What Level of Blood Sugar Is Dangerous?

Maintaining stable blood sugar levels is crucial for overall health. Both excessively high and low blood sugar levels can lead to severe health issues if not managed promptly. For those with diabetes or at risk of blood sugar imbalances, knowing what constitutes a dangerous level is essential. This guide explores the thresholds for dangerous blood sugar levels, their symptoms, causes, and what to do if levels are too high or too low. 

Understanding Blood Sugar Levels 

Blood sugar, or glucose, is the body’s primary energy source. It fuels everything from brain activity to muscle movements. Levels are measured in millimoles per litre (mmol/L) in the UK and Ireland. Normal blood sugar levels vary slightly depending on the individual, their activity, and the time of measurement [3]. 

• Normal fasting levels: 4.0–5.4 mmol/L 

• After eating: Less than 7.8 mmol/L 

What happens when levels deviate? 

When blood sugar levels fall below or rise above the normal range, the body struggles to function efficiently. Blood vessels, organs, and nerves are particularly vulnerable. Persistent abnormalities can lead to chronic conditions or acute emergencies. 

What is Hyperglycaemia? 

Hyperglycaemia occurs when blood sugar levels rise too high. For most people, this is defined as levels exceeding 10 mmol/L after eating or 7 mmol/L when fasting. It is especially concerning for people with diabetes, as it can lead to serious complications if not addressed promptly. 

Why does hyperglycaemia happen? 

Hyperglycaemia typically results from insufficient insulin production or the body’s inability to use insulin properly [1] [5]. Contributing factors include: 

• Eating large amounts of sugary or carbohydrate-rich foods. 

• Forgetting to take prescribed insulin or medication. 

• Experiencing stress, which triggers a release of hormones that increase blood sugar. 

• Underlying infections or illnesses. 

Signs to watch for: 

• Increased thirst and dry mouth. 

• Frequent urination, especially during the night. 

• Fatigue or general weakness. 

• Blurred vision. 

If left untreated, severe hyperglycaemia can lead to diabetic ketoacidosis (DKA), a potentially life-threatening condition where the body breaks down fat for energy, producing harmful acids called ketones. Symptoms of DKA include fruity-smelling breath, nausea, and confusion. 

What Is Hypoglycaemia? 

Hypoglycaemia, or low blood sugar, occurs when levels fall below 4.0 mmol/L. It can develop rapidly and is especially common in people taking insulin or certain medications for diabetes. However, it can also occur in non-diabetic individuals under specific conditions [2]. 

Common causes of hypoglycaemia: 

• Skipping meals or prolonged fasting. 

• Exercising without consuming adequate food beforehand. 

• Taking too much insulin or diabetes medication. 

• Drinking excessive alcohol without eating enough food. 

Symptoms of hypoglycaemia: 

• Shakiness and trembling. 

• Sweating, even in cool conditions. 

• Difficulty concentrating or feeling confused. 

• Sudden hunger and irritability. 

Severe hypoglycaemia can result in fainting, seizures, or even a coma if not treated promptly. Recognising these warning signs and acting quickly is essential. 

Symptoms of dangerous blood sugar levels 

Recognising the symptoms of abnormal blood sugar levels is the first step toward preventing complications. 

Symptoms of high blood sugar include: 

• Persistent fatigue despite resting. 

• Nausea or vomiting. 

• Rapid heartbeat or palpitations. 

• Slow-healing wounds or recurrent infections. 

Symptoms of low blood sugar include: 

• Sudden mood changes, such as irritability or anxiety. 

• Pale, clammy skin. 

• Tingling in the lips, tongue, or fingertips. 

• Loss of coordination or balance. 

Ignoring these signs can lead to serious complications like organ damage or loss of consciousness. 

Causes of abnormal blood sugar levels 

Blood sugar levels can fluctuate for many reasons, even in healthy individuals. Below are some of the most common causes: 

1. Dietary choices 
   Eating foods high in sugar or carbohydrates can cause rapid spikes. Similarly, skipping meals can lead to dangerously low blood sugar levels. 
2. Medication errors 
   Taking incorrect doses of insulin or oral medications for diabetes is a frequent cause of blood sugar imbalances. 
3. Stress and illness 
   Physical stress, like an infection or injury, triggers the release of stress hormones, which can raise blood sugar levels. 
4. Lifestyle habits 
   Overexertion during exercise without proper nutrition can lower blood sugar, while poor sleep can disrupt the body’s natural glucose regulation [4]. 
5. PCOS 
   Hormonal changes can affect blood sugar levels, making them go up or down. People with PCOS may have a condition called insulin resistance, where their bodies don’t respond to insulin as well as they should. Long-term use of steroid medications can also lead to weight gain and a condition called Cushing's syndrome. 

How to stabilise blood sugar levels safely 

Proper management of blood sugar levels requires consistency and attention. Here are steps you can take: 

For hyperglycaemia: 

• Drink water to help flush excess sugar from your bloodstream. 

• Adjust your insulin dosage if prescribed. 

• Reduce carbohydrate intake until levels normalise [1] 

For hypoglycaemia: 

• Consume fast-acting glucose, such as a sugary drink, glucose tablets, or a small piece of fruit. 

• Follow this with a more substantial snack, like whole-grain bread or nuts, to sustain blood sugar levels [3]. 

Routine monitoring with a glucometer can help you stay aware of your levels and prompt you to take action when required. 

When to seek medical help 

Certain situations require immediate medical intervention [1]. Seek help if: 

• Blood sugar levels remain consistently above 15 mmol/L or below 3 mmol/L. 
• You experience confusion, fainting, or severe nausea. 
• Symptoms of diabetic ketoacidosis, like fruity breath and severe stomach pain, occur.

Delaying treatment in these cases can result in life-threatening complications, such as organ failure or a diabetic coma. 

Understanding what constitutes a dangerous blood sugar level is vital, especially for those managing diabetes. Both hyperglycaemia and hypoglycaemia can lead to emergencies if untreated. Knowing the warning signs and taking quick action, such as adjusting diet, medication, or seeking medical advice, can prevent complications. 

How HealthHero can help 

If you’re concerned about your blood sugar levels or overall health, easily schedule an online GP consultation. Our experienced doctors can assess your condition and provide professional advice. Whether you need guidance on blood sugar management, prescriptions, or general health concerns, we're here to help.