Type 3 Diabetes - Insulin resistance and Alzheimer’s Disease
When you think about Alzheimer's Disease (AD), you probably picture someone in their 70s or 80s struggling with memory loss. But here's the sobering reality that keeps me up at night as a metabolic health specialist - the disease process starts decades earlier, quietly accumulating damage long before lost memories.
Research from the National Institute on Aging confirms that changes in the brain may begin a decade or more before symptoms appear, with toxic protein buildups occurring during this very early stage. One of the causes in some cases? Insulin resistance. Yep, the connection has led some to call AD “Type 3 Diabetes”.
Even more striking, Johns Hopkins researchers identified brain changes linked to AD that occur three to 10 years (some even more than 30 years) before the first recognizable symptoms.
Think about that. Thirty years. The brain pathology that will eventually steal someone's memories, their independence, their very sense of self - it's already setting up shop while they're in the prime of their life, crushing it at work, raising kids, planning for retirement.
What’s Actually Happening in the Brain in AD?
If you’ve learned about AD, you may be familiar with the terms “plaques” and “tangles” to describe two physical changes that happen in the nerves of the brain over the years of the disease. While genetics plays a role in how susceptible someone is to these plaques and tangles, environmental factors (read: lifestyle changes) can impact how much susceptible someone is to showing signs of AD.
The brain loves using glucose as fuel - to the tune of 120-130 grams per day (WOW!!). The brain doesn’t have a sweet tooth - it’s just how those neurons are programmed to operate. (Small note: this doesn’t have to be the glucose that’s straight from a can of soda. It could be a very nourishing complex carbohydrate, like a sweet potato or beans, broken down into its little glucose sugars.)
But, the glucose can’t cross over the cell membrane into the neurons by itself. The glucose molecule is too big, too complicated - it needs an escort to let it in. That’s where insulin comes in. However, if the insulin isn’t doing a good job (insulin resistance), the neurons can’t get their favorite glucose. And if they can’t get their favorite glucose, they aren’t as able to keep themselves clean or do their jobs. In fact, some studies showed that administration of insulin improved memory.
So, with insulin resistance comes more plaques and more tangles.
The Invisible Timeline
As we discussed in our post about making your golden years truly golden, Americans are living longer than ever, with 87 being the most common age people reach. But longevity without quality is just extended time on the clock. The average person is diagnosed with type 2 diabetes at 45, meaning they've already been living with metabolic dysfunction for potentially 17 years by retirement age.
Now layer AD on top of that timeline. Hallmarks of AD, such as amyloid buildup, may be present up to 20 years before someone exhibits changes in memory, thinking or behavior. This isn't some distant threat for "old people." This is happening in people in their 40s, 50s, and 60s who feel perfectly fine.
The disease progression is insidious. Beta-amyloid plaques and tau tangles begin accumulating silently. The hippocampus - your brain's memory center - starts taking hits. But you won't notice. Not yet. By the time symptoms appear, significant irreversible damage has already occurred.
Prevention: The Biggest Game in Town
Here's the uncomfortable truth: we don't have a cure for AD. We have some medications that may slow progression in early stages, but nothing that reverses the damage. That's why prevention isn't just important - it's everything.
The good news? Nearly half of AD cases could have been prevented or delayed by modifiable lifestyle factors. Let that sink in. We're not powerless here. The choices you make today are literally determining your brain's future trajectory.
As we explored in our body and mind post, the relationship between lifestyle factors and metabolic health is profound. Sleep, stress, physical activity - they're all interconnected pieces of the brain health puzzle. And the stakes couldn't be higher.
Move Your Body, Save Your Brain
Low levels of physical activity are a risk factor associated with AD disease, while older adults who exercise are more likely to maintain cognition. The research here is absolutely compelling.
A groundbreaking study published in Nature Medicine found something remarkable: cognitive decline was delayed by three years on average for people who walked just 3,000 to 5,000 steps per day, and by seven years in people who walked 5,000 to 7,500 steps per day. Seven years of preserved cognition from a moderate daily walk. That's not a pharmaceutical intervention requiring prior authorization and costing thousands. That's free. That's accessible to almost everyone.
The mechanism matters too. Higher physical activity was associated with slower amyloid-related tau accumulation, which significantly mediated the association with slower cognitive decline. Exercise isn't just generally "good for you" (it's directly interfering with the pathological processes that drive AD disease).
Exercise modulates amyloid beta turnover, inflammation, synthesis and release of neurotrophins (essentially hitting multiple protective mechanisms simultaneously). Research suggests that moderate-intensity aerobic exercise combined with resistance training may be particularly effective, as each type triggers different beneficial brain changes.
Finally, it’s vital to connect activity and insulin resistance, and I couldn’t have said it any better way, so I’ll include an excerpt here:
“A decrease in muscle mass is an important cause of the gradual increase in insulin resistance associated with age. This is because skeletal muscles are the main glucose absorbers in response to insulin, and when muscle mass decreases, blood glucose drops less, which leads to increased insulin resistance.”
Even modest amounts make a difference. Engaging in as little as 35 minutes of moderate to vigorous physical activity per week was associated with a 41% lower risk of developing dementia. For people who think they're too busy or too out of shape to make a difference (you're not). Every bit helps.
Sleep: Your Brain's Nightly Maintenance Crew
Remember our discussion about the 42 factors affecting blood glucose? Sleep was a major player. It's equally critical for Alzheimer's prevention, and the mechanisms are fascinating.
During deep sleep (specifically non-REM slow-wave sleep) your brain essentially runs a cleaning cycle. When we sleep, brain cells and their connections actually shrink, allowing more space between brain cells so that beta amyloid and other substances that accumulate during the day can be flushed away. Skip that deep sleep consistently, and those toxic proteins just keep accumulating.
The data is stark. Research from the Framingham Heart Study found that as little as a 1 percent decrease in the amount of time spent in deep sleep each night translates to a 27 percent increase in the risk of dementia. One percent. That's the margin we're working with.
And this isn't just about people already showing symptoms. Research found that consistently sleeping six hours or less at age 50, 60, and 70 was associated with a 30% increase in dementia risk. The mean age of diagnosis was 77 years - meaning inadequate sleep in midlife was predicting brain health decades later.
But here's an encouraging finding: superior amounts of deep, slow-wave sleep can act as a protective factor against memory decline in those with existing high amounts of Alzheimer's disease pathology. Even if pathological changes have already started, quality sleep may help buffer against their worst effects. Think of deep sleep as a life raft keeping memory afloat despite the weight of disease pathology.
The Integration: Why Everything Connects
As we covered in our Project Brain Food post, brain health isn't a single-factor equation. Your brain accounts for only 2% of your body weight but demands 20% of your body's energy. Fuel it poorly, stress it chronically, deprive it of quality sleep, keep it sedentary - and you're essentially running mission-critical software on a dying battery.
The metabolic connection matters profoundly. Poor sleep impairs insulin sensitivity. Physical inactivity promotes inflammation and drives insulin resistance. Chronic stress drives cortisol dysregulation. These aren't separate issues - they're interconnected pathways all converging on brain health.
And we're not just talking about AD in isolation. Type 2 diabetes, cardiovascular disease, chronic inflammation - they're all part of the same metabolic dysfunction that accelerates cognitive decline.
What This Means, Right Now
So here we are. Brain changes linked to AD can start 20-30 years before symptoms. Prevention is possible through modifiable lifestyle factors. Exercise and sleep are two of the most powerful interventions we have. And yet most people don't think about brain health until they're already experiencing problems.
The best time to start protecting your brain was 20 years ago. The second best time is today.
This isn't about perfection. It's about nudges. Can you add 2,000 more steps to your daily routine? Can you prioritize 7-8 hours of sleep instead of making do with 5-6? Can you address the chronic stress that's quietly activating fight-or-flight responses dozens of times per day?
These aren't theoretical interventions for some distant future version of yourself. These are practical strategies that protect your brain starting immediately. Every walk counts. Every night of quality sleep matters. Every stress management technique you implement has compound benefits.
As we always say at The Signature Plate: addressing root causes requires support. Working with a metabolic health specialist can help you implement evidence-based strategies systematically rather than just hoping for the best. When it comes to brain health, hope isn't a strategy - but action is.
Your 90-year-old self is counting on the choices you make today. Let’s make them proud.
