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This is another article about the important canine nutrition topic of blood glucose (sometimes called “blood sugar”) in dogs. For a more general introduction to this subject and an explanation of why it is so important for pet owners to understand it, you’ll want to check out this earlier article too.
Here we’re going to focus on a specific blood glucose question that we often hear from dog owners: what constitutes a “normal” or “healthy” blood sugar level for a dog?
There are definitely direct, evidence-based, numerical answers to that question and we’ll get to them in due course. But let’s start with some context.
What Is Blood Glucose?
Glucose is a very simple kind of carbohydrate molecule. In fact, it’s the building block of all carbohydrates. What we call “complex carbs” are those that are composed of long, intricate chains of glucose molecules. While “simple” carbs are composed of just a few. But, fundamentally, all carbs are made up of glucose molecules arranged in one way or another.
Naturally, when we say “blood glucose,” we’re referring to the glucose molecules that are circulating in your dog’s body in its bloodstream.
Where Does Blood Glucose Come From?
Glucose is quite literally the stuff of life. It is the single most important source of metabolic fuel in all organisms, not just dogs. Without glucose, plants wouldn’t grow and snakes wouldn’t slither, and dogs wouldn’t play around and bark and poop in the living room.
A helpful analogy is to think of your dog’s body as a city, with each vital organ being a different building that’s important for the city to function. In this analogy, your dog’s circulatory system is like the city’s network of roads and highways and glucose is one of the many different kinds of cars on the roads. These cars drive around on the roads until they are needed at one building or another, whereupon they cruise over to the relevant building and go inside to do whatever work needs to be done.
The glucose in your dog’s blood comes from two different kinds of sources. The first are called “exogenous” sources, meaning those originating outside of the body. By far the most common exogenous source of excess glucose, is – you guessed it – food! More specifically, dietary carbohydrates. Recall that carbs are made up of chains of glucose molecules. So when your dog eats a carbohydrate-rich meal, she is ingesting a whole bunch of lengthy glucose chains. Those chains get broken down into individual glucose molecules during digestion, which then get absorbed into the bloodstream, causing blood sugar levels to rise.
But blood sugar can also come from “endogenous” sources, meaning those originating inside of the body. Through highly-evolved metabolic wizardry, your dog’s body can actually make glucose out of other kinds of molecules. In this regard, the most important kinds of molecules are proteins, which under certain conditions get converted into glucose through an intricate bodily process called gluconeogenesis. In the absence of dietary carbs (if your dog consumes an all-meat diet), a healthy dog will produce all of the glucose it needs from gluconeogenesis and other internal bodily processes – which is why carbs are not considered essential nutrients for dogs.
Function and Dysfunction in Blood Glucose
So if glucose is a key source of metabolic energy, is it optimal for your dog to have an abundance of it in the blood all the time?
No. In fact, if blood sugar levels get too high it is not just bad for your dog’s health but acutely toxic. If blood sugar levels get too high, your dog will suffer seizures, slip into a coma, and eventually die. In high quantities, glucose is quite literally a deadly poison.
Okay, so if too much glucose is bad for your dog, is it optimal for your dog to have none of it in the blood at all?
Also no. In fact, having too little glucose in the blood is also deadly. When blood sugar levels get perilously low dogs don’t have enough metabolic fuel in the body to do the things they need to do to stay alive (keep their hearts pumping, etc.).
This means that your dog’s body has to be really, really good at keeping blood sugar levels balanced within a pretty narrow range. And, fortunately, it is! The primary “tool” that is used to keep blood sugar at healthy levels is a hormone called insulin.
Insulin is made by the pancreas and its primary function is to drive glucose out of the blood and into other tissues (like fat cells and muscles), where the glucose can be stored safely in a non-toxic form. Essentially, when blood sugar levels get too high, the pancreas notices and begins secreting more and decreased glucose production and more insulin, until the blood sugar levels come back down again. Phew, crisis averted.
At least if your dog is healthy. If, on the other hand, the animal is diabetic, then its pancreas does not produce insulin effectively enough. As a result, if your dog has diabetes, there’s often not enough insulin being produced to bring blood sugar back down to tolerable levels. So when blood sugar levels get too high (like after a carbohydrate-rich meal) they stay too high. And that can cause big-time health problems for diabetic dogs, as explained above.
This is why one of the main treatments for canine diabetes is giving your dog shots of exogenous insulin. These shots supplement whatever amount of insulin the pancreas can make endogenously, helping to bring your dog's blood sugar levels back down to earth.
Do Blood Glucose Levels Stay Stable For Long Periods of Time in Dogs?
No, not really. In fact, it’s important to understand that blood sugar levels are almost never stable, in dogs or in humans. They tend to fluctuate significantly throughout the day in response to all kinds of different stimuli, including physical activity, sleeping, and ingesting a meal.
If, at any point in time, your dog has “high blood sugar” (the technical term is hyperglycemia) that just means that there’s lots of glucose in the bloodstream at that particular time, while “low blood sugar” (hypoglycemia in dogs) means there’s relatively little glucose in the blood at that point.
Taken together, all this means that there isn’t really a single, specific blood sugar level that is considered healthiest for dogs. Because even in dogs with totally normal, healthy metabolic systems, the glucose level is constantly changing. Instead, when we talk about healthy blood sugar levels in dogs we are talking about a range of values—and if your dog’s blood glucose falls anywhere within the range, that is generally considered ideal.
What is a “Healthy” Blood Glucose Range for Dogs?
Because health isn’t a very concrete concept, the short answer to this question is “it depends who you ask.”
According to the American Animal Hospital Association, the “normal” range of blood sugar levels for a healthy dog is 80-200 mg/dl. As such, by the AAHA’s definition, a blood sugar level below 80 mg/dl is considered too low and a level consistently above 200 mg/dl is considered too high.
But not everyone agrees with the AAHA.
For instance, the authors of this study (two academic vets from Australia) assert that “clinically normal” dogs typically maintain blood sugar levels of between 60 and 111 mg/dl. But even they acknowledge that observable clinical signs of hypoglycemia in dogs (low blood sugar) don’t typically arise unless the animal’s blood sugar falls below 50 or even 40 mg/dl.
And the authors of this study (researchers at Auburn University) found that the vast majority of the 53 healthy, nondiabetic dogs they evaluated maintained blood sugar levels between 76 mg/dl and 116 mg/dl.
Moreover, while carbohydrates are the backbone of the modern pet food industry, healthy dogs that don’t consume much dietary carbohydrate at all rarely have blood sugar levels above 100 mg/dl. (See this study for more on this subject).
Obviously, there’s a good deal of overlap in these various ranges. But there’s a pretty meaningful difference too. Specifically, while many experts think that dogs cross over into unhealthy metabolic territory once their blood sugar levels exceed about 110 mg/dl, the AAHA thinks there’s nothing wrong until the animal’s blood sugar is almost twice that high.
So who’s right?
The Final Answer
In light of all the available evidence, we think the best answer is as follows: for optimal health, a dog’s blood glucose levels should stay between about 60 and 110 mg/dl.
You’ll notice that this is a somewhat narrower and lower range than the one endorsed by the AAHA. There are two primary reasons for this.
The first is that while acute hyperglycemia (and its scary consequences, such as seizures and coma) may not be a serious risk until blood sugar levels get well above 200 mg/dl, sudden and deadly health consequences aren’t the only kinds of risks tied to blood sugar.
Long-term, chronic health conditions (notably obesity, diabetes, and cancer) all have direct ties to glucose metabolism too–and generally the risks all rise as blood glucose concentration levels rise. So while you may not have to worry about your dog slipping into a diabetic coma if its blood glucose concentration peaks at 200 mg/dl, that doesn’t mean that it’s optimal for chronic disease avoidance and long-term health optimization for its blood sugar to be that high.
The second reason we disagree with the AAHA is “normal” doesn’t necessarily mean “healthy” or “optimal.” In fact, in America today, the norm is for dogs to be profoundly unhealthy. The same long-term chronic diseases linked to glucose metabolism just happen to be afflicting pet dogs at epidemic levels.What a coincidence! Blood glucose levels as high as 200 mg/dl may be common among modern dogs, but modern dogs also tend to eat an abundance of dietary carbohydrates and die of chronic diseases like cancer. So “normal” likely isn’t the best target here.
As such, while a blood sugar reading between 110 mg/dl and 200 mg/dl may be perfectly fine from the AAHA’s perspective, we think the evidence suggests that dogs are considerably healthier when they maintain low blood sugar levels of between 60 and 110 mg/dl. And that’s your final answer.
How to Learn More About Low Blood Sugar in Dogs
If you want to optimize your dog’s health and longevity, it pays to go deeper into the subject of blood glucose. It’s a complex subject and there’s a lot to know! Fortunately, we’re here to help. Here are links to some other articles we have prepared that touch on blood glucose test, sugar and metabolism in one way or another: