People are living longer these days, with the average life expectancy for people in the U.S. reaching 80.7 years for women and 74.1 for men, according to a scientific study published in JAMA.

Yet unfortunately, for many people, their later years are not spent in good health.

According to the same study, the U.S. has the largest gap between healthspan (the number of years one spends in good health) and lifespan (the number of years one lives).

Dementia is one of the biggest threats to healthspan. According to the National Institutes of Health, researchers estimate that 42% of Americans over 55 will eventually develop dementia.

Ready for some good news? You can control your brain health more than you probably think.

A 2024 report published in The Lancet says that an estimated 45% of dementia cases are preventable through diet and lifestyle habits.

Certainly, it’s our everyday habits that impact our health the most, including our brain health. There’s one common habit in particular that brain health experts we talked to said could be increasing one’s dementia risk without them even realising it.

When the afternoon munchies hit, what do you reach for? If it’s something sugary, you could be increasing your risk of dementia.

According to brain health experts we talked to, there is a wealth of scientific research showing a connection between a high-sugar diet and increased dementia risk, particularly when something sugary is eaten in the afternoon.

Julie Andrews, a registered dietitian specialising in the MIND diet (an eating plan created to lower dementia risk) and the author of The MIND Diet Plan and Cookbook, shared that one reason for the link between a high-sugar diet and dementia risk is that sugary foods spike blood sugar levels.

“Studies show large variations in blood glucose levels over a long period of time – both highs and lows – can increase dementia risk because it can damage blood vessels in the brain, cause inflammation in the body and starve brain cells of the fuel they need to function properly. This can impact everyone, not just those with diabetes,” Andrews said.

Dr Alvaro Pascual-Leone, a professor of neurology at Harvard Medical School and the chief medical officer at Linus Health, also told HuffPost that having chronically unstable blood sugar levels can negatively impact the brain.

“Insulin regulation is not just important for metabolism. It’s also important for the brain itself,” he said. He explained that a high-sugar diet can lead to brain insulin resistance, which is when the brain cells can’t use glucose properly. This can lead to memory loss and dementia. Pascual-Leone shared that this is unofficially being referred to as type 3 diabetes.

“Unstable or high blood sugar may contribute to damaging blood vessels, including the tiny ones that feed the brain. It’s linked to oxidative stress, which can injure brain cells. It may also interfere with how brain cells use energy, since glucose is the brain’s main fuel,” said Dr Dung Trinh, the chief medical officer of Healthy Brain Clinic and an internist with MemorialCare Medical Group in Irvine, California.

Besides raising blood sugar, MIND Diet for Beginners author and registered dietitian Kelli McGrane told HuffPost that sugar also impacts the brain’s reward system.

“One reason sugar is so appealing is that it triggers dopamine release in the brain’s reward pathway. While occasional or moderate intake isn’t typically concerning, consistently high sugar intake can overstimulate this system. Over time, this may negatively affect learning, memory, mood regulation and even motivation,” she said.

Afternoon blood sugar spikes are especially bad for brain health, Pascual-Leone said. He explained that this is because glucose intolerance is naturally lower in the later half of the day compared to the morning, making blood sugar spikes from sugary snacks even more dramatic.

Andrews and Pascual-Leone both told HuffPost that another reason why eating something high in sugar later in the day is particularly detrimental is that it can get in the way of sleeping well. Tringh said this too, pointing out that sugar can impact sleep, and consistently not getting enough sleep increases the risk of dementia.

Pascual-Leone explained that sleep is crucial for protecting against dementia because it’s when the brain clears out neurotoxic proteins. If these toxic proteins (specifically ones named beta-amyloid and tau) aren’t cleared out, he said, they can interfere with communication between neurons. Scientific research shows a clear connection between beta-amyloid and tau accumulation and dementia.

Perhaps you’re wondering if all foods with sugar impact the brain in these ways. For example, will snacking on fruit have the same impact on the brain as a cookie? According to all four experts, not exactly.

“Cookies and candy are mostly refined sugar and refined flour – they hit the bloodstream quickly, spike blood sugar and don’t bring much nutrition with them.

“Whole fruit, on the other hand, comes in a package with fibre, which slows down how fast sugar is absorbed, vitamins, minerals and antioxidants that help protect brain cells, and water, which helps with fullness and hydration,” Trinh said.

He said this means that when you eat fruit, blood sugar doesn’t rise as quickly and the brain is getting protective nutrients, which doesn’t happen with foods like cookies or candy.

McGrane pointed out that many fruits also contain antioxidants and plant compounds that support brain health, such as anthocyanins in berries, which have been linked to improved cognitive function and reduced inflammation in the brain.

While it’s important to be aware of the connection between sugar and dementia risk, all four experts emphasised that this doesn’t mean you have to cut sugar completely out of your life.

Pascual-Leone shared that experiencing pleasure is important for mood and brain health, and eating foods we love (even if they’re void of nutritional benefits) is part of that. Instead of nixing sugary snacks completely, he recommends eating them in moderation and making it a point to savor the experience when you do have them.

To minimise the spike in blood sugar when you do have a sugary treat, Andrews recommends pairing it with something high in fibre or protein. “Consuming sugar alone is one of the main ways to cause a spike and drop (highs and lows) in your blood sugar, so pairing it with foods that help keep your blood glucose levels even keel will help,” she said.

Don’t wait until you’re hangry to get yourself a snack either. Tingh explained that when blood sugar levels drop (which happens when you haven’t eaten in a while), you’re more likely to reach for the fastest sugar, which is often in the form of something high in added sugars and low in nutritional value. “Having balanced meals and snacks makes it easier to choose wisely,” he said.

Since blood sugar spikes are more dramatic in the latter half of the day and can interfere with sleep, if you are going to have a sugary snack, having it earlier in the day can minimise the impact on your brain.

Want some sweet snack ideas that brain health experts would approve of? Trinh and McGrane are both big dark chocolate fans. “Dark chocolate is rich in cocoa flavanols, which have been shown to support healthy blood flow in the brain and combat inflammation,” McGrane said.

Berries and nuts are another great zero-prep snack option that Trinh recommended. The berries are loaded with brain-supporting antioxidants and the fats and protein in the nuts provide satiety and minimise blood sugar level spikes.

Here’s the biggest takeaway all four experts want people to know: having a diet high in sugar increases the risk of dementia. This doesn’t mean you should avoid sugar completely.

But it does mean you should watch your intake and, when you are enjoying something sugary, it helps to pair it with a food with fibre, protein or fats to blunt the blood sugar spike. When you do have something sugary, enjoy it! After all, that’s what it’s meant for.