Blood Sugar Spikes: Myths vs Facts, and Why HbA1c Matters

Short answer: a rise in blood sugar after a meal is normal, and most healthy people don't need a glucose monitor. The number that matters more for your long-term diabetes risk is HbA1c, your average blood sugar over the last two to three months.

Why everyone is talking about blood sugar spikes

Scroll social media and you'll find "glucose hacks", cheese-wrapped grapes and people wearing arm sensors to track every "spike". Online searches for "blood sugar" have risen by more than 30% in five years, and the market for wellness glucose monitors is booming [1].

This month the conversation has two fresh triggers. On 5 November 2026, BBC Science Focus asked nutrition scientists from the University of Oxford and King's College London which blood sugar claims stand up, and several popular ideas did not [1]. And Friday 14 November is World Diabetes Day, which this year focuses on early action: finding diabetes sooner and getting people the right care [2].

In the UK, around 1 in 5 adults has diabetes or prediabetes, and an estimated 1.3 million people may have type 2 diabetes without knowing it [3]. So it's worth separating the hype from the parts that matter.

What is blood sugar, and what is HbA1c?

Blood sugar (glucose) is the main fuel your cells use. After you eat carbohydrates, glucose rises, your pancreas releases insulin, and levels come back down. In type 2 diabetes, insulin doesn't work properly or there isn't enough of it, so glucose stays too high for too long [7].

A finger-prick glucose reading or a glucose monitor shows your level at one moment. HbA1c (glycated haemoglobin) is different. Glucose sticks to haemoglobin in your red blood cells, and because red cells live for around three months, HbA1c reflects your average blood sugar over roughly the previous two to three months.

That makes HbA1c the standard test UK doctors use to spot prediabetes and type 2 diabetes.

These are the thresholds NHS teams use [9]. In the US, prediabetes starts lower, at 39 mmol/mol (5.7%), which is one reason you'll see different numbers online [9], [10].

Blood sugar spikes: myths vs facts

Myth 1: Every glucose spike is damaging

Fact: Blood sugar is meant to rise after a carb-rich meal. Experts interviewed by BBC Science Focus describe this as normal physiology that a healthy body handles well [1]. A US study fitted 153 healthy adults and children with glucose monitors: they spent a median of 96% of the day between 3.9 and 7.8 mmol/L, and only about 30 minutes a day above that [4]. Problems are linked to blood sugar that stays high, repeatedly, over months and years.

Myth 2: Spikes cause harmful inflammation

Fact: There is a short, mild immune response after eating, and that is normal too. The concern is with repeated, very high rises over long periods, which is what happens in poorly controlled diabetes [1].

Myth 3: Your afternoon slump is a blood sugar crash

Fact: Sometimes a dip plays a part, but sleep, stress and your body clock matter at least as much. Healthy bodies switch smoothly between glucose and fat for fuel [1].

Myth 4: Everyone should wear a glucose monitor

Fact: Continuous glucose monitors (CGMs) are valuable for many people with diabetes. For people without diabetes, a 2024 review of 25 studies led by UCL found no consistent, high-quality evidence of benefit, little data on how accurate the devices are in this group, and a risk of anxiety about food [5].

Myth 5: Eating sugar causes type 2 diabetes

Fact: Sugar on its own isn't the direct cause. The main drivers are excess calories leading to weight gain (especially around the waist), inactivity, age, family history and ethnic background [6]. Sugary drinks and foods can make weight gain easier, so cutting back still helps.

Myth 6: Slim people don't get type 2 diabetes

Fact: Weight is a big risk factor but not the only one. Around 10% of adults aged 16 to 54 with type 2 diabetes are not overweight [6].

Myth 7: You'd know if your blood sugar was too high

Fact: Prediabetes usually has no symptoms, and early type 2 diabetes often doesn't either [7], [8]. That's why a blood test, not how you feel, is the way to find out.

Prediabetes: who's at risk and when to see a GP

Prediabetes means your blood sugar is higher than normal but not yet in the diabetes range. An estimated 6.3 million people in the UK have it [3]. Each year, roughly 5 to 10% of people with prediabetes go on to develop type 2 diabetes, and a similar share return to normal [9].

Who is more likely to have high blood sugar

The NHS lists these as higher-risk groups [7]:

• White people over 40, or people over 25 from South Asian, Chinese, Black African or Black Caribbean backgrounds
• Anyone with a parent, brother or sister with type 2 diabetes
• People who are overweight and not very active
• People with related conditions such as high blood pressure

Diabetes UK's free Know Your Risk tool estimates your 10-year risk in a few minutes using your height, weight and waist size [8].

Warning signs of type 2 diabetes

See your GP if you notice [7]:

• Feeling very tired
• Peeing more than usual, especially at night
• Feeling thirsty all the time
• Losing weight without trying
• Blurred vision, cuts that heal slowly, or genital itching or repeated thrush

The NHS also advises getting checked if you're in a higher-risk group, even without symptoms, because not everyone has them [7]. If you feel very unwell, are vomiting, breathing fast or are drowsy, get urgent medical help rather than waiting for a test.

What actually lowers your risk (no gadgets needed)

The evidence points to steady habits, not hacks.

• Weight loss, if you have weight to lose. Weight gain is the main driver of insulin resistance and type 2 diabetes, and losing weight improves both [1], [13].
• Moving more, including short walks after meals [13].
• More fibre, fewer refined carbs and sugary drinks, with sensible portions [13].
• Regular sleep. In one small study, pushing bedtime 90 minutes later for six weeks made insulin work less well in healthy women [13].

Pairing carbs with protein, fat or fibre can help people who already have prediabetes or diabetes, but experts say it's mostly unnecessary for everyone else and can add calories [1].

The NHS Diabetes Prevention Programme

If a GP blood test shows prediabetes (HbA1c 42 to 47 mmol/mol), adults in England can be referred to the free NHS Diabetes Prevention Programme, a 9-month lifestyle course [9]. A study of more than 69,000 people found those referred were 20% less likely to develop type 2 diabetes over three years than similar people who weren't [11]. People with prediabetes are also advised to have their HbA1c rechecked every year [15].

Can prediabetes be reversed?

It can be. Returning to normal blood sugar is sometimes called prediabetes "remission". In a long-term analysis of two large prevention trials, people who reached remission had about half the risk of dying from heart disease or being admitted with heart failure over the following decades [12]. This was not a randomised comparison, and only around 1 in 10 people reached remission, but it suggests acting early is worthwhile.

How to check your HbA1c at home with LHC

If you'd like to know where you stand, our HbA1c Blood Test Kit lets you collect a small finger-prick sample at home and post it back in the prepaid envelope. It's analysed by HPLC in our CQC-regulated UK laboratory, and you get a numerical PDF report you can share with your GP.

Good to know before you test

• HbA1c reflects the last two to three months, so you don't need to fast. Follow the timing and posting instructions in your kit.
• One result is a snapshot of your risk, not a diagnosis. Diabetes is diagnosed by a doctor, usually with a repeat test.
• HbA1c can read falsely high or low in some situations: pregnancy, sickle cell trait, thalassaemia and other haemoglobin variants, some types of anaemia, recent blood loss or transfusion, advanced kidney disease, after spleen removal, and with certain medicines [14]. If any apply to you, speak to your GP, who may use a glucose test instead.
• HbA1c isn't the right test for suspected type 1 diabetes or symptoms that came on quickly. If you have the warning signs above, see a doctor rather than waiting for a home test.

What to do with your result

• Below 42 mmol/mol: keep up healthy habits; retest if your risk changes.
• 42 to 47 mmol/mol: book a GP appointment to confirm it and ask about the NHS Diabetes Prevention Programme.
• 48 mmol/mol or above: contact your GP promptly so they can repeat the test and advise you.

Already have a result? Our guide What Does My HbA1c Result Mean? explains the numbers in more detail.

Recent research and what's next

• Where to draw the prediabetes line. A 2026 systematic review concluded HbA1c below the diabetes threshold is best read as a sliding scale of risk rather than a yes/no label. Results of 6.0 to 6.4% (42 to 47 mmol/mol) pick out people at higher near-term risk, while the wider US range of 5.7 to 6.4% catches more people at lower risk [10].
• Remission matters. The 2025 Lancet Diabetes & Endocrinology analysis linking prediabetes remission to fewer heart deaths [12] has prompted calls for trials testing which approaches, including newer weight-loss medicines, work best for whom.
• Glucose monitors for healthy people. Researchers are calling for better regulation, an accuracy standard and more research on how wellness CGM users are affected [5].

The takeaway for World Diabetes Day: forget chasing every spike. Know your risk, check your HbA1c if you're in a higher-risk group, and act early if it's creeping up.

References

1. Willmoth H. We've been thinking about blood sugar all wrong. Here's why. BBC Science Focus, 5 November 2026.
2. World Health Organization. World Diabetes Day 2026: early action on diabetes.
3. Diabetes UK. One in five adults now live with diabetes or prediabetes in the UK. 6 February 2025.
4. Shah VN, et al. Continuous glucose monitoring profiles in healthy nondiabetic participants: a multicenter prospective study. Journal of Clinical Endocrinology & Metabolism, 2019.
5. UCL News. Use of glucose monitors by people not living with diabetes needs more regulation (review in Diabetic Medicine). 27 June 2024.
6. Davis A, reviewed by Jarvis S. What are the common myths surrounding type 1 and type 2 diabetes? Patient.info.
7. NHS. Type 2 diabetes: symptoms. Last reviewed 10 February 2025.
8. Diabetes UK. Prediabetes symptoms. Last reviewed 27 January 2026.
9. Morris D. Prediabetes (non-diabetic hyperglycaemia). Independent Nurse, March 2024.
10. Karczewski D, Karczewski T, Olsen M. Glycated haemoglobin and prediabetes: a systematic review of HbA1c thresholds for type 2 diabetes prevention. Journal of Clinical Medicine, 2026;15(12):4690.
11. NIHR Evidence. How effective are referrals to the NHS Diabetes Prevention Programme? Summary of Ravindrarajah R, et al. PLoS Medicine, 2023.
12. Arreola EV, et al. Prediabetes remission and cardiovascular morbidity and mortality: post-hoc analyses from the DPPOS and DaQing studies. The Lancet Diabetes & Endocrinology, 2025. As reported by TCTMD, 19 December 2025.
13. Ong S. The surprising real cause of prediabetes (and how to reverse it). BBC Science Focus, 3 October 2026.
14. North Midlands and Cheshire Pathology Service. HbA1c for diagnosis of diabetes mellitus. November 2025.
15. NHS Bristol, North Somerset and South Gloucestershire ICB. Non-diabetic hyperglycaemia and the National Diabetes Prevention Programme.

This article is for general information and isn't a substitute for medical advice. A home test can't diagnose diabetes; speak to your GP about symptoms or results.