The Truth About the 'Sugar' That Erodes the Brain.

To keep dementia at bay and
things you should know to keep a 'sharp mind' for life.

"I've been forgetting things more often lately,"
"I can't recall people's names right away,"
"I can't maintain my concentration,"
"My brain gets tired more easily than it used to."

As we age through our 40s, 50s, and 60s, it is not uncommon for people to feel these kinds of changes.

And what many people worry about is, "Will I develop dementia in the future?"

In fact, dementia is no longer considered a "disease that suddenly begins after you get old."

It is known that in Alzheimer's disease, changes such as amyloid-beta begin in the brain more than 10 years, and in some cases more than 20 years, before symptoms appear.
The U.S. National Institute on Aging (NIA) also explains that it can take more than 20 years from the start of amyloid accumulation until symptoms appear.

In other words, "taking measures against dementia starting in your 60s" might be too late.
We need to think about blood sugar, blood pressure, exercise, sleep, diet, and human connections from an even earlier stage. Among these, this time we will consider the relationship between "sugar" and the brain.

※This will be a slightly long article.

・To begin with, how common is dementia in Japan?

First, let's look at the numbers.
According to estimates by a research team from the Ministry of Health, Labour and Welfare, as of 2022, there were approximately 4.43 million people with dementia aged 65 and older.
That is about 12.3% of the population aged 65 and older, or roughly one in eight people.
Furthermore, it is estimated that there are approximately 5.58 million people with mild cognitive impairment (MCI), which is considered the stage before developing dementia.

In other words, dementia: approximately 4.43 million people, MCI: approximately 5.58 million people.
Combined, this reaches a scale of approximately 10 million people. On the other hand, estimates have also been published that the number of people with dementia will reach approximately 5.84 million in 2040.

This is by no means just an "issue for the elderly."
Rather, it is an issue of what will happen in the future to people who are currently in their 40s and 50s.

・Why are "diabetes" and "dementia" related?

What becomes important here is the relationship between diabetes and dementia.
Diabetes is not simply a "disease of high blood sugar."
If a state of poor blood sugar control continues over a long period, it affects the entire body, including blood vessels, nerves, kidneys, eyes, and the heart.
And the brain is no exception.

Diabetes is established as one of the risk factors for dementia, and in the 2024 Lancet Commission, diabetes is listed as one of the modifiable dementia risk factors throughout life.
In other words, "managing blood sugar" is also important when thinking about brain health.

・One must be careful with the term "Type 3 diabetes"

When explaining the relationship between Alzheimer's disease and insulin resistance, the expression "Alzheimer's disease is Type 3 diabetes" is sometimes used.
This is a concept born from research showing that abnormalities in insulin signaling and sugar metabolism also occur in the brain.
In fact, there are numerous studies on the relationship between insulin resistance, oxidative stress, inflammation, amyloid-beta, tau, and so on.

However, "Alzheimer's disease = diabetes" is not the case.
"Type 3 diabetes" is not an official diagnostic name, but a term used as a hypothesis or concept in research.
Various factors are involved in Alzheimer's disease, including genetics, aging, blood vessels, metabolism, inflammation, lifestyle habits, and the environment.
That is precisely why it is not a simple story of "if you don't eat sugar, you won't get dementia."

🍰 The problem is not "sugar itself," but the disruption of sugar metabolism

This is the most important point this time.
Our brains need energy.
And usually, one of the main sources of that energy is glucose.
In other words, sugar is not evil.

The problem is "consuming more than necessary" and "having blood sugar levels remain high for a long period."
Furthermore, when obesity, visceral fat, insulin resistance, high blood pressure, and lipid abnormalities overlap, it affects the health of the entire body, including the cerebral blood vessels.

In other words, rather than "eating something sweet once," we need to look at the accumulation of lifestyle habits over years and decades.

🧠 Brain changes begin "20 years before symptoms appear."

This is extremely important when thinking about dementia prevention.
The accumulation of amyloid-beta in Alzheimer's disease can begin quite a long time before symptoms appear.
In research introduced by the NIA, it is shown that it may take more than 20 years from the start of amyloid accumulation until symptoms appear.

In other words, even if there is a person who started having memory lapses at age 60, the brain changes themselves may have started around age 40 or even earlier.
That is why "I'm still in my 40s, so I'm fine" is not true.
Rather, your 40s and 50s are the important time to think about the future of your brain.

🍩 "If you eat something sweet, your brain will be destroyed" is a mistake

There is something you must not misunderstand here.
Eating cake, eating ice cream, eating ramen—that alone will not cause Alzheimer's disease.
Also, there is no scientific basis that "you can prevent dementia if you completely cut out carbohydrates."

What is important is not to make carbohydrates zero, but to keep blood sugar metabolism in good condition.
To do that, you need to look at your entire lifestyle—not making sweet drinks a habit, not snacking mindlessly, consuming dietary fiber, ensuring protein intake, maintaining a proper weight, exercising, and so on.

🚶 The option of 10 minutes of exercise after a meal

What is interesting for blood sugar measures is walking after a meal.
In a randomized crossover trial published in 2025, 12 healthy young adults were compared under conditions such as walking for 10 minutes immediately after consuming 75g of glucose.

Due to the 10-minute walk, the 2-hour area under the blood glucose curve (AUC) and the average blood glucose level were lower than in the resting condition.
The peak blood glucose level was also approximately 181.9 mg/dL at rest and approximately 164.3 mg/dL with a 10-minute walk, a result that was approximately 9.7% lower.

Of course, this is not a study that says "if you walk for 10 minutes, you can prevent dementia."
However, it is data showing that a small habit of walking a little after a meal can be useful for blood sugar control. You don't have to buy expensive health equipment; just walk for 10 minutes after a meal.
This is something you can do starting today.

🦵 What about "heel raises"?

Even while sitting, you can incorporate light exercise like "heel raises."
Moving the muscles around the calves leads to promoting the use of sugar by the muscles.

However, expressions like "if you move your soleus muscle, diabetes will be cured" or "heel raises are the strongest exercise for dementia prevention" are exaggerations.
What is important is to reduce sitting all the time and to move your body on a daily basis. This is it.

🏃 "Exercise" can become medicine for the brain

In the 2024 Lancet Commission, modifiable factors related to dementia risk were organized into 14 items.
These include diabetes, high blood pressure, obesity, physical inactivity, smoking, excessive alcohol consumption, high LDL cholesterol, hearing loss, depression, social isolation, air pollution, traumatic brain injury, vision loss, and education.

The Lancet Commission estimates that by improving these 14 factors, up to 45% of dementia cases worldwide could potentially be prevented or delayed.

What is important here is "not to look only at sugar." Dementia prevention is not just about blood sugar.
Blood pressure, cholesterol, exercise, sleep, hearing, and human connections too.
Everything is connected.

😴 Is the brain "cleaning" itself while sleeping?

There is also very interesting research regarding sleep. The brain has a mechanism called the glymphatic system, which is thought to be related to the discharge of waste products in the brain.
In recent human studies, data has emerged showing that clearance of amyloid-beta, tau, and other substances by this system is promoted during normal sleep.

In a randomized crossover trial of 39 people published in 2026, normal sleep and sleep deprivation were compared, and it was shown that glymphatic clearance during sleep is related to the movement of Alzheimer's-related biomarkers.

In other words, it means that the brain is not just resting while you are asleep.
However, it is not a simple story that "if you sleep for 6-8 hours, amyloid-beta will be completely washed away."
Not only sleep duration, but sleep quality, sleep disorders, and lifestyle rhythms are also important.

📚 "Using your head" is also related to brain health

This is the interesting part.
When people talk about dementia prevention, their eyes tend to focus only on "reducing sugar" and "exercising."
However, using the brain itself is also important.

Reading, musical instruments, shogi, go, language learning, travel, new work, conversation with people, dancing.
These activities do not just "use your head."
Memory, attention, judgment, movement, communication—you use multiple brain functions at the same time.

In a meta-analysis covering 38 studies and approximately 2.15 million people, physical activity, cognitive activity, and social activity were all associated with a decrease in the incidence of dementia.
Especially in cognitive activity, RR 0.77—in other words, in research, an association has been confirmed that people with more cognitive activity have less incidence of dementia.

However, this also mainly summarizes observational studies, and it is not something that can be asserted as "if you read, you won't get dementia."

🤝 In fact, "conversation with people" also works for the brain

What is even more interesting is social connection.
In a meta-analysis summarizing 32 studies, people with strong social engagement had a lower risk of dementia, with an RR of 0.81.
For frequent social contact, the RR was 0.86.
On the other hand, regarding feelings of loneliness, an association with an increased risk of dementia was reported, with an RR of 1.42.

In other words, not just "eating health food alone," but talking to people, laughing, going out, eating with someone—these actions cannot be ignored from the perspective of brain health.

🧠 And, the "cognitive reserve" that must not be forgotten

There is a very interesting way of thinking in Alzheimer's disease research.
That is cognitive reserve.
Even if there is the same degree of brain pathology, there are "people whose symptoms appear strongly" and "people whose cognitive function is maintained surprisingly well."
A concept that explains part of that difference is cognitive reserve.

Education, work, reading, intellectual activity, social activity, new experiences.
Through the accumulation of these experiences, the brain has multiple routes.
That is the image.
Therefore, "continuing to use your brain" has meaning.

🍰 So, what should you change starting today?

You don't need to do anything difficult.
First, these five things.

① Reduce sweet drinks
Juice, soft drinks, coffee with sugar, etc., are liquids, so it is easy to consume excessive sugar.
Start with "drinks are sugar-free."

② Reduce mindless snacking
Avoid the state of "eating all day without realizing it" by eating small amounts of snacks.
Make a clear distinction between meals and snacks.

③ Walk for 10 minutes after a meal
Especially on days when you "ate a lot of carbohydrates," walk a little after the meal.
Even just 10 minutes can potentially affect your blood sugar response.

④ Sleep well
Sleep is not "time spent doing nothing."
It is an important time related to brain recovery and metabolism.

⑤ Talk to someone every day
Family, friends, work colleagues, shop staff, neighbors.
Online is fine too.
Make "connecting with people" a habit.

"Not fearing sugar," but "controlling sugar"

The brain needs energy.
The problem is not sugar itself, but the disruption of metabolism over a long period.

Therefore, rather than extreme methods like zero carbohydrates, completely cutting out carbohydrates, or completely banning sweets, it is important to "continue a lifestyle that does not easily disrupt blood sugar for a long time."

And, the biggest point

What the 2024 Lancet Commission showed is that dementia is not just a "disease that cannot be helped because it is genetic."
Combined, the 14 modifiable risk factors mean that up to 45% of dementia cases worldwide could potentially be prevented or delayed.

Of course, this does not mean that "45% of people will definitely not get dementia,"
nor does it mean that each individual's risk will decrease by 45%.
However, we know that the idea that "there is nothing I can do" is wrong.

🧠 "The brain 20 years from now" is being made today

Dementia symptoms might appear in your 60s, 70s, or 80s.
But brain changes may have started long before that.

Therefore, your diet in your 40s, exercise in your 40s, sleep in your 40s, relationships in your 40s, blood pressure in your 40s, and blood sugar in your 40s.
These are "advance investments" in yourself 20 years from now.

Finally

When people talk about dementia prevention, they tend to think, "I have to do brain training," "I have to take supplements," or "I have to eat this food."
But what is really important is simpler.

Don't overeat.
Don't make sweet drinks a habit.
Move your body.
Sleep well.
Manage blood pressure, blood sugar, and cholesterol.
Use your head.
Talk to people.
And continue this for many years.

Dementia is not just a disease where "the brain suddenly breaks one day."
Over a long period of time, various factors such as the body's metabolism, blood vessels, inflammation, sleep, exercise, connection with society, and intellectual activity accumulate.
Instead of "completely cutting off sugar," try starting a "lifestyle of getting along well with sugar."

That may be the realistic first step to living with a "sharp mind" for life.
📌

Numbers to remember from this article- 4.43 million → Estimated number of people with dementia aged 65 and older in Japan in 2022

- Approximately 12.3% → Percentage of dementia among those aged 65 and older in 2022
- Approximately 5.84 million → Estimate of the number of people with dementia in 2040
- More than 20 years → Sometimes shown as the period from the start of amyloid accumulation to the appearance of Alzheimer's symptoms
- 45% → The percentage estimated by the 2024 Lancet Commission that could potentially be prevented or delayed by taking measures against 14 modifiable risk factors
- 10 minutes → Even a 10-minute walk after a meal was confirmed to have the effect of suppressing the rise in postprandial blood sugar in experimental conditions
- 81% → In a meta-analysis investigating social engagement and dementia risk, the RR for strong social engagement was 0.81. It does not mean that 81% of diabetic patients were dementia patients
※In this article, expressions such as "sugar toxicity" and "Type 3 diabetes" are treated not as medically established diagnostic names or disease names, but as metaphors and research concepts explaining the relationship between sugar metabolism abnormalities and Alzheimer's disease.

Also, there is no scientific basis that dementia can be prevented solely by carbohydrate restriction or specific foods.
It is important to think about dementia risk from multiple factors, not just blood sugar, but also blood pressure, LDL cholesterol, exercise, smoking, alcohol consumption, hearing, vision, and social connections.