The ability to store memories may be linked to a person's blood sugar level, according to researchers at the University of Virginia.
Psychologist Paul Gold and his co-workers found in experiments that the performance of elderly subjects on memory tests improved markedly after they had been given a glass of sweet lemonade.
Gold tested the group first with lemonade containing 2 1/2 to 5 teaspoons of sugar and then again with lemonade sweetened with saccharine. After the sugar drink, the volunteers performed 30 percent to 40 percent better on "declarative memory tests" -- tests for things and events as opposed to procedures like riding a bicycle -- than they did after drinking the saccharine drink.
Declarative memory is the type most often impaired in the elderly.
Glucose appears to enhance memory storage for at least 24 hours, Gold said. How it works and why, however, remain mysteries. Since the late 1980s researchers have known that glucose, the form of sugar used in the experiments, and another substance -- epinephrine -- somehow help signal the brain that, as Gold says, "this is something to remember." But the precise brain mechanism that the sugar operates on is not known.
Nor is it clear whether glucose has the same effect on people with normal memory. Similar experiments on animals -- both normal and with impaired memories -- showed the sugar effect in both. But experiments on children failed to show any sugar effect.