Does creatine supplementation improve cognitive function in sleep restricted healthy men and women?

Study overview A double-blinded, randomised, placebo-controlled, cross-over design trial was conducted in men and women to compare the effect of creatine-monohydrate loading and a placebo (PLA) on cognitive performance, mood, sleepiness, subjective workload and cerebral neurovascular coupling following sleep restriction (3 hours TIB). Experimental procedures Prior to the study, participants were familiarised with the cognitive test battery by performing it 5 times within the 7 days prior to commencing the study to minimise practice effects. In the morning following two consecutive nights of at least 8 hours TIB (approximately 2200-2230 to 0600-0630), participants presented to the laboratory between 0730-0930 in a fasted and rested state to complete the testing protocol (day 1; baseline). Immediately afterwards, participants commenced their dietary supplement allocation (i.e. creatine-monohydrate or PLA) for 7 days, as per prior randomisation (www.randomizer.org). Sleep was monitored daily via actigraphy. Participants were requested to maintain habitual bed and rise times (approximately 8 hours TIB) between days 1 to 6. On day 7, participants were requested to restrict sleep to 3 hours TIB (0330 to 0630). During the study, participants were requested to abstain from over the counter medications, alcohol, napping, and remain hydrated. Caffeine intake was limited to <100 mg/day ingested before 1200 and prohibited for the 24 hours prior to testing. Ingestion of meat and fish was prohibited during the 24 hours prior to testing to minimise variability arising from dietary intake of creatine. Physical activity was requested to be maintained at moderate levels. All other lifestyle choices were allowed to vary naturally during the study period. Following sleep restriction (day 8; post-intervention), participants presented to the laboratory between 0730-0930 in a fasted and rested state to repeat the testing protocol. Following completion, participants were asked to state what supplement protocol they were randomised to. The washout period between treatments was at least 5 weeks as this appears to reduce tissue creatine concentrations to approximately baseline (pre-supplement) levels. After the washout period, participants repeated the experimental protocol with the alternative supplement treatment. Dietary supplementation Participants ingested 20 g/day creatine monohydrate or tapioca. Supplements were mixed with 3 g of lime-flavoured drink powder to ensure taste and colour matching. Supplements were made in a research grade kitchen and provided in powdered form to be mixed with water for consumption. Participants ingested 4 doses daily, at equally spaced intervals, on days 1 to 7. A creatine-monohydrate loading strategy of 20 g/day for 7 days was chosen as this has been shown to augment creatine stores within the brain of men and women. Participants were requested to send a text message to the researchers to confirm ingestion at the end of each day. Testing protocol Participants rested in a quiet room. The cognitive test battery took ~20 min to complete and was divided into: 1) 10-minute psychomotor vigilance task (PVT) and measurement of cerebral tissue oxygenation; and 2) working memory, logical relations and executive function using the computerised Automated Neuropsychological Assessment Metrics (ANAM®). Immediately afterwards, mood, sleepiness and subjective workload were measured using the ANAM® mood scale, Stanford Sleepiness Scale and NASA Task Load Index (NASA-TLX) that excluded the weighting component. PVT-192 task Vigilant attention was measured using the 10-minute version of the PVT. Participants responded to the presentation of a visual stimulus as quickly as possible by pressing a button with the thumb of their dominant hand. Running memory continuous performance test Working memory and vigilant attention was measured using a 3-minute running memory continuous performance test (RMCPT), which is a continuous reaction time (RT) test using a standard “two-back” paradigm. Participants were required to recall the numerical digit (0–9) that appeared on the screen two prior to the current digit and respond as to whether the digit is the same or different. Logical relations Abstract reasoning was measured using a ~2 minute logical relations test. Participants were required to evaluate the truth of a statement (e.g. "# comes before &") describing the order of two symbols displayed on the display (e.g. "& #") and indicate whether the statement is true or false by a left or right mouse click, respectively. Stroop Processing speed, selective attention, interference, and executive functioning were measured using a ~3 minute Stroop test. There were three blocks of trials for this test: colour-naming, word-reading, and colour-word interference conditions. Mood The ANAM mood scale, measuring fatigue and vigour, consisted of six adjectives displayed on a 7-point Likert scale anchored with 0 (not at all) to 6 (very much). Fatigue adjectives included lazy, inactive, tired, weary, sluggish, and drowsy, whilst vigour adjectives included energetic, lively, alert, spirited, active, and vigorous. Cerebral oxygenation measurement Multichannel fNIRS (Octamon, Artinis Medical, The Netherlands) was used to quantify changes in cerebral haemoglobin oxygenation. Sleep/wake monitoring Participants wore a wrist actigraph (Micro Motionlogger Watch; Ambulatory Monitoring Inc., Ardsley, New York, USA) on their non-dominant wrist at all times during the study, except when showering and swimming.