There’s now one more reason to curb your child’s or teenager’s sweet tooth as new research shows high sugar consumption is linked to impaired learning and memory later on in life.
Children are the greatest consumers of added sugar and while high sugar intake has long been associated with negative health effects such as obesity and heart disease, little has been known about the link between sugar and brain development.
To find out more, a researcher from the University of Georgia collaborated with a research group at the University of Southern California and using a rodent model, found that high sugar consumption in adolescent rats led to poor learning and memory performance. The researchers found that the cognitive impairments were associated with changes in the gut microbiota induced by high sugar levels. They specifically found that consuming excess sugar early on in life leads to an increase in levels of Parabacteroides bacteria.
The research revealed that daily consumption of sugar-sweetened beverages during adolescence impairs performance on learning and memory tasks during adulthood by affecting the developing hippocampus. The hippocampus is the region of the brain that regulates learning and memory, in addition to things like motivation and emotion.
The study, published in the journal Translational Psychiatry, sheds light on yet another negative outcome of excess sugar consumption with respect to a concerning link between excess sugar and brain development.
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Given that the hippocampus regulates a variety of cognitive functions, and that it is still developing into late adolescence, the researchers wanted to learn about its susceptibility to a high-sugar diet. Moreover, there has been increasing evidence that the gut microbiome is implicated in neurocognitive development. Given this, the researchers were able to propose a new mechanistic link between hippocampal function and changes in the gut microbiota caused by high sugar intake.
Sugar and Brain Development
For the study, juvenile rats were given their normal feed and an 11 percent sugar solution, which is comparable to commercially available sugar-sweetened beverages. The researchers assessed memory function and anxiety-like behavior during adulthood, and also conducted gut bacterial and brain transcriptome analyses.
The researchers then had the rats perform a hippocampus-dependent memory task designed to measure episodic contextual memory, which involves remembering the context where they had seen a familiar object before. Results of this experiment revealed that rats that were given the sweetened solution early in development had impaired ability to discriminate whether an object was novel to a specific context, whereas rats that did not consume the sugar solution were able to do so.
A second memory task was used to evaluate basic recognition memory, a hippocampal-independent memory function that involves an animal’s ability to recognize something they had seen in the past. The researchers found that sugar had no effect on the rats’ recognition memory in this task.
“Early life sugar consumption seems to selectively impair their hippocampal learning and memory,” said Emily Noble, assistant professor in the UGA College of Family and Consumer Sciences and first author on the paper.
The chronic consumption of sugar early in life impaired adult hippocampal-dependent memory function without affecting body weight or anxiety-like behavior.
Sugar-Induced Changes in the Gut Microbiome
To explore potential mechanisms underlying the observations, the researchers conducted taxa-specific microbial enrichment experiments to examine the functional relationship between sugar-induced microbiome changes and neurocognitive and brain transcriptome outcomes. Through these analyses, the researchers found that high sugar intake led to elevated levels of two species in the genus Parabacteroides (P. distasonis and P. johnsonii) in the gut microbiome that had a negative correlation with hippocampal function.
To assess the microbial impact on memory and learning, the researchers experimentally elevated levels of Parabacteroides in the microbiome of rats that had never consumed sugar. These animals showed impairments in both hippocampal dependent and hippocampal-independent memory tasks, and thus the bacteria alone could induce some of the cognitive deficits on their own.
“Early life sugar increased Parabacteroides levels, and the higher the levels of Parabacteroides, the worse the animals did in the task,” said Noble. “We found that the bacteria alone was sufficient to impair memory in the same way as sugar, but it also impaired other types of memory functions as well.”
Noble said future research is needed to better identify specific pathways by which this gut-brain signaling operates. “Identifying how the bacteria in the gut are impacting brain development will tell us about what sort of internal environment the brain needs in order to grow in a healthy way.”
Currently, the Dietary Guidelines for Americans, a joint publication of the US Departments of Agriculture and of Health and Human Services, recommends limiting added sugars to less than ten percent of calories per day.
Data from the Centers for Disease Control and Prevention (CDC) shows that Americans between the ages of nine and 18 exceed this recommendation with the majority of the sugar-based calories coming from sugar-sweetened beverages.
The new research raises further red flags on excess sugar consumption among children and teens, a concerning trend that has detrimental implications for both physical and cognitive health later in adulthood.
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