Sugar, Metabolic Syndrome and Early-Onset Dementia: Is This Type 3 Diabetes?

Why are more people in their 40s and 50s developing dementia? Most assume the answer lies in the genes. But here’s the reality: fewer than 1% of Alzheimer’s cases are caused by rare genetic mutations. The other 99%? They are driven largely by preventable, lifestyle-related factors – and at the centre of the storm is how we process sugar, , leading many scientists to describe Alzheimer’s as “Type 3 diabetes.”

A major new study of nearly two million people confirms that metabolic syndrome – the cluster of blood sugar imbalance, abdominal obesity, high blood pressure, and poor lipid levels  – significantly increases the risk of early-onset dementia.

This should be front-page news. Dementia is now affecting people in their 40s and 50s, not just the elderly. And at the heart of this early decline? Poor blood sugar control, excess abdominal fat, and the metabolic mayhem caused by high-sugar diets.

The Evidence: 24% Higher Risk of Dementia Before Age 65

The landmark 2024 study published in JAMA Neurology followed more than 1.9 million adults and found that those with metabolic syndrome had a 24% higher risk of developing dementia before the age of 65 compared with those without (1).

The strongest associations were observed with:

Hyperglycaemia (high blood sugar)
Abdominal obesity (visceral fat around the waist)

These two factors, when present together, were particularly predictive of vascular dementia, although risks were also elevated for Alzheimer’s disease and other forms of dementia.

The authors adjusted for other lifestyle and demographic factors, confirming that metabolic health itself was an independent driver. Men and those in their 40s showed the highest vulnerability.This aligns with decades of research linking insulin resistance and poor glucose control with brain shrinkage, memory loss, and neurodegeneration – all of which are discussed in detail in [here] and [here]. 

The Type 3 Diabetes Hypothesis

Scientists have increasingly referred to Alzheimer’s disease as “Type 3 diabetes” – a term that reflects how brain cells become resistant to insulin and fail to metabolise glucose properly.

Chronically high blood sugar damages blood vessels in the brain, increases inflammation, and accelerates the formation of amyloid plaques, all hallmark features of Alzheimer’s pathology. This new study provides the strongest population-level evidence to date that the same dysfunction is also driving younger-onset dementia.

The Role of Fructose and Processed Sugar

Endocrinologist and paediatric neuroendocrinologist Dr Robert Lustig has long warned of the unique effects of fructose (a sugar found in high-fructose corn syrup and added sugars) on the brain. Unlike glucose, fructose is processed in the liver, promoting visceral fat, insulin resistance, and inflammation – all central to metabolic syndrome (2).

When the brain is chronically exposed to excess sugar and insulin, its ability to generate energy and form new synapses becomes impaired. Over time, it is as if the brain is being starved, even in the midst of plenty.

 This isn’t just a long-term risk – we’re now seeing it play out in middle-aged adults.

Thankfully we know that there is much you can do to prevent this from happening – your future is in your hands – here is what to focus on.

What Can You Do? Five Simple Shifts

Check your blood sugar regulation. The HbA1c test is a key marker of long-term blood glucose control. (Available via our home test kits and in our DRIfT 5 in 1 test kit.)
Prioritise low-GL, whole foods. Swap out refined carbohydrates and processed sugars for whole grains, legumes, nuts, and non-starchy vegetables.
Limit fructose. Reduce or remove sweetened drinks (including fruit juice), syrups, and processed snacks high in high-fructose corn syrup. Read more on high/low fructose foods here.
Assess your waist size. Abdominal fat is a strong dementia risk factor. A healthy waistline helps protect your brain.
Exercise regularly. Just 30 minutes a day improves insulin sensitivity and helps the brain use glucose more efficiently.

Need help taking action on the above? Struggle to know how to ditch your sweet tooth?

Join us in the Forget Sugar Webinar in October with Patrick Holford.

A Wake-Up Call, Not a Life Sentence

This study shows a sobering trend – but Food for the Brain exists to empower you in your prevention path. Early-onset dementia is not inevitable. It is largely preventable if you act now. Sugar, insulin resistance, and metabolic syndrome are right at the centre of the problem.

We need public health messaging that reflects this. Dementia is not just an age-related disease. It’s a lifestyle-driven brain disorder that begins years, even decades, before diagnosis.

Your brain doesn’t have to retire early – start your brain upgrade programme and journey today.Want to assess your brain health? Complete this free validated online Cognitive Function test to receive personalised insights into your brain health, along with guidance on what you can do to reduce your risk and protect your future!

Food for the Brain is a not-for-profit educational and research charity that offers a free Cognitive Function Test and assesses your Dementia Risk Index to be able to advise you on how to dementia-proof your diet and lifestyle.

By completing the Cognitive Function Test you are joining our grassroots research initiative to find out what really works for preventing cognitive decline. We share our ongoing research results with you to help you make brain-friendly choices.

Please support our research by becoming a Friend of Food for the Brain.

References

 Jang H et al. Association Between Metabolic Syndrome and Early-Onset Dementia in a Nationwide Cohort. JAMA Neurol. 2024. doi:10.1001/jamaneurol.2024.xxxxxx
Lustig RH. Fat Chance: The Hidden Truth About Sugar, Obesity and Disease. Penguin; 2013.https://pubmed.ncbi.nlm.nih.gov/12450889/