Blood Sugar Levels: How to Keep Them Stable and Why It Matters for Health
Articles
A stable blood sugar level is key to both physical health and mental well-being. Sharp swings in blood glucose can lead not only to fatigue, irritability and sugar cravings, but in the long term also to more serious problems: from insulin resistance through hormonal imbalance and cardiovascular problems to type 2 diabetes, and in the long run even Alzheimer's disease.
What will you learn from this article?
- Why is a stable blood sugar level important?
- What should your blood sugar level be?
- How blood sugar swings can show
- What raises blood sugar?
- Low blood sugar (hypoglycaemia)
- Blood sugar and metabolic health
- How does blood sugar affect female hormones?
- How stress affects blood sugar
- Blood sugar swings and ageing
- Glycated haemoglobin and why it is worth measuring
- Does blood sugar differ with age?
- Practical tips for stabilising blood sugar and reducing health risks
- Key takeaways
Why is a stable blood sugar level important?
Glucose is the preferred source of energy for most cells in our body, especially the brain and muscles. For the body to use it efficiently, blood sugar has to be kept within a fairly narrow range, between 3.9 and 5.6 mmol/l when fasting. With balanced blood glucose, we feel focused, have enough energy and our organs work optimally. A stable blood sugar level also protects the blood vessels and nervous system and affects hormonal balance. Blood glucose, the concentration of "sugar" in the blood, is therefore one of the basic indicators of metabolic health.
On the other hand, blood sugar swings trigger physical stress and burden the organs, especially the pancreas and liver, and can set off a chain of further health complications. Exposing cells to high blood sugar for too long also leads to glycation of tissues and to their damage. In this process, sugar molecules bind to proteins and fats, creating harmful substances known as advanced glycation end products (AGEs).
Stable blood glucose levels are achieved through a complex system of hormonal regulation. The main role in keeping blood sugar balanced is played by two hormones released by the pancreas: insulin and glucagon. If the glucose regulation system fails and levels become too high (hyperglycaemia) or too low (hypoglycaemia), dysregulation sets in, leading to a cycle of metabolic and hormonal disorders that can damage organs and lead to serious diseases.
When blood glucose rises, for example after a meal but also because of stress, the pancreas starts to release the hormone insulin. It works like a key that unlocks the cells, mainly in the muscles and fat tissue but also in the liver, and allows them to absorb glucose from the bloodstream for energy or storage.
At the same time, insulin suppresses the production of new glucose in the liver. When blood sugar starts to fall, the pancreas releases glucagon. This hormone signals the liver to break down stored glycogen and release glucose back into the blood (a process known as glycogenolysis). This feedback system stops the body from slipping into hypoglycaemia.
A breakdown of the whole system and insulin resistance of the cells, marked by the inability to store excess glucose, leads in the long term to a number of diseases and type 2 diabetes.
At first, however, there may be no symptoms at all. If the body has insulin resistance but the pancreas can still produce insulin, it simply produces more of the hormone. Over time, however, the pancreatic cells become exhausted and can no longer produce insulin. This naturally leads to raised blood glucose levels.
What should your blood sugar level be?
Blood sugar does not stay the same throughout the day. It naturally changes depending on food intake, physical activity and hormones. In a healthy person, however, these changes stay within a range that provides enough energy for the cells and protects the body from the negative effects of blood sugar that is too high or too low.
Which values are considered normal, and which are not?
| Measurement | Range |
|---|---|
| Fasting | 3.9–5.6 mmol/l |
| 2 hours after a meal | up to 7.8 mmol/l |
| Prediabetes (fasting) | 5.6–6.9 mmol/l |
| Diabetes (fasting) | ≥7.0 mmol/l |
| HbA1c (glycated haemoglobin) | <39 mmol/mol |
What should your fasting blood sugar be?
Fasting blood sugar is a basic indicator of glucose metabolism. It is measured after at least 8 hours without food and is one of the most common laboratory tests. A normal fasting value is 3.9–5.6 mmol/l.
Higher values may point to prediabetes or diabetes, but how they are interpreted always depends on other lab results and your overall health.
What should your blood sugar be after a meal?
After a meal, blood glucose naturally rises. In a healthy person, however, insulin brings it back to normal within a few hours. A value of up to 7.8 mmol/l two hours after a meal is considered normal.
If blood sugar repeatedly rises sharply or stays raised for a long time, this may be the first sign of reduced insulin sensitivity.
How blood sugar swings can show
Blood sugar swings are marked by a sharp rise in blood glucose after a meal, followed by a rapid fall. When tracked with a glucose meter, this can be pictured as a so-called "Gothic arch" curve. The swings can show up both in the short and the long term. This mainly happens after eating foods with simple, quickly absorbed carbohydrates and no fibre, such as sugary soft drinks, sweets and ice cream, but also sweet fruit such as bananas and pineapple, or after pasta and other carbohydrate side dishes such as rice and potatoes. This is also why we recommend starting the day with a protein-rich meal. Want to know more? Read our article What to eat for breakfast: and why you should focus on protein.
This can then lead to:
- Short-term symptoms: fatigue, irritability, poor concentration, headaches, sugar cravings.
- Long-term consequences: repeated overloading of the pancreas, insulin resistance and the inability of cells to respond to insulin, inflammatory processes in the body due to circulating blood sugar, storage of glucose in fat reserves and damage to blood vessels.
The more sugar the body takes in, the deeper the swings become, which raises the risk of chronic diseases. A rapid rise in blood sugar after a sweet meal (especially when the source is simple sugars and industrially produced foods such as sweets and soft drinks) triggers an excessive release of insulin. Insulin then lowers glucose levels, but often too far, which leads to hypoglycaemia. At this point, the body starts releasing the stress hormone cortisol, which supports gluconeogenesis, the production of glucose from non-sugar sources, mainly in the liver. Often, however, people also feel a loss of energy and fatigue, which leads to cravings for more "sweets" with fast sugars. The vicious circle of blood sugar swings deepens further.
These swings are an enormous stress load for the body, leading to increased production of free radicals, oxidative stress and micro-inflammation. All of these factors gradually damage the blood vessel walls, speed up atherosclerosis and raise the risk of cardiovascular disease. They also contribute to a higher risk of developing Alzheimer's disease.
What raises blood sugar?
Many people think that only sweets raise blood sugar. In reality, a whole range of factors affects it.
The most important include:
- simple carbohydrates and a high intake of refined grains
- lack of fibre
- a sedentary lifestyle and lack of exercise
- chronic stress
- lack of sleep
- acute infection and inflammation
- some medicines (for example corticosteroids)
- excess weight and obesity
- alcohol and smoking
The order in which you eat the different parts of a meal also plays an important role.
Low blood sugar (hypoglycaemia)
Low blood sugar, medically called hypoglycaemia, occurs when the glucose concentration in the blood falls below 3.9 mmol/l. Glucose is the main source of energy for the brain and muscles, so a lack of it can show quite quickly. Hypoglycaemia occurs most often in people treated with insulin or some diabetes medicines, but it can also occur in healthy people, for example after a long period without food, very intense physical activity, or a sharp rise and subsequent fall in blood sugar after eating a large amount of simple carbohydrates.
The most common symptoms of hypoglycaemia include:
- sudden hunger
- shaking, sweating and a pounding heart
- fatigue, weakness and dizziness
- poorer concentration
- irritability or mood changes
With a more pronounced drop in blood sugar, vision problems, confusion, poor coordination or, in extreme cases, loss of consciousness may also occur. This condition needs immediate treatment.
In healthy people, the body effectively prevents a drop in blood sugar with the hormone glucagon, which stimulates the release of stored glucose from the liver. At the same time, more stress hormones are produced, especially adrenaline and cortisol, which help raise glucose levels again.
Blood sugar and metabolic health
Unstable blood sugar is directly linked to the development of metabolic and cardiovascular diseases, for several reasons.
- Insulin resistance and type 2 diabetes: these develop because cells stop responding to insulin and cannot store the circulating glucose. As a result, blood glucose stays chronically higher, which causes oxidative stress and leads to inflammatory processes in the body.
- Cardiovascular disease: this is a consequence of raised blood glucose and insulin resistance, which promote inflammation in the blood vessels and the formation of atherosclerotic plaques through the action of cholesterol, which in turn contributes to high blood pressure.
- Excess weight and obesity: these are caused by blood sugar swings, which increase appetite and promote fat storage, especially around the abdomen. Excess glucose and fructose that is not used for energy is stored in fat reserves and liver tissue, gradually leading to non-alcoholic fatty liver disease. Excess body fat then further promotes a chronic inflammatory state in the body.
- Chronic hyperglycaemia can ultimately cause irreversible and extensive damage to nerves, blood vessels, tissues and organs, affecting the microvascular and macrovascular health of the whole body. Microvascular complications mainly affect small vessels and include retinopathy (damage to the retina), nephropathy (kidney damage) and neuropathy (nerve damage). Macrovascular complications mainly affect large vessels and can lead to serious conditions such as coronary heart disease or stroke.
How does blood sugar affect female hormones?
Blood sugar swings affect not only energy and mood, but also women's hormonal balance. Long-term unstable blood sugar can reduce the sensitivity of cells to insulin, promote inflammation and indirectly affect the production and action of sex hormones.
Oestrogen, progesterone, androgens and blood sugar
Unstable blood sugar is linked to worse premenstrual syndrome (PMS) symptoms, more painful periods and greater fatigue. These changes are driven partly by increased inflammation in the body and by hormonal imbalance.
In some women, blood sugar swings may also contribute to an irregular menstrual cycle, poorer ovulation quality or a worse course of polycystic ovary syndrome (PCOS).
In women with PCOS, stable blood sugar plays an especially important role. Insulin resistance, which is very common in this condition, promotes increased androgen production in the ovaries. This can worsen symptoms such as irregular periods, acne, excessive hair growth or fertility problems. Keeping blood sugar balanced is therefore one of the basic steps in supporting women's hormonal balance and reproductive health.
How stress affects blood sugar
Psychological and physical stress lead to an increased release of stress hormones, especially cortisol and adrenaline. These hormones help the body cope with demanding situations by promoting the release of glucose from the liver into the bloodstream, providing a quick supply of energy for the muscles and brain.
If stress lasts for a long time, however, cortisol levels stay raised for longer. This can lead to chronically higher blood sugar, reduced insulin sensitivity of the cells and the gradual development of insulin resistance.
Unstable blood sugar also creates a vicious circle. When blood glucose falls sharply after a meal, the body treats the situation as stressful and starts producing more cortisol. Cortisol then promotes the release of glucose into the blood to provide enough energy. Repeated activation of this mechanism can contribute to fatigue, disrupted sleep, increased inner tension, poorer recovery and reduced resistance to stress.
Blood sugar swings and ageing
Unstable blood sugar also speeds up ageing processes: both the more visible ones (skin ageing and loss of elasticity) and the less obvious ones (atherosclerosis, protein glycation). The main causes are increased oxidative stress, the formation of glycated proteins and chronic inflammation.
- Oxidative stress: caused by an excess of unused glucose in the body, which leads to higher production of free radicals. These then damage DNA and other cell structures.
- Glycated proteins (AGEs): with long-term raised glucose levels, sugar "sticks" to proteins (glycation), which reduces tissue elasticity and damages blood vessels, skin and nerves. All of these factors contribute to faster ageing and a higher oxidative load.
- Chronic inflammation: large sugar swings also keep an inflammatory environment in the body, which is one of the main drivers of faster biological ageing and further damage to health.
- The gut microbiome: high blood sugar also has a negative effect on the gut microbiome. It leads to an imbalance in the microbiome and can cause increased intestinal permeability, known as "leaky gut".
- In the long term, the formation of AGEs also affects cognitive decline and the ability to remember information. AGEs therefore play a significant role not only in diabetes and cardiovascular disease, but also in neurodegenerative disorders such as Alzheimer's disease. A high AGE load contributes to faster brain ageing, memory loss and a worse course of neurodegenerative diseases.
Glycated haemoglobin and why it is worth measuring
An excessive intake of simple carbohydrates and free sugars in the diet, which are not bound to fibre and are not used up, for example, during exercise, means that a large amount of unstored glucose circulates in the body. Sugar molecules then bind to proteins such as collagen and elastin.
Protein glycation is also a major factor contributing to microvascular and macrovascular problems. Tissue damage is especially visible in the kidneys, the retina and the peripheral nerves. A large amount of these sugar-damaged proteins also impairs the uptake of glucose by the cells and contributes to insulin resistance.
The cycle of oxidative stress and glycation also damages the beta cells of the pancreas, which produce insulin. This further speeds up the onset of type 2 diabetes. The scientifically proven link between glycated proteins and type 2 diabetes is clearly visible in measured levels of glycated haemoglobin.
A process similar to the one we know from the kitchen, when baking bread or roasting meat, can take place in our body: the so-called Maillard reaction creates the brown "crust" and typical aroma. For our own health, however, it is a negative sign of excess glucose. In the body, this reaction leads to the formation of advanced glycation end products (AGEs), which build up in tissues, damage proteins so they stop working properly, speed up cell ageing and contribute to complications of diabetes, cardiovascular and neurodegenerative diseases.
Measuring AGEs directly in the blood is not common, so measuring glycated haemoglobin (HbA1c) serves as a simple indicator of the body's exposure to excess glucose. It shows how much the body is currently exposed to sugar, while the formation of AGEs is the long-term, harmful consequence of this state.
That is why we recommend regular HbA1c blood tests. It is one of the simplest and at the same time most useful preventive tests, as it shows your average blood glucose levels over the past 2–3 months.
An HbA1c value of 39 mmol/mol or higher signals the first signs of prediabetes. At this stage, it is still possible to reverse the process with lifestyle changes (diet, exercise, good sleep, etc.) and so prevent type 2 diabetes from developing.
Does blood sugar differ with age?
Reference blood sugar values are the same for most healthy adults regardless of age. In older age, however, doctors often set individual target values for patients with diabetes, because blood sugar that is too low carries a higher risk of falls, loss of consciousness and other complications for older people.
Blood sugar in older adults
For healthy older adults, the same reference values apply as for younger adults: 3.9–5.6 mmol/l. For people treated for diabetes, target values may be slightly higher, especially if they have other chronic conditions.
Blood sugar in children
In healthy children, blood sugar regulation is very similar to that of adults. Fasting reference values in most age groups are roughly 3.9–5.6 mmol/l, and their correct interpretation always depends on the child's age, the time since their last meal and their overall health.
Because of their higher energy needs and faster metabolism, children naturally have larger blood sugar swings during the day. Short-term fluctuations after physical activity, a longer gap between meals or during an acute illness do not always mean a health problem.
However, if a child repeatedly shows symptoms such as marked thirst, frequent urination, unexplained weight loss, excessive fatigue or repeated episodes of hypoglycaemia, it is advisable to see a doctor. These can be among the first signs of glucose metabolism disorders, including type 1 diabetes, which most often develops in childhood.
Practical tips for stabilising blood sugar and reducing health risks
The composition of a meal, the ratio of macronutrients (protein, fat, carbohydrates) and a simple change in the order in which you eat can have a big impact on blood sugar stability after eating.
Protein has minimal impact on raising blood sugar after a meal. The advantage is that when you eat a complete meal based on good protein sources, together with healthy fats, blood glucose does not rise as sharply even if you eat carbohydrates at the same time.
Fat in the diet also slows glucose absorption by delaying stomach emptying. It is best to focus on healthy fats such as avocado, olive oil or oily sea fish, regularly and in reasonable amounts, ideally combined with good-quality protein and complex carbohydrates.
The main macronutrient that breaks down into glucose, and so directly affects blood sugar levels, is carbohydrates. The amount of carbohydrates you eat and their type (simple vs. complex) has a major influence on the rise in blood glucose after a meal.
Fibre also plays a key role in blood sugar regulation. Enough fibre in the diet slows the digestion and absorption of carbohydrates, improves insulin sensitivity and protects against sharp blood sugar swings, supporting a lower long-term risk of type 2 diabetes and cardiovascular disease. We recommend an optimal fibre intake of 25–35 grams a day for adults.
How to reduce the risks of blood sugar swings
Diet:
- Start your meal with vegetables or protein, eat the carbohydrates last and combine them with healthy fats. This leads to a slower rise in blood glucose after the meal, a smaller energy dip and more stable blood sugar.
- Choose foods with a low to medium glycaemic index and a higher fibre content.
- Avoid simple sugars and industrially processed foods that contain them.
- A simple trick that also helps stabilise blood sugar after a meal is drinking a spoonful of apple cider vinegar in a little water shortly before eating, which supports digestion.
- We also recommend limiting foods rich in AGEs: grilled, fried and industrially processed foods.
Lifestyle:
- Regular exercise improves the sensitivity of cells to insulin.
- Good sleep and stress management help keep hormones and blood glucose stable.
Supplementation:
- Chromium contributes to the maintenance of normal blood glucose levels and zinc to normal carbohydrate metabolism. Magnesium and berberine are also often mentioned in this context.
- Omega-3 fatty acids EPA and DHA contribute to the normal function of the heart.
- We also recommend supporting the body's natural antioxidant capacity: vitamins C and E contribute to the protection of cells from oxidative stress, and polyphenols and astaxanthin are other popular antioxidants.
Key takeaways
Stable blood sugar is the foundation of overall health: it is not only important for preventing diabetes, but also affects our energy, hormonal balance, mental health and the ageing process.
Blood sugar swings can damage the body in the long term: unstable blood sugar burdens the blood vessels, nerves and metabolism and can contribute to lifestyle diseases.
Sharp blood sugar spikes overload the body: marked swings can burden the pancreas and promote the body's stress response, inflammation and faster ageing.
Unstable blood sugar is linked to many health problems: in the long term, it can contribute to insulin resistance, type 2 diabetes, obesity, and cardiovascular and hormonal problems.
The type of carbohydrate matters: simple carbohydrates cause a sharp rise in blood sugar, while complex carbohydrates and fibre help provide a steadier supply of energy.
Everyday lifestyle supports healthy blood sugar: a balanced diet based on good-quality protein, complex carbohydrates and healthy fats, regular exercise, good sleep and stress management all help.
It is worth monitoring glycated haemoglobin: HbA1c shows the body's long-term sugar load and can help detect a problem before more pronounced symptoms appear.
Sources:
[1] Hanssen NMJ, Kraakman MJ, Flynn MC, et al. Postprandial Glucose Spikes, an Important Contributor to Cardiovascular Disease in Diabetes? Frontiers in Cardiovascular Medicine. 2020;7:570553. doi:10.3389/fcvm.2020.570553. https://www.researchgate.net/figure/Hypothetical-glucose-curves-of-an-untreated-patient-with-diabetes-A-and-after_fig1_345010880
[2] Verywell Health. The 4 Stages of Type 2 Diabetes. Reviewed by Rita Kalyani. Updated 2024. https://www.verywellhealth.com/stages-of-type-2-diabetes-6503545
[3] Ceriello A, Esposito K, Piconi L, et al. Oscillating glucose is more deleterious to endothelial function and oxidative stress than mean glucose in normal and type 2 diabetic patients. Diabetes Care. 2008;31(2):e15. https://pmc.ncbi.nlm.nih.gov/articles/PMC4384119/
