.7% which is an estimated average glucose level of 117mg/dl. It's a good average for a 'T1' (target normally 7%) but I certainly have some very low glucose levels, below 60mg/dl and few (very few) levels that are above 200mg/dl My levels normally range between 65mg/dl and 155mg/dl .What is important to me is that both extreme lows and highs are very short lived.
If blood glucose levels stay high then that would be reflected in the HbA1c and from everything I have seen it's that that seems to be the risk factor for complications.

There is no consensus about the role of spikes in 'causing' complications. It is a continuing debate but so far there is very little evidence to support the idea that intra day variability(ie spikes)are related to either micro or macro vascular complications in either T1 or T2.

Arguments for and against the Role of Glucose Variability in the
Development of Diabetes Complications

Glycemic Variability: Can We Bridge the Divide Between Controversies
Monnier & Colette

Glucose variability; does it matter?
Siegelaar SE, Holleman F, Hoekstra JB, DeVries JH

It seems ridiculous for non diabetics to start worrying about the odd spike and certainly about levels that are very much normal.
One study showed young non diabetics spending an average of 11.6 min a day above 140mg/dl

A second study using 80 non diabetics, with an average age of 41 found that nearly all of them exceeded 7.8 mmol/l (140 mg/dl) at some point during the day and spent a median of 26 min per day above this level. They also found that one in ten reached diabetic levels (11.1 mmol/l, 200 mg/dl).
Sheena Williams said…
Are medications really works to control blood sugar level.
Ardy Hagen said…
Can we agree the diabetes has negative health implications?
That observation seems uncontroversial.

And there is no bright line for diagnosing diabetes IIS. There it's an arbitrary value
It is a semi-arbitrary value the same way Jenneys reference to 140 watcher is an arbitrary value not as if something magical happens at 140 as opposed to 139 or 138 or 144

If Jenny had used value of 800 it would not be having this dispute. We would not be having a dispute because it would obviously be an incredibly unhealthy value for any normal person to have a blood sugar Value of 800

Well what if she'd selected 400 is our arbitrary number once again argue that we wouldn't have this discussion because once again 400 Is Way too high number and everyone would intuitively realize that if you had a Blood sugar value of 400 is unhealthy

Well what if Jenny had selected an arbitrary value of 200 and said that's unhealthy value. Once again I don't think we would be having an argument because it's intuitively obvious value of 200 is not normal.
Ardy Hagen said…
The number 140 for blood glucose is an arbitrary number the same way that diagnosing diabetes itself is based upon some arbitrary number

Nothing magical happens at 140
nothing magical happens at 130
and nothing magical happens at 150
but at some point higher blood glucose levels are not normal and they're harmful to our health

There is no magic blood-pressure that suddenly becomes unhealthy but at some point higher blood pressure is not a good thing

There is no magic weight at which a person becomes obese and Therefore unhealthy as a result. but still it is true that if you weigh a thousand pounds probably it's not healthy for you

Did jenny misstate or overstate something, perhaps
Ardy Hagen said…
But the bottom line is still pretty much the same isn't

If you are having excessive blood sugar spikes
whatever excessive means to you
Then at some point that likely indicates some sort of medical problems that will cause you health complications.

If you are experiencing excessive spikes in your blood sugar
And most likely your insulin system is not working entirely correctly
Most likely you were developing some degree of insulin resistance
And most likely you're on the path towards having diabetes II

And what ever it is about diabetes that causes people health problems
Those health problems are likely in your future if you do nothing
carbsane said…
Can we agree the diabetes has negative health implications?

Sure we can. But there's a huge difference between frank diabetes and transient hyperglycemia.

And there is no bright line for diagnosing diabetes IIS. There it's an arbitrary value

It is a semi-arbitrary value the same way Jenneys reference to 140 watcher is an arbitrary value not as if something magical happens at 140 as opposed to 139 or 138 or 144

I agree with the first point to a degree. But it almost does seem to be a pretty bright line when pancreatic function declines to the point of not being able to maintain glycemic control.

Jenny's 140 is based on the study here. But she is taking it out of context. She didn't select it arbitrarily is my point. And it is the cut-off for the standard OGTT delineating normal from impaired glucose tolerance at the 2 hour mark.

My argument is not about 200, it is about 140.
carbsane said…
I just went back and edited in a link to the followup:
Blood Sugar 140: Context is Everything I - Diabetic vs. Non

What defines excessive? This is where misuse of this cut-off has many thinking that any time their BG spikes over 140 that is excessive and it is putting them at risk for neuropathy (and diabetes?). Check out the graphic of glucose levels for a number of normal people. Varies widely. Seems to me the more important thing is "does it come back down".

If your 2 hour OGTT is around 140, then you likely have a problem. I'd check the 1 hour as this is probably more predictive of already impaired insulin secretion.

You might be interested in this post:

Also, this post has links to all four Blood Sugar 140 posts:
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