Research Connecting Organ Damage with Blood Sugar Level
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.

NOTE: All blood sugar levels discussed on these pages refer to plasma calibrated meter readings which are the readings used by all meters sold in the United States. In other parts of the world where blood calibrated are still in use, including the UK, users should divide the numbers given here by 1.12 to get the blood calibrated equivalents.

Nerve Damage Occurs when Blood Sugars Rise Over 140 mg/dl (7.8 mmol/L) After Meals

A study conducted in the neurology clinic at the University of Utah examined patients who came to the clinic complaining of peripheral neuropathy of unknown origin. Peripheral neuropathy is the medical term for a kind of nerve damage which causes pain, tingling, "pins and needles" or burning sensations in the hands and feet.

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 levels or 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.

Increased prevalence of impaired glucose tolerance in patients with painful sensory neuropathy. Singleton, JR Smith AG, Bromberg, MB Diabetes Care 24 (8) 1448-1453 2001.

A second study performed by neurologists at Johns Hopkins confirmed these findings. Fifty-six percent of their patients who had neuropathy of unknown origin were found to have abnormal results on their oral glucose tolerance tests. When nerve conduction studies were run, doctors sorted their patients into those whose glucose tolerance test results were normal, those with impaired glucose tolerance whose 2-hour glucose tolerance test readings fell between 140 mg/dl and 200 mg/dl, and those who were diabetic, with two hour glucose tolerance test results were above 200 mg/dl (11.1 mmol/L). They found that patients who had impaired glucose tolerance had experienced damage to their small nerve fibers while those with diabetic-level test results had more involvement of the large nerve fibers.


The spectrum of neuropathy in diabetes and impaired glucose tolerance. C.J. Sumner, MD, S. Sheth, MBBS MPH, J.W. Griffin, MD, D.R. Cornblath, MD and M. Polydefkis, MD; Neurology 2003;60:108-111.

Yet another study, conducted at the Mayo Clinic in Scottsdale, AZ and published in August 2006 confirmed these results. In addition they documented that the fasting plasma glucose test identified only half as many people with abnormal blood sugars as the glucose tolerance test.

Value of the Oral Glucose Tolerance Test in the Evaluation of Chronic Idiopathic Axonal Polyneuropathy. Charlene Hoffman-Snyder; Benn E. Smith; Mark A. Ross; Jose Hernandez; E. Peter Bosch. Arch Neurol. 2006;63:1075-1079.

Analysis of data from the MONICA study found this incidence of neuropathy in a population of roughly 400 people only half of whom had been diagnosed with diabetes.

The prevalence of neuropathy was:

28.0% in the diabetic subjects

13.0% in those with Impaired Glucose Tolerance (2 hr GTT = or > 140 mg/dl)

11.3% in those with IFG (Fasting glucose > 100 mg/dl)

7.4% in those with Normal Glucose Tolerance (2 hr OGTT < 140 mg/dl this suggests to me that a blood sugar of 125-139 two hours after eating is probably high enough to cause neuropathy and should not be defined as normal.)

In the entire population studied (n = 393), age, waist circumference, and diabetes were independent factors significantly associated with polyneuropathy, whereas in the diabetic group polyneuropathy was associated with age, waist circumference, and peripheral arterial disease (PAD)

Prevalence of Polyneuropathy in Pre-Diabetes and Diabetes Is Associated With Abdominal Obesity and Macroangiopathy Dan Ziegler et al. Diabetes Care 31:464-469, 2008


Keeping Blood Sugars Below 140 mg/dl at All Times Improves Survival of Seriously Ill Patients

Dr. Krinsley decreased the mortality of a group of critically ill patients by 29.3% simply by keeping their blood sugar below 140 mg/dl at all times using insulin. This intervention also cut down the incidence of kidney failure and shortened the patients' stay in the ICU. In numbers this means that 45 people out of a group of 800 left the hospital alive who would have died had they adhered to the ADA's standards for blood sugar control.
Krinsley, James, Effect of an Intensive Glucose Management Protocol on the Mortality of Critically Ill Adult Patients. Mayo Clinic Proc. Jan 2004, p. 992-1000.


Beta Cell Destruction Begins at 2-hr OGTT Test Readings Over 100 mg/dl (5.6 mmol/L)

When a team of Italian researchers led by A Gastardelli started examining beta cell response to glucose in people with normal blood sugars, they discovered that a small amount of beta cell dysfunction began to be detectable in people whose blood sugar rose only slightly over 100 mg/dl on a 2-hour glucose tolerance test. The beta cells are the cells in the pancreas that produce the insulin your body uses to control your blood sugar.
Analyzing their data further, they found that with every small increase in the 2-hour glucose tolerance test result, there was a corresponding increase in how much beta cell failure was detectable. The higher a person's blood sugar rose within "normal" range, the more beta cells were failing.

It is important to remember, though, that the 100 mg/dl here is a value taken 2 hours after drinking the 70 or 75 g of glucose administered in the glucose tolerance test. What really does the damage isn't that 100 mg/dl, it's the much higher blood sugars that were present during the previous 2 hours while the glucose was in the bloodstream. It is also important to remember that glucose is metabolized much more quickly than the carbs in food which need time to be digested, so a person who ends up with a 100 mg/dl reading 2 hours after a glucose tolerance test may see readings of 130 to 150 at two hours after eating a high carb meal containing the same amount of carbohydrate.

Beta-cell dysfunction and glucose intolerance: results from the San Antonio metabolism (SAM) study. Gastaldelli A; Ferrannini E; Miyazaki Y; Matsuda M; De Fronzo RA;Diabetologia 2004 Jan;47(1):31-9


Beta Cells Die Off in People Whose Fasting Blood Sugar is Over 110 mg/dl (6.1 mmol/L)

An intriguing study shows the severe organ damage experienced by people whose blood sugar falls into a range most doctors consider to be near-normal. A team of researchers autopsied the pancreases of deceased patients who were known to have had fasting blood sugars that tested between 110 mg/dl and 125 mg/dl within two years of their deaths. The researchers found that these patients, whose blood sugar was not high enough for them to be diagnosed as diabetic, had already lost, on average, 40% of their insulin-producing beta cells.

Since the American Diabetes Association believes that a fasting blood sugar level of 100 mg/dl to 125 mg/dl corresponds to a 2-hour glucose tolerance levels of 140 mg/dl to 199 mg/dl, this suggests that patients whose post-meal blood sugars rise only to the non-diabetic "impaired" level may be well on the way to losing as much as 40% of their beta cell mass. It also suggests that people with abnormal glucose tolerance who wish to avoid further beta cell loss should try to keep their blood sugars under 140 mg/dl at all times.

However, it is important to understand that in any study that measures only fasting blood sugar and finds a correlation with complications, it isn't the fasting blood sugars that are doing the damage when they are under 140 mg/dl.

The reason slightly elevated fasting blood sugars correlate with beta cell destruction is that people with slightly elevated fasting blood sugars who eat high carbohydrate meals are experiencing high, and often long lasting, blood sugar spikes after each meal they eat. A 210 lb person whose fasting blood sugar is 110 needs to eat only 12 grams of carbohydrate to raise their blood sugar to 150, and most of them are likely to be eating 50 to 60 grams of carbohydrate per meal, ensuring that their blood sugars are well over 150 for several hours after each meal.

It is those high post meal readings that go along with elevated fasting levels that cause the glucose toxicity that damages organs and causes complications.

Beta-cell deficit and increased beta-cell apoptosis in humans with type 2 diabetes. Butler AE, Janson J, Bonner-Weir S, Ritzel R, Rizza RA, Butler PC.Diabetes. 2003;52:102-110.