Medically reviewed by Dr. Mike Natter.
Almost everyone who lives with diabetes is already familiar with the A1C test. Your A1C is an estimate of your average blood sugar levels over the previous several months; many people with diabetes are originally diagnosed with the results of an A1C test. It is still the most important benchmark for glucose management success, and is the primary way that your medical team will evaluate the success of your treatment.
The American Diabetes Association categorizes blood sugars by A1C like so:
Normal – below 5.6 percent
Prediabetes – 5.7 to 6.4 percent
Diabetes – 6.5 percent or above
For the most part, everyone in the diabetes world agrees that a lower A1C is better than a higher one. Higher A1C’s are correlated with a quicker onset and increased severity of complications, and it is well-known that lowering A1C correlates with decreased risks. But is there such a thing as too low?
This article is written for primarily people with diabetes, of any type, that use insulin or sulfonylureas, which are insulin mimetics. Both drugs can cause hypoglycemia. Readers that do not use either drug are at a significantly lower risk of hypoglycemia – much of the following discussion will not apply.
The Official Recommendations
The ADA begins with a blanket recommendation for all adults with diabetes: aim for an A1C level of <7.0%.
This goal, however, may be adjusted based on several other factors. Making this adjustment can be more art than science, and is something best decided with the help of your primary care doctor or endocrinologist. There is no official guidance on precisely how to weigh additional considerations, but the following image from the ADA gives an idea of how these different factors can influence glycemic targets:
Source: ADA, Standards of Care 2021
The phrase “more stringent” here refers to a more rigid or demanding glucose control strategy, generally characterized by aggressive use of insulin and other glucose-lowering medications in order to keep a patient’s blood sugar closer to the non-diabetic range. By contrast, a “less stringent” approach means a less intensive glucose control strategy, which necessarily entails higher blood sugars.
In advising a certain A1C target, your doctor will attempt to balance your risk of hypoglycemia against your risk of hyperglycemia, among other factors.
Younger patients with fewer health issues are probably better equipped to set a lower A1C target and choose a more stringent regimen. They also may have a better reason to do so: they know that they have decades of life with diabetes in front of them, an awfully long time to develop complications.
Older patients, or those that already have more serious health issues, may be advised to target less stringent glucose control. Elderly patients, for example, may be less capable of perceiving the symptoms of hypoglycemia. This severe and immediate danger of low blood sugars may outweigh the long-term danger associated with chronic hyperglycemia. And, sad as it is to say, older patients may have less reason to worry about some of the slow-developing complications of diabetes, because they may not live long enough to suffer from them.
There may be other special factors at play, too. For example, women who are pregnant or planning to become pregnant are advised to attempt much tighter blood glucose control, because we know that tighter A1C goals are correlated with fewer fetal complications.
The Argument for a 6% A1C
It’s fair to say that most doctors will be pleased to see any of their (non-pregnant) patients with diabetes achieve an A1C at or just below 7.0 percent. Doing so without an unusual amount of glycemic variability (extreme blood sugar highs and lows) confers significant reductions in the risk of diabetic complications. Only a minority of patients with diabetes reach that benchmark, typically after considerable effort.
But a smaller minority of people with diabetes reason that an A1C just below 7.0 percent is just not good enough. They believe that further decreasing their A1C level, down towards the non-diabetic range, will provide the most protection against diabetes-related complications, or perhaps even prevent them completely.
The science mostly backs this theory up. The ADA confirms that “further lowering of A1C from 7% to 6% is associated with further reduction in the risk of microvascular complications,” although it cautions that there are some diminishing returns: “the absolute risk reductions become much smaller.”
If you can achieve a 6% A1C without an undue risk of hypoglycemia, that appears to be best for your health, especially if you have a longer life expectancy.
As there are numerous health advantages to maintaining “normal” blood glucose levels, it seems like keeping blood glucose in the normal range as much as possible is a reasonable goal, if it can safely be achieved.
And how about an even lower A1C? Many healthy adults without diabetes have A1C’s around 5.0%, sometimes even lower. Is that a reasonable target for a patient with diabetes? Is it safe?
Strict Glucose Control and The Danger of Hypoglycemia
Many doctors and diabetes experts assume that a very low A1C is dangerous because it necessarily involves an elevated risk of hypoglycemia. It makes sense: why wouldn’t targeting lower blood sugar increase the likelihood of very low blood sugar?
Much evidence has been found to support this contention, including what may be the most famous and important type 1 diabetes trial ever conducted. The Diabetes Control and Complications Trial (DCCT) was the experiment that definitively linked chronic high blood sugar with the accelerated development of diabetic complications; it solidified the recommendation that people with type 1 diabetes ought to employ “intensive” insulin management to promote long-term health.
But the DCCT also showed that intensive management entailed “a threefold increased risk of hypoglycemia.” And we’re not talking about minor low blood sugar events that the patients easily treated themselves with a little candy or juice. This was “severe hypoglycemia,” defined as hypos that require the assistance of others, including those that end in seizure, coma, and emergency medical treatment. Nevertheless, the experts concluded that the downside of increased risk of hypoglycemia was far outweighed by the long-term health gains associated with intensive management.
Even so, the fear that more aggressive insulin management might result in even more severe hypoglycemic events has helped inspire diabetes authorities to recommend glycemic control in that 6.5-7.0 percent A1C range as a sort of happy medium.
Strict Glucose Control Without Enhanced Hypoglycemia Risks?
A growing chorus of voices in the diabetes community – both doctors and patients alike – believes that it is possible to achieve a much lower and even normal A1C, and to do it without meaningfully increasing the risk of severe hypoglycemia.
In 2018, a team of researchers and low-carbohydrate advocates took a close look at one such group, members the Facebook group TypeOneGrit. Members of TypeOneGrit are dedicated to the treatment strategies of Dr. Richard Bernstein, an influential diabetes doctor that advises a very-low carbohydrate diet as the lynchpin of a complex treatment strategy.
The findings were published in the medical journal Pediatrics. Group members that participated in the study had an average A1C of 5.67 percent, almost exactly at the threshold of pre-diabetes, and far better than any glycemic target ever recommended by diabetes authorities. The ADA’s most recent official guidance on glycemic targets do not address lower A1C goals for patients with type 1.
But was it safe? Critically, patients observed in the study also reported “low rates of hypoglycemia and other adverse events,” suggesting that their extremely stringent approach did not increase the danger of overtreatment with insulin. The article called the results “without precedent,” a sentiment that was echoed in major media coverage. But this was merely a small observational study – not a rigorous double-blinded and randomized trial – and authors also caution that the “generalizability of the findings is unknown.”
The Importance of Glucose Variability
A1C is only one part of the blood glucose picture. Another important element is glucose variability – how wildly your blood sugar swings up and down. A patient with a low variability will only experience mild blood sugar swings, while one with a high variability will experience much greater swings both above and below their ideal range. Generally speaking, the less glycemic variability, the better.
Patients with very low glucose variability have an enhanced ability to stay steady at a lower blood glucose level – say, 80-100 mg/dL – without risking severe hypoglycemia. For a patient with high glucose variability, the same blood sugar level could get dangerous very quickly.
Glucose variability is best measured with a continuous glucose monitor. One way to ensure that a lower A1C was not achieved with severe hypo risk is to review your blood sugar readings with your healthcare professional. With CGM data (or very fastidious use of a blood sugar meter), it should be plain to see how often any patient experiences dangerous hypos.
The smartphone apps for the Dexcom and Freestyle Libre systems track glucose variability with statistics such as “standard of deviation” and “coefficient of variation.” You can find more detailed commentary on these numbers in this article from our friends at DiaTribe.
How does one lower their glycemic variability? The folks examined in the Pediatrics article described above were committed to a very-low-carbohydrate diet, which both reduces postprandial glucose spikes and also allows patients to use less mealtime insulin, lowering the risk of postprandial glucose lows. Dr. Bernstein has influentialy described this as “the law of small numbers.” Several past and present members of the Diabetes Daily staff have followed the same philosophy with success, as have many of our readers. But the evidence in favor of this approach remains mostly anecdotal.
The Bottom Line
You should set your own A1C goal in partnership with a healthcare professional. There are many individual factors that your doctor will take into consideration, including your age, your health, and your risk of severe hypoglycemia.
Blood glucose levels at or approaching the “normal” range (defined as an A1C below 5.6 percent), although not commonly recommended by diabetes authorities, are associated with a lower risk of long-term complications. For some patients, it may be reasonable to employ stringent glycemic control in the hopes of bringing blood glucose levels down towards the normal range.
However, attempted stringent control can also bring an enhanced risk of hypoglycemia, especially with management strategies that do not sufficiently reduce glycemic variability. Patients should proceed very carefully, and with full cooperation of their medical team before initiating any changes to their diabetes regimen.