How Glycemic Variability impacts HbA1c

Glycation: High GV has no significant effect on T2Ds. For T1Ds, its effect on Glycated Hemoglobin (HbA1c) is extremely minor the lower your mean glucose is. If your average glucose is 140mg/dL, then the difference between low and high variability on A1c is only 0.27%.

High GV has significant effects on glycation only at mean glucose levels far higher than most would find reasonable or properly managed:

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Please note: this thread was split from this post:


I’d like to add an anecdote to confirm the research on the relationship between glycation (A1c) & variability.

My CGM estimated A1c was 5.9-6.0% (eAG 120mg/dL) and my GV is a Standard Deviation of 54mg/dL or 22.5%. Neither loose nor tight control.

My tested A1c was 6.2%, which closely conforms to what the table predicts. A 0.2% higher A1c from the higher variability (although mine is 54mg vs 30, not 100 vs 30)

Would anyone else like to share their tested A1c, 3 month estimated A1c, and SD info? Does your discrepancy between estimated and actual also conform to the table above?

If A1c already accounts for the supposed negative effects of variability, then I wonder if the effects matter beyond what the A1c score already shows.

our son’s eAG for the last 90 days is 129 mg/DL and his SD was a poor 55 mg/DL, which corresponds to an estimated A1C of 6.1 or 6.2… His last measured A1C was 6.5. He consistently measures higher in terms of A1C than what his CGM data would predict; though I always assumed it’s because CGM data drastically overestimates the depth and duration of his lows.

So now I’m wondering if the glycemic variability is the source of those extra tenths of a point we always see on his A1C. But who knows.

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The research above said 100mg is high variability, 30 is low, so I wouldn’t beat yourself over 50 being too poor.

For non-diabetics it seems to be about 20mg
<6.5a1c T2D 30mg
>6.5a1c T2D 40mg+


But also, GV seems to have a minor overall effect compared to pre-meal and post-meal averages.


If the variability is on the high side and not the low, all the research so far shows it may be OK. All I find about chronic or severe hypoglycemia is not good.


Thanks for sharing. It does seem to conform to the idea that GV has a very modest glycation effect. I wonder what else may effect HbA1c then… a diet high in AGEs (Advanced Glycation End-Products)?

The most recent research I saw said that was a bit controversial as well, but worth looking into a low AGE diet, perhaps.

And… Nope, no effect on HbA1c from glycated foods:

(I’ve seen a study saying Hb-AGE and Hb-A1c are correlated in diabetics, but not in healthy people, so the cause-effect does not seem to start from food intake.)

Diasend doesn’t provide an estimated A1c. But my 90-day average is 7.6 mmol/L (136 mg/dl), 90-day standard deviation is 3.3 mmol/L (59 mg/dl), and my A1c taken a few days ago was 6.6%.


I was told the FDA told CGM makers (including Freestyle) they couldn’t say estimated a1c anymore, legally.
Regardless, I’m sure they just used the standard conversion factor:

28.7 X A1C – 46.7 = eAG

By the formula, you should have been 6.4%. Giving a possible effect of an extra 0.2% by your 59mg SD variability.

By the research, I’d expect the increase to be a little higher, actually! So maybe the theory doesn’t hold, but we’d need another 50 people to know!

But A1c in and of itself has some variation, doesn’t it? And don’t the most recent weeks have more of an impact on A1c than the first month?


I think the whole average bg equating to a specific expected a1c is a bit overrated as a concept…


@Jen you are right, there are multiple causes of a1c variation. I am just trying to see if glucose variability is a significant cause of that variation. It is assumed GV is bad because of extra glycation, without much proof. (And extra oxidation, also unproven.)
As for recent weeks having more impact [EDIT: this post split into the thread below]

14 posts were merged into an existing topic: HbA1c: do the latest BG samples count for more?