Low blood sugar without diabetes is uncommon, and when it happens it is usually linked to a long gap without food, alcohol, hard exercise, a dip a few hours after a sugary meal, or a medicine. Below 4.0 mmol/L is the level Diabetes Australia's NDSS treats as a hypo. Repeated or severe lows need a GP to find the cause.
If you have a reading from a finger-prick meter or a CGM, check where it sits against Australian ranges.
For people with diabetes, a glucose level below 4.0 mmol/L is a hypo and should be treated straight away. Healthdirect uses the same cut-off. People without diabetes generally sit between 4.0 and 7.8 mmol/L across the day, according to Diabetes Australia.
Without diabetes, doctors look for more than a number. The Endocrine Society's guideline asks for Whipple's triad: symptoms of a low, a low glucose measured in a blood sample at the time, and symptoms that go away once glucose is raised. A single low reading on a home device, with no symptoms, is not enough to diagnose hypoglycaemia.
In people without diabetes, the body is good at holding glucose up. The liver releases stored glucose between meals and overnight, and hormones such as glucagon, adrenaline and cortisol step in when levels fall. A true low happens when something overrides that system. The common causes are:
Less common causes need a doctor to find them. The Endocrine Society lists critical illness (severe liver, kidney or heart failure, sepsis and starvation), hormone deficiencies such as low cortisol, some tumours, and rarely the pancreas making too much insulin on its own (an insulinoma).
“Research shows that both high levels and low glucose levels are associated with increased hunger, mood lability, fatigue and sleep impairment...”
Dr Michelle Woolhouse, Vively Medical Director
The symptoms are the same with or without diabetes. The NDSS lists:
Many of these come from adrenaline, which the body releases to push glucose back up. That is why a low can feel like anxiety: a racing heart, sweaty palms and irritability. As glucose falls further, the brain runs short of fuel, and confusion, slurred speech, clumsiness, drowsiness, seizures or loss of consciousness can follow.
Shakiness, sweating and hunger are also common for reasons that have nothing to do with glucose. If you can, check your glucose during symptoms. That one reading tells your GP far more than a description afterwards.
The NDSS steps are written for people with diabetes, and they are a safe approach for anyone with symptoms and a reading under 4.0 mmol/L:
If you have symptoms but no way to check, treat it anyway. If someone is drowsy, confused or unconscious, do not give them food or drink: call triple zero (000).
If you do not have diabetes and lows keep happening, see your GP rather than managing them yourself. A home blood glucose meter lets you capture readings during symptoms.
Short dips under 3.9 mmol/L are common on a continuous glucose monitor (CGM), even in people without diabetes. Across 7,692 Vively members who reported no diabetes, the typical member spent 0.8% of the day below 3.9 mmol/L, about 12 minutes. One in ten spent 4.6% or more, about an hour a day.
The typical member without diabetes spent about 1% of the day under 3.9 mmol/L. Women and younger members logged more low time than men and older members.
% of the day below 3.9 mmol/L, typical (median) member
| Women | Men | |
|---|---|---|
| 18 to 29 | 1.2% (n=449) | 0.5% (n=105) |
| 30 to 39 | 1.1% (n=1,392) | 0.5% (n=555) |
| 40 to 49 | 1.0% (n=1,812) | 0.4% (n=713) |
| 50 to 59 | 0.8% (n=1,379) | 0.5% (n=537) |
| 60+ | 0.7% (n=517) | 0.3% (n=233) |
% of the day below 3.9 mmol/L, member at the 90th percentile
| Women | Men | |
|---|---|---|
| 18 to 29 | 6.8% (n=449) | 3.4% (n=105) |
| 30 to 39 | 5.8% (n=1,392) | 3.8% (n=555) |
| 40 to 49 | 4.7% (n=1,812) | 2.8% (n=713) |
| 50 to 59 | 4.5% (n=1,379) | 3.5% (n=537) |
| 60+ | 3.5% (n=517) | 2.0% (n=233) |
Not every CGM low is real. Sensors measure glucose in the fluid under the skin, not in blood, and lag a few minutes behind. Lying on the sensor at night can squeeze that fluid and show a sudden false drop, called a compression low. CGM consensus targets use 3.9 mmol/L as the low line, which is why our data uses 3.9 rather than 4.0.
If your lows happen mostly overnight, our article on low blood sugar at night explains how to tell a compression low from a real one, and our common CGM mistakes covers sensor placement.
“Currently, a CGM is not a diagnostic tool”
Dr Michelle Woolhouse, Vively Medical Director
This is often a compression low from lying on the sensor. Check whether you slept on that arm, and confirm any low you are worried about with a finger-prick reading.
This fits reactive hypoglycaemia. Try adding protein, fibre and fat to that meal and swapping to lower GI carbohydrates. If the dips come with symptoms, mention them to your GP.
Exercise uses glucose quickly, especially on an empty stomach. Eat a carbohydrate snack before long or hard sessions and refuel afterwards.
Alcohol stops the liver making new glucose. Eat with alcohol, drink less, and have a proper breakfast the next morning.
Treat it with 15 g of fast-acting carbohydrate and see your GP. Lows without an obvious reason need a medical review, and your GP may arrange blood tests during an episode.
See your GP if you do not have diabetes and you have:
Your GP may check your fasting glucose, HbA1c, kidney and liver function and cortisol, and may refer you to an endocrinologist. If you have diabetes and are having frequent hypos, talk to your doctor or diabetes educator about your medicines.
Most people without diabetes can smooth out dips with everyday habits. Eat regular meals that combine protein, fibre and some healthy fat. Swap refined carbohydrates for lower GI options, which raise and lower glucose more gently. Eat when you drink alcohol, and fuel long or hard exercise. Our article on the normal blood glucose range in Australia explains what steady looks like.
If you get shaky or foggy between meals, a CGM can show whether your glucose is dipping at those times, or whether something else is going on. The Vively CGM program pairs the sensor and app with dietitian support through the membership, to help you change meals and timing. The Baseline Health Check measures 70+ markers, including fasting glucose, HbA1c and fasting insulin, read against optimal ranges, with a practitioner to explain your results. Neither replaces your GP for lows that need a diagnosis.
Wear a CGM sensor for 14 days and see how meals, exercise, alcohol and sleep shift your glucose, with dietitian support on what to change.
The common causes are a long gap without food combined with hard exercise, alcohol, reactive hypoglycaemia after a large sugary meal, stomach surgery such as gastric bypass, and medicines. Rarer causes include severe illness, low cortisol and tumours that make insulin. Repeated lows without an obvious reason need a GP review.
The symptoms are the same as in diabetes: shakiness, sweating, hunger, dizziness, headache, trouble concentrating, a tingling face and blurred vision. Severe lows cause confusion, slurred speech, drowsiness, seizures or loss of consciousness. If you can, check your glucose during symptoms so your GP has a reading to work with.
Yes. Feeling weak is one of the NDSS warning signs of a low, along with shaking and trembling. Muscle spasms or cramps are not typical symptoms of low blood sugar and often have other causes, such as dehydration or exercise. If weakness or spasms keep happening, see your GP.
Any reading under 4.0 mmol/L with symptoms should be treated straight away with 15 g of fast-acting carbohydrate. A low becomes an emergency when someone is confused, drowsy, having a seizure or unconscious. Call triple zero (000), and never give food or drink to someone who cannot swallow safely.
Start with 15 g of fast-acting carbohydrate, such as about 6 jellybeans, 150 ml of fruit juice or 3 teaspoons of sugar in water. Check again after 15 minutes. Then have a longer-acting carbohydrate, such as a piece of fruit, a slice of bread or a muesli bar, if your next meal is not soon.
No. CGMs read the fluid under the skin, lag a few minutes behind blood and can show false lows when you lie on the sensor. A sudden overnight drop that bounces straight back is often a compression low. Confirm worrying lows, especially with symptoms, with a finger-prick reading.
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