Oxidative stress, reflecting the accumulation of oxygen- containing free radicals, increases with aging and may play a key role in age-related functional deficits of the brain and other organs, such as the heart. Blueberries are one of the foods with the greatest ability to neutralize oxygen-containing free radicals. In rodent models of brain aging, dietary blueberry supplementation impeded the development of impairments in neurochemistry, synaptic transmission, and behavior. Aging human beings tend to be impaired in visual object recognition memory.

A non-spatial object recognition memory task tests a rat's memory for previously explored objects. The task, which requires no deprivation or punishment, is based on rats' innate tendency to preferentially explore novel versus familiar objects. Task performance depends on intact hippocampal function.

Two studies found that aging impaired memory for visual object recognition, although another study detected no consistent age-related trend.

Another study found that middle-aged (19-mo), but not young, Fischer-344 rats had highly impaired memory for this visual object recognition task in a manner dependent on retention interval. The aging rats were not impaired when there was only a 30-s delay between object familiarization and testing. However, with a 1-h delay, aging rats performed no better than chance. In contrast, aging rats fed a diet supplemented with lyophilized blueberries (2% by weight) for 4 mo (age 15-19 mo) performed as well as young rats.

The active form (p65) of nuclear factor-kB, a sensitive indicator of oxidative stress and inflammation, was elevated in brains of aging rats compared with young rats. The 4-mo blueberry-supplemented diet largely prevented the elevation of nuclear factor-kB levels in aging rats. Nuclear factor-kB levels, averaged across all evaluated brain regions, correlated negatively and significantly with object memory performance. Also, levels in the hippocampus alone and the cerebellum alone each correlated negatively and significantly with performance.

Taken together, these results are consistent with the hypothesis that blueberry supplementation improved object memory through decreasing oxidative stress.

Fig. 1. Change in object recognition memory scores from 19 to 20 month in Fischer- 344 rats maintained during that 1-mo interval on a BB diet or an isocaloric control diet. BB, 2% blueberry-enriched.

The present study (Fig. 1) is encouraging in terms of potential human application:

1. The present results suggest that even a relatively brief blueberry diet might produce measurable benefits.
2. The benefits of several months of the diet might be maintained for a considerable period after the diet is interrupted.
3. Blueberry supplementation might possibly reverse some degree of memory impairment that has already developed.

This raises the possibility that this sort of nutritional intervention might still be beneficial even after certain memory deficiencies have become evident.