According to the CDC, about half of the US population drinks a beverage with added sugar on any given day. Overconsumption of sugar-sweetened beverages (e.g., soft drinks or fruit juice) may lead to health complications such as obesity, type 2 diabetes, or cardiovascular disease, all of which are risk factors for Alzheimer’s disease. A new study published by Miao and colleagues in The Journal of Prevention of Alzheimer’s Disease sought to examine whether consumption of sugar-sweetened beverages may itself be a risk factor for Alzheimer’s disease, irrespective of other comorbidities [1].
The researchers followed a group of individuals who were part of the Framingham Heart Study (FHS) over 20 years. The FHS is an observational cohort study where participants undergo an extensive medical examination, including a questionnaire on diet and beverage consumption, every three to five years. The researchers found that in the 2,664 individuals included in the study, those who consumed one to seven servings of sugar-sweetened beverages per week were 1.91 times more likely to develop Alzheimer’s disease than those who consumed no sugar-sweetened beverages. In addition, those who consumed more than seven servings of sugar-sweetened beverages per week were 2.55 times more likely to develop Alzheimer’s disease. This was after controlling for other potential risk factors such as hypertension, smoking, diabetes, and body mass index. Similar results were reported for stroke, with the consumption of sugar-sweetened beverages increasing the risk of stroke.
Intriguingly, these results are in contrast from a previous study by Pase and colleagues who reported that the consumption of sugar-sweetened beverages did not increase the risk of Alzheimer’s or stroke in the FHS population [2]. Several explanations could account for these discrepant results. First, each study used a different design. Pase and colleagues studied individuals in their early 60s and followed them for 10 years, while Miao and colleagues studied individuals in their mid-50s and followed them for 20 years. Possibly, the association between consumption of sugar-sweetened beverages and the risk of Alzheimer’s does not emerge until after 20 years.
In addition, the two studies defined the number of beverages consumed per week in different ways. For instance, one study compared individuals who drank less than one sugar-sweetened beverage per day to those who drank more than two per day while the other compared individuals who drank no sugar-sweetened beverages per week to those who drank more than seven. In addition, both studies used different statistical adjustments to measure the risk of Alzheimer’s disease.
These discordant observations exhibit the inherent difficulties in defining risk factors for Alzheimer’s disease from observational studies. Observational studies can only show associations between risk factors and disease and not the actual causes of a disease. In addition, certain behaviors may be associated with other risk factors. For instance, in the study by Miao and colleagues, those who consumed more than seven sugar-sweetened beverages per week were also more likely to consume more calories, saturated fat, and less dietary fiber, which the researchers did not control for.
How might consumption of sugar-sweetened beverages increase the risk for Alzheimer’s? Overconsumption of sugar-sweetened beverages may increase the risk of type 2 diabetes, itself a risk factor for Alzheimer’s [3]. It could also make your body resistant to insulin, a hormone that regulates blood levels of sugar. This condition, referred to as insulin resistance, is also a common feature in Alzheimer’s disease [4]. Finally, in animal models, a high sugar diet also reduced the level of brain-derived neurotrophic factor (BDNF), which may decrease the number of connections between brain cells [1; 5].
Sugar-sweetened beverages increase the risk of diseases associated with dementia, even if there is mixed evidence directly relating them to Alzheimer’s disease. Diabetes, cardiovascular disease, and obesity, all complications associated with over consumption of sugar-sweetened beverages, increase the risk of future dementia. So, remember, keeping in line with our Seven Steps to Brain Health, a healthy diet is not just the food you eat but also what you drink.
Nick McKeehan is a member of the ADDF's Aging and Alzheimer's Prevention program. He evaluates the scientific evidence for and against therapies to promote brain health and/or prevent Alzheimer's disease at our website CognitiveVitality.org and contributes regularly to the site's blog. Mr. McKeehan previously served as Chief Intern at Mid Atlantic Bio Angels (MABA) and was a research technician at Albert Einstein College of Medicine investigating repair capabilities of the brain. Mr. McKeehan received a bachelor of science degree in biology from Purdue University, where he was awarded a Howard Hughes Scholarship. He also writes about the biotechnology industry for 1st Pitch Life Science.
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