In the news: Sugary Diets May Raise Alzheimer’s Risk

Alzheimer’s: Background and Research

Researchers do not fully understand which changes in the aging brain may cause Alzheimer’s disease. Is it due to an accumulation of beta-amyloid protein? Is the culprit a buildup of tau protein inside neurons? Or, as emerging evidence suggests, is Alzheimer’s caused by a complex interplay among these two proteins and other risk factors such as impaired brain glucose metabolism and insulin resistance, and chronic inflammation?

Alzheimer’s develops over many years and beta amyloid starts accumulating in the brain decades before it impacts cognition. The earlier stage of development is referred to as ‘preclinical Alzheimer’s’, and researchers study biomarkers like brain beta-amyloid levels in individuals to learn more about how diet and lifestyle may prevent or delay this disease.

One area being explored is the relationship between glucose metabolism and Alzheimer’s(1). We know that the amount and type of carbohydrates we eat influences glucose metabolism. High glycemic index foods (sugar and refined / processed carbs) cause blood sugar to spike and insulin to be released.

Too Much Sugar May Up Alzheimer’s Risk?

Since existing evidence suggests that glucose metabolism may be related to cerebral amyloid, researchers at the University of Kansas Alzheimer’s Disease Center explored the relationship between dietary glycemic measures and cerebral amyloid levels in older individuals with normal cognitive abilities(2).

Using brain scans to determine the burden of amyloid in various regions of the brain, they compared a pattern of habitually eating a high glycemic diet with changes in brain amyloid levels over one year.

Among all the participants, those with the greatest habitual high-glycemic diet scores, higher sugar and total carbohydrate intakes had more amyloid accumulation in an area of the brain (precuneus) associated with body awareness.

The link between these dietary measures and precuneal amyloid was even stronger for participants who already had elevated amyloid at the study’s start. For those individuals, a high glycemic diet was also associated with more amyloid accumulation in the brain area (lateral temporal lobe) that functions in comprehension, hearing, visual processing, and facial recognition, and in an area (posterior cingulate gyrus) thought to be important in cognition.

Interestingly, in a previous study(3) by the same research group, only sugar intake was associated with measures of cognitive performance: higher sugar consumption was linked to poorer mental performance.

Sugary Drinks Tied to Alzheimer’s Risk

Other investigators are looking into the association between sugary beverages and Alzheimer’s. In an analysis(4) of 2600+ Framingham Study participants that were followed for 20 years, researchers found that those who drank 1-7 servings of sugar-sweetened beverages weekly were 1.9 times more likely to develop Alzheimer’s than those who consumed none. Those drinking more than 7 servings of these beverages/week were 2.5 times more likely to develop the disease.

It’s going to require more research before we know whether eating a healthier glycemic diet may reduce the risk of Alzheimer’s. In the meantime, avoiding a high-glycemic index diet makes good sense since it has also been linked to a higher risk of cardiovascular disease, age-related macular degeneration, and cataract formation.

References

1. Alves SS, et al. Review: Insulin resistance as a common link between current Alzheimer's Disease hypotheses. J Alzheimer’s Dis. 82:71-105, 2021.
2. Taylor MK, et al. High glycemic diet Is related to brain amyloid accumulation over one year in preclinical Alzheimer's Disease. Front Nutr. 8:741534, 2021.
3. Taylor MK, et al. A high-glycemic diet is associated with cerebral amyloid burden in cognitively normal older adults. Am J Clin Nutr. 106:1463–70, 2017.
4. Miao H, et al. Sugar in beverages and risk of incident dementia, Alzheimer’s disease and stroke: A prospective cohort study. J Prev Alz Dis. 2:188-93, 2020