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| Study | Cognitive tests and psychological rating scales | Chewing objects | Summary of results (compared with nonchewing condition unless stated) | Attributes of effects on attention |
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| Wilkinson et al. (2002) [10] | 15 tests on memory and attention | Sugar-free spearmint gum | Improvements of scores on episode and working memory and simple reaction time. Elevation of heart rate. No significant differences in attention. | Not significant |
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| Tucha et al. (2004) [11] | 12 tests on memory and attention | Sugar-free spearmint gum and sugar-free tasteless gum | Shortening of reaction time on sustained attention, prolongation of reaction time on alertness, and increase of number of errors on flexibility. No significant differences in memory and pulse rate. | Positive or negative depending on task |
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| Stephens and Tunney (2004) [37] | 8 tests on memory and attention | Sugar-free mint flavored gum | Improvements of scores on episode and working memory, attention, and processing speed. No significant differences in executive function. | Positive |
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| Kohler et al. (2006) [36] | Psychomotor vigilance, tracking, and grammatical reasoning and alertness | Parafilm (sugar-free, tasteless) | Not significant or detrition of performance of speed and accuracy on simple and complex cognitive tasks except for a simple motor tracking task early during the period of sleep deprivation. No significant differences in alertness, heart rate, and root mean square of successive differences in R-R intervals. | Positive or negative depending on task and time |
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| Sakamoto et al. (2009) [15] | Reaction time | Odorless and tasteless gum base | Shortening of reaction time and the peak latencies of event-related potentials (P300 and N100) in second and third session after chewing. | Positive |
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| Smith (2009) [16] | Mood, alertness, intelligence test, and short term and working memory | Volunteer’s preferred gum | Improvement of intelligence test. No significant difference in memory. Increased alertness at the end of the test session. | Positive |
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Scholey et al. (2009) [21] | 4 tests including memory, attention, and mood | Volunteer’s preferred gum | Overall better performance on the cognitive tasks. Increase of alertness and reduction of stress and salivary cortisol. | Positive |
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| Smith (2009) [18] | 5 tests on alertness and mood | Caffeinated gum or placebo gum | More positive mood after chewing and at the end of the study regardless of caffeine. Higher alertness after chewing. No significant difference in alertness without caffeine. | Not significant |
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| Sakamoto et al. (2009) [14] | Reaction time | Odorless and tasteless gum base | Shortened reaction time at third trials after chewing. Increased contingent negative variation (CNV) at second and third trials after chewing. No significant differences in movement-related control potentials. | Positive |
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| Tänzer et al. (2009) [30] | 16-minute concentration test | Sugar-free fruit gum | Improvement of concentration performance with time in 8-9-year-olds. | Positive |
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| Smith (2010) [17] | 10 tests on memory, attention, and mood | Spearmint or fruit gum | Improvement of alertness and selective and sustained attention. Shortened reaction time; this effect became bigger as the task became more difficult. Increase of heart rate and saliva cortisol. | Positive |
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| Tucha et al. (2010) [42] | Vigilance and sustained attention | Sugar-free spearmint gum | Deterioration of vigilance performance in both healthy children and children with ADHD (mean age 10.8 years). No significant difference in sustained attention. | Negative |
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| Tucha and Simpson (2011) [29] | Sustained attention | Sugar-free spearmint gum | Detriment on sustained attention in earlier stages of 30-minute task and benefit on sustained attention at later stages. | Negative early to positive later within 30-min period |
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| Johnson et al. (2011) [25] | 4 tasks including memory and attention, mood, and alertness | Regular chewing gum | Increase of self-rated alertness and stress. No significant differences in task performance and saliva cortisol. | Positive |
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| Onyper et al. (2011) [41] | 5 tasks including memory and attention | Spearmint or doublemint gum with or without sugar | Improvements of performance of several tasks in chewing for 5 minutes prior to testing. No significant differences in chewing throughout testing. | Positive in chewing prior to testing |
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| Sketchley-Kaye et al. (2011) [26] | Acute stress task, mood, anxiety, and alertness | Regular chewing gum | Attenuation of state anxiety and increase of alertness under condition of acute social stress task. No significant differences in contentedness or calmness. | Positive |
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| Allen and Smith (2012) [31] | 4 tasks on attention and mood | Volunteer’s preferred gum | Increased alertness, mood, and performance of attention test and shortened reaction time. Initial extended vigilance reaction times were shortened after trials. | Positive, but some tests showed negative effects initially |
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| Allen and Smith (2012) [38] | 4 tasks on attention and mood | Volunteer’s preferred gum | Increased reported alertness for positive and neutral demand characteristics. Improved selective attention. Reduced performances of two attention tasks only at specific time of trials. Better response organization on categoric search task when demand characteristics and pretest attitudes to gum were both negative. | Positive, but some tests showed negative effects at specific time of trials |
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| Hirano et al. (2013) [12] | Alerting and executive control | Odorless and tasteless gum base | Shortened reaction time. No significant differences in alerting and conflict effects. Higher activations in the anterior cingulate cortex and left frontal gyrus for the executive network and motor-related regions for both attentional networks | Positive |
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| Johnson et al. (2013) [28] | Sustained attention, alertness, and mood | Cool Breeze gum | Improved attentional task performance. Higher alertness and mood. Shortened response times. No time-on-task effect. | Positive |
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| Morgan et al. (2014) [32] | Short-term memory, vigilance, and mood | Sugar-free spearmint gum | Attenuated time-dependent decrement on both performance and subjective alertness. Shorter correct reaction time in the latter stage of the task. | Positive, especially in the latter stage of the task |
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| Allen et al. (2014) [35] | Vigilance and mood | Gum base | Shortened reaction time and increased rate of hits. Heightened heart rate during chewing. Increased EEG beta power at F7 and T3 immediately after chewing. | Positive |
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