Fructose-Induced Cognitive Dysfunction Is Associated with Increased Oxidative Stress in the Rat Brains

Evidence is emerging that obesity and type 2 diabetes are often associated with cognitive impairment. Fructose, or fruit sugar, is a simple ketonic monosaccharide found in many plants. Recent studies have reported a role of excessive fructose intake in the onset of type 2 diabetes in rodents and humans.

To determine if fructose intake might affect memory function independently of diabetes development, the authors in this paper investigated the effects of monosaccharides on memory in prediabetic state. They examined whether 2.5% apple juice solution could influence cognitive function in salt-sensitive Dahl rats using passive avoidance methods. Furthermore, the authors examined the role of monosaccharides intake in cognitive function and oxidative stress in the brain.

Four-week consumption of either apple juice or 2.5% fructose did not affect the blood glucose concentrations; however, apple juice, but not fructose, significantly decreased cognitive function compared with that of control rats given water. Second, Wistar rats aged 4 weeks were assigned to four groups given water, or 1.25% glucose, or fructose, or galactose solutions for 11 weeks. The fructose group had only slightly higher blood glucose concentrations than the control group. However, memory function engraved at age of 7 weeks and evaluated for 8 weeks in a passive avoidance test, was significantly decreased in the fructose and galactose groups compared with those in the glucose group. Oxidative stress in the brain, assessed by the tissue malondialdehyde (MDA) content, was significantly increased in the fructose group compared with that in the control group, and the decrease in cognitive function significantly correlated with the MDA content.

In conclusion, these findings demonstrate that long-term fructose intake is associated with impaired memory function and increased oxidative stress in the rat brain. Memory was also impaired in rats given apple juice rich in fructose, without overt hyperglycemia. These results suggest that fructose-intake-associated memory impairment is not related to insulin resistance but, rather, is caused by fructose loading per se. Fructose intake may need to be reduced to the minimum level required for healthy living.

Article by En Yabe, et al, from Japan.

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