People are living longer than ever, but many are not spending those extra years in great health, and dementia remains one of the biggest threats to quality of life. Researchers estimate that roughly 45 percent of dementia cases may be preventable through changes in diet and everyday habits. One surprisingly common routine that may work against brain health is reaching for sugary snacks in the afternoon. It can feel harmless, yet experts say timing and repeated blood sugar spikes may matter more than most of us realize.
A growing body of research links high sugar diets with a higher risk of dementia, and specialists are increasingly calling out the afternoon sweet tooth. Registered dietitian Julie Andrews explains that sugary foods can trigger a rapid jump in blood glucose, which then sets off a cascade of effects throughout the body. “Studies show that large variations in blood glucose over a long period of time, both high and low, can increase dementia risk because they 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 affect anyone, not only those with diabetes,” Andrews said. The concern is not a single cookie on a stressful day, but the steady pattern of big swings that repeat for months and years.
Dr. Alvaro Pascual-Leone, a professor of neurology at Harvard Medical School, connects those swings to how the brain uses energy. He notes that chronically unstable blood sugar can contribute to brain insulin resistance, meaning brain cells cannot use glucose efficiently. That scenario is sometimes informally described as type 3 diabetes, and it has been linked to memory loss and dementia. Dr. Dung Trinh, chief medical officer of the Healthy Brain Clinic, also highlights the damage that can follow when blood sugar is frequently unstable. He points to blood vessel injury, oxidative stress, and disruption in how brain cells produce and use energy.
The issue is not only about metabolism, because sugar can also shape the brain’s reward system. Dietitian Kelli McGrane notes that sweet foods tend to pull us back for more by reinforcing cravings. “One reason sugar is so appealing is that it triggers dopamine release in the brain’s reward pathway. While occasional or moderate intake is usually not concerning, consistently high sugar intake can overstimulate this system. Over time, that can negatively affect learning, memory, mood regulation, and even motivation,” she explained. In other words, an afternoon candy habit can become self sustaining, even when it does not match what your body actually needs.
Experts say afternoon sugar can be especially troublesome because our tolerance to glucose tends to be lower later in the day. Dr. Pascual-Leone explains that blood sugar spikes in the second half of the day can be more pronounced, which is a problem if those spikes happen regularly. There is also a sleep connection that can magnify the impact, since late day sweets can interfere with falling asleep or staying asleep. Specialists widely agree that good sleep is central to dementia prevention. Dr. Pascual-Leone points out that sleep supports the brain’s cleanup processes, helping clear neurotoxic proteins such as beta amyloid and tau.
When those proteins are not cleared effectively, they can accumulate and disrupt communication between neurons, which has been tied to dementia. That is why an afternoon habit that both spikes blood sugar and chips away at sleep can be a double hit. The pattern can look small on any single day, but the brain responds to what happens consistently. If you notice that you crave sweets around the same time each afternoon, it may be a useful signal to adjust your routine. Sometimes the craving is actually hunger, dehydration, stress, or simply fatigue that your body is trying to fix quickly.
A common question is whether fruit counts as “sugar” in the same risky way, and the experts draw a clear line between whole fruit and processed sweets. Dr. Trinh stresses that cookies and candy behave differently in the body than fruit does. “Cookies and candy are mostly refined sugar and refined flour, they enter the bloodstream quickly, sharply raise blood sugar, and do not provide many nutrients. Whole fruit, on the other hand, comes packaged with fiber that slows the rate of sugar absorption, plus vitamins, minerals, and antioxidants that help protect brain cells,” Trinh said. McGrane also notes that many fruits, including berries, contain plant compounds such as anthocyanins that have been associated with better cognitive function and lower brain inflammation.
The goal is not to erase sugar from your life, but to handle it with awareness and moderation. Dr. Pascual-Leone emphasizes that pleasure matters for mood and brain health, so deprivation is not the point. Andrews suggests softening the glucose spike by pairing a sweet treat with fiber or protein, which can slow absorption and reduce extremes. It also helps not to wait until you are intensely hungry, because that is when ultra sweet, ultra processed options become hardest to resist. If you do choose a sugary snack, experts suggest having it earlier in the day to reduce its impact on both the brain and sleep.
For people looking for smarter ways to satisfy a sweet craving, Dr. Trinh and McGrane suggest options that bring benefits along with flavor. Dark chocolate is one example, since it contains flavanols that support blood flow in the brain. A snack of berries with a handful of nuts can also provide sweetness plus fiber, healthy fats, and micronutrients. The broader message is simple, a high sugar diet can raise dementia risk, but mindful choices can reduce that risk without turning food into an enemy. Small swaps repeated daily are often more powerful than dramatic overhauls that do not last.
Dementia is an umbrella term for conditions that affect memory, thinking, and daily functioning, and Alzheimer’s disease is the most common type. Vascular changes also play a major role in many cases, which is why blood vessel health and inflammation keep showing up in prevention conversations. The brain uses a large share of the body’s energy, so steady access to fuel matters, and that is part of why researchers focus on glucose regulation and insulin signaling. Sleep is another pillar because it supports memory consolidation and helps the brain clear metabolic waste, which is why afternoon sugar that disrupts rest can have outsized consequences over time.
Have you noticed an afternoon sugar routine in your own day, and what changes have helped you keep cravings in check while still enjoying food, share your thoughts in the comments.
