Is sugar good for your cognition? Elevated blood glucose levels slow people down on a difficult task.
When you’re feeling sluggish at your desk in the mid-afternoon and you reach for a sugary snack, think again: Anecdotally, sugar intake is linked to both positive and negative outcomes in terms of cognitive performance (think energy drinks vs. hyperactivity) and the scientific literature is equally mixed, with some studies demonstrating an improvement in areas such as memory performance when glucose levels are high, but others showing no effects of glucose.
Now a new study from the Brain and Behaviour group shows that for some tasks, glucose can actually slow you down: and that it depends on how difficult the task is. Chris Hope, Ellen Seiss, Annette Sterr and colleagues carried out two double-blind placebo-controlled studies in which participants performed easy or difficult response time tasks, either after drinking a sugary drink (glucose) or a taste-matched artificial sweetener placebo drink. Participants responded more slowly if blood sugar levels were enhanced by the sugary drink, but only when the task was difficult (involving learning new response rules every few minutes). Thus it seems that glucose doesn’t always enhance performance but under some circumstances can actually slow you down.
Hope C, Seiss E, Dean PJA, Williams KEM and Sterr A (2013) Consumption of glucose drinks slows sensorimotor processing: double-blind placebo-controlled studies with the Eriksen flanker task. Frontiers in Human Neuroscience, 7:651.