What is a normal blood sugar level is a question I am asked so often. My patients have heard so many conflicting numbers over the course of their diabetes lives.
Historically, the target was set at 4-7mmol/L but in more recent teams this has widened to a looser 4-10mmol/L. However, there are some big exceptions to this rule that need discussing.
Before we go any further, let me just explain something. Blood sugar levels and blood glucose levels are interchangeable expressions. Therefore, from this point on if we switch between the 2 terms it means the same thing. The reason for the change is because blood sugar levels is by far the more searched term in Google. However, blood glucose levels is technically the correct term.
It frustrates me to find generic glucose targets given to patients regardless of their diabetes type, age, length of diagnosis etc. Surely it makes sense to modify the target based on the patient sat in front of you.
In the specialist diabetes clinic this is exactly what happens. Hence why if you were comparing notes with a peer about what a normal blood sugar level is, you may find they differ.
However, there are generic blood sugar targets that we can aim for with a few caveats. Therefore, I wanted to write this article to explain what a normal blood sugar level is in the context of those caveats so you can be crystal clear on what you should be aiming for.
Types of diabetes
First of all, we need to appreciate there are lots of different types of diabetes and each will be treated differently. Think about it, type 2 diabetes has at least 6 different oral medications you can take and the option of insulin, which is also the treatment for type 1 diabetes (and most type 3c diabetes).
Each medication behaves differently in the body and it is often the effect of these medications which helps guide our targets. Typically, medications that can result in low blood sugars, like insulin and sulphonylureas (both linked if you want to know what these are) will mean your targets are set a bit higher. This helps to build some margin into your target range if your dose is a little off.
Your historical glucose control may also factor into this. If you have ran high glucose levels for some time, your team may recommend reducing your levels gradually. Alternatively, if you have low levels, they may recommend aiming a bit higher to help build that margin into your targets to prevent further hypos.
Furthermore, an 85 year old may have looser targets compared to a 25 year old. Without sounding too morbid, the likelihood is the 25 year old has to live longer with diabetes than the 85 year old. Therefore, their targets may be a bit stricter.
Blood glucose targets
If I had a penny each time a patient told me their targets are 4-7mmol/L. Often, this dates back decades gone by where they were told this in like 1955 and have followed this target ever since.
So what’s wrong with this?
Well, first of all, if you actually monitor someones glucose levels without diabetes, you’ll find their glucose fluctuates between 3.5-10mmol/L. So such targets are asking for better glucose control than someone without diabetes!
Now I know these targets are designed to be pre meal so I’m being a bit perdantic. The idea being the glucose levels should settle about 4-5 hours after eating. However, remember diabetes is the inability to control your blood glucose levels. So if you have diabetes and are aiming for 4-7mmol/L all the time, you’re swimming against the tide. Especially, when your counterpart without diabetes, will see higher glucose levels throughout the day greater than 7mmol/L.
So first things first, lets broaden this target slightly. A glucose target of 4-10mmol/L works just as well as 4-7mmol/L. It places no extra risk of developing long term complications but is much more realistic.
A Normal blood sugar level
We can categorise blood sugar levels into 3 categories. Low, normal and high. However, we’ve addressed some caveats already but I’m going to throw a couple more at you, which also need to be considered.
Low blood sugar level
We have a saying in diabetes called 4 is the floor. This is because we don’t want your glucose levels dropping below 4mmol/L. If this happens you can start to feel symptoms of hypoglycaemia. This is when you become shaky, sweaty, tingly and in severe cases, cognitively impaired and even unconscious.
However, this is only true if you are taking medications that cause low blood sugar levels. Basically, insulin and sulphonylureas (generally end in zide or mide – link here all about them).
Otherwise, hypos are not a problem and you will unlikely even be asked to check your blood glucose levels on a daily basis. We only ask patients to do that for low blood sugar risk. High glucose levels will be identified on your HbA1c.
In fact, we’ve already established someone without diabetes may experience glucose levels below 4mmol/L. This is normal and likely happens to most people if we tested their glucose levels day to day. Therefore, 4mmol/L is the floor only if you take the above medications, which may cause low blood sugars.
You may experience symptoms of a low blood sugar at 4mmol/L but a true hypo isn’t until glucose levels are even lower than this. Therefore, the idea is we build some margin into your target glucose levels. In fact, often we’ll aim for 5mmol/L and above.
Without taking medications that can result in hypoglycaemia, don’t panic if you see a glucose level slightly below 4mmol/L. The likelihood is it is a normal result, just like anyone else in the population.
If you are repeatedly symptomatic of hypoglycaemia with a low blood sugar level, despite taking no insulin or sulphonylurea, speak with your medical team. However, this is very unlikely.
Normal blood sugar level
We’ve mentioned above that someone without diabetes can and will experience glucose levels between 3.5-11mmol/L.
The old 4-7mmol/L target refers to pre meal tests. The idea being your glucose has had a chance to settle back to this level by the next meal. NHS guidance advises a 2 hour post meal glucose of 8.5-9mmol/L. This is nearer to what someone without diabetes would experience. However, their glucose levels would likely come back between 4-7mmol/L much quicker than this.
In the context of diabetes, if your blood sugar level remains elevated between 7-9mmol/L for a while, don’t worry too much. In the realms of diabetes, this is still great glucose control. Just be aware, that your glucose levels may gradually increase throughout the day if they slowly nudge themselves up with each meal.
If you’re taking insulin, achieving such a target of 4-7mmol/L will likely cause hypos. Think about it. If you’re glucose is 4.5mmol/L it only takes a 1mmol/L drop to be in a hypo. Whereas, if you aim a bit higher, maybe 5-9mmol/L, a 1mmol/L builds in some margin without increasing your long term complications risk.
If you’re not taking insulin or sulphonylureas your target will likely be more to do with the HbA1c test as you won’t be routinely monitoring your glucose levels day to day. More on this shortly.
Diabetes isn’t actually diagnosed until glucose levels rise above 11mmol/L on a finger prick test (7mmol/L if it is fasting). Therefore, by definition, a high glucose level is anything over these ranges.
That said, if you have type 1 diabetes and take insulin, your diabetes team will likely be quite happy with a waking glucose of 7mmol/L. This builds in that margin for low blood glucose levels and is a pretty good start to the day in the context.
Furthermore, if your highest glucose level is 12mmol/L, actually it’s likely you’re quite well controlled. Sure, your glucose level is a little bit high. Higher than ‘normal’ and diagnostic of diabetes. However, on average, you’ll likely have good glucose control.
The further away from normal you get the more serious the condition may become over the long term. If your glucose level is 25mmol/L quite regularly, you can see this is a lot over target. Now your complication risk starts to increase. Therefore, high glucose levels require context.
Another important factor is what is your average glucose control. A blood sugar level of 25mmol/L is high but if your average control is good, then you’re still doing fine. Luckily we can assess this using the HbA1c test.
In short the HbA1c looks at your average glucose control over the previous 3 months. We can do this because glucose sticks to your red blood cells and red blood cells last 3 months before being recycled.
Therefore, we can test how much glucose has stuck to the red blood cells in the previous 3 months to give us an average.
The HbA1c test is directly related to your finger prick test but it is providing a different measurement. A normal level on a finger prick of 4-10mmol/mol, will translate to a good HbA1c result. Conversely, persistently high finger prick results will directly link to a high HbA1c result.
The HbA1c test is measured in both mmol/mol and a percentage. Each percentage rise is equivalent to 11mmol/mol. A Hba1c of 48mmol/mol (target range) is equivalent to 6.5%. Therefore, to calculate the difference, each 1 percent increase to your HbA1c score, just add 11mmol/mol and vice versa. In the UK we now use the mol/mol method and the percentage system is slowly being phased out.
Low HbA1c levels
The HbA1c test isn’t without its flaws. First of all any haemaglobinopathies (problems with the red blood cells) such as sickle cell disease or even anaemia will effect this result and can render it unrealiable.
Therefore, really low values, often below 20mmol/mol likely indicate something else is going on.
Normal HbA1c levels
Pre diabetes is diagnosed with a HbA1c of 42mmol/mol. Therefore, a HbA1c of 42mmol/mol or above is considered abnormal. Diabetes is diagnosed with HbA1c of 48mmol/mol.
Someone without diabetes usually has a HbA1c ranging from the low twenties to 41mmol/mol. Of course, the closer you get to that pre diabetes range, the more likely you will go on to develop pre and actual diabetes later in life.
The target range for glucose control in diabetes is between 48-53mmol/mol. This is as good as it gets in the realms of a diabetes diagnosis. A Hba1c of up to 59mmol/mol is still considered good control. However, as the Hba1c starts to rise above this, the chances of developing complications also starts to increase. This risk of complications is directly proportional to how high your glucose go.
A one off high HbA1c isn’t the end of the world. So we’re really looking at your lifetime average.
The temptation for everyone with diabetes is to try to normalise their glucose levels back below 42mmol/mol. This is a good goal but it does depend on your treatment and type of diabetes.
Type of diabetes effecting targets
We know people with type 2 diabetes do have a chance of pushing their diabetes into remission and thus achieve normal glucose levels once again. This is dependent on their length of diagnosis and treatment but it is possible. I’ve written an article on it here.
However, people with type 1 diabetes or who are taking insulin need to be careful. Achieving normal glucose levels below 48mmol/mol or even 42mmol/mol without hypoing is nearly impossible, though some achieve it.
Often, these hypos are undetected. This is because until recently we couldn’t use continued glucose monitoring technology and also when you run your glucose levels super tight, you lose hypo awareness.
Hypos should not be ignored. They can be dangerous and also contribute to cognitive decline over time. People with cardiovascular conditions should also be cautious as there is a link between hypos and cardiac events.
Furthermore, when we look at the evidence, there isn’t really much difference for long term complications by achieving a HbA1c below 48mmol/mol. In this context, when we refer to long term complications, we are referring to high glucose levels.
Therefore, patients doing this are 1) increasing their hypo risk and 2) are likely having to pay laser focus to their glucose levels each day for actual limited additional benefit medically. This can impact quality of life scores and so a balance of good glucose control to having some flexibility in your glucose levels is often advised.
High HbA1c levels
We know what a normal HbA1c result is now. In practice, I doubt many of your health care team will be too worried if your HbA1c is around the 59mmol/mol (7.5%) mark.
However, as it starts to rise above this their concern may start to increase. The further away you get from target range, the more likely you’ll eventually start to experience longer term complications of the disease.
This is of course related to the duration your glucose levels remain high. A one off blip over a lifetime will unlikely be a problem. A persistent high level will likely cause a problem eventually. So think of it as an average.
Neglecting your glucose levels at some point of your life can still effect the complication rate later in life, even if you have improved your control later. This is because all the HBA1c results feed into your average. This doesn’t mean making improvements will not be beneficial at any stage in your life. However, it can mean that some complications related to diabetes could emerge related to previous high glucose levels. The speed at which complications occur will be directly related to how high your glucose levels go and how long they stay there.
This is why your medical team will appear very eager to help you lower any high glucose results.
One draw back of the HbA1c is it is only an average. Therefore, 2 people can have the same HbA1c with very different day to day glucose levels. One person may have a HbA1c of 48mmol/mol and run glucose levels of 5-9mmol/L. Another person may have a HbA1c of 48mmol/mol but could run glucose levels between 2-25mmol/L. This is mostly likely to happen with insulin use and therefore will likely be picked up with daily finger prick tests.
Post meal glucose levels
One last thing to discuss is the difference between post meal glucose rises between people with and without diabetes.
Patients with very good glucose control will still likely see longer post meal rises in their glucose levels compared to someone without diabetes.
This is for 2 reasons. First, people with diabetes struggle to achieve normal glucose levels. Their body isn’t working in such a way that the body can easily deal with food as it previously had. Second, medications for treating diabetes are good but they aren’t quite as good as what the body is capable of without diabetes.
Below is a diagram from our video above demonstrating some examples of a post meal glucose response.
Excuse the bad art. However, as you can see we have 3 different glucose examples after eating a meal. Though there are additional ways glucose levels may respond. This is just to highlight some key points.
In green, the person with diabetes sees a rise in their glucose levels but it comes back very quickly.
Someone with well controlled diabetes (in blue) may see a similar rise but they are often unable to bring them back down as quickly. It’s not unusual for someone with a good HbA1c to range between 5-11mmol/L. However, they may spend more time towards the upper end of the range. As opposed to someone without diabetes who will likely spend most of their time at the lower end of the range.
Then we have the person in red. They see a rise above normal after eating. This is then followed by a drop back into normal range or the glucose remains elevated going into the next meal.
Over the course of the day, the person in red is much more prone to either persistently high glucose levels or erratic levels that fluctuate up and down. Such fluctuations are usually associated with the use of insulin because the food and insulin doses are not matching up.
As you can see, there are many different factors that go into what defines a normal blood sugar level. This depends on your diagnosis, type of treatment, length of duration, age and the list goes on.
The key element is having open discussions with your health care team about what is a good target blood sugar level for you. You can then begin working towards this and hopefully have a great quality of life, whilst living with diabetes.
Need more help?
If you need more support we offer a range of 1:1 consultancy services and online programmes focused on helping you improve your glucose control and health for the long term. These include our type 2 diabetes recovery programme, type 1 glucose stability programme and winning weight loss programme. Go to the pages using the links above or in the headers or get in touch if you have questions.