Below is a summary of the scientific literature on each ingredient in the Zenergize formula.
Microencapsulated, time-release caffeine lasts longer than regular caffeine and has a smoother onset of action (Gonzalez et al., 2015).* It has a slower absorption rate than regular caffeine and wears off more gradually, rather than leading to a sudden crash (Gonzalez et al., 2015).* While regular caffeine has been found to reach peak plasma levels at 3 hours following ingestion, time-release caffeine has been found to reach peak plasma concentrations at 6 hours following ingestion (Gonzalez et al., 2015). Wells et al. (2014) found that 28 consecutive days of slow-release caffeine ingestion was safe and well tolerated.
Caffeine works by binding to adenosine, a compound that is thought to play a role in regulating the sleep cycle.* Studies have found that caffeine, as well as slow-release caffeine, may support cognitive function and feelings of mental alertness, mood, and arousal (Lagarde et al., 2000, De Valck and Cluydts, 2001, Goldstein et al., 2010, Nehlig, 2010).* Both caffeine and slow-release caffeine may additionally maintain vigilance and choice reaction time (Patat et al., 2000, Lieberman et al., 2002, Mclellan et al., 2005).*
Theacrine is a natural alkaloid which is similar to caffeine (Kuhman et al., 2015). It is found mainly in the leaves of Camellia assamica var. kucha (Kuhman et al., 2015). The difference between theacrine and caffeine is an additional ketone and methyl group. Theacrine is thought to act by antagonizing adenosine receptors, as well as via dopaminergic signaling, similarly to caffeine.* Research suggests theacrine may enhance energy and support calmness (Kuhman et al., 2015).* Unlike caffeine, no changes in in blood pressure, heart rate or jitters were reported from acute dosing of 125mg in one study (Ziegenfuss et al., 2017).* Theacrine does not appear to physically excite the nervous system (Ziegenfuss et al., 2017).* Taylor et al. (2016) found that it is non-habituating.* The combination of caffeine and theacrine may be synergistic, as He et al. (2017) suggest that caffeine may increase the bioavailability of theacrine in humans.* Theacrine appears to have a half life 4 times greater than caffeine, with perceptible effects typically lasting 4 to 8 hours compared to 1 to 2 hours with caffeine (He et al., 2017).*
L-Tyrosine is a non-essential amino acid which is thought to be metabolized to make dopamine.* Dopamine is thought to be associated with motivation, reward and pleasurable feelings (Schultz, 2007, Berke, 2018).* It also appears to play a role in motor coordination of bodily movements, meaning it may potentially also be associated with physical performance (Kawashima et al., 2018).* In a study of 50 Olympic athletes and 100 nonprofessional athletes, Filonzi et al. (2015) suggested that there is a "strong role of dopamine neurotransmitter in determining sport success, highlighting the role of emotional control and psychological management to reach high-level performances." Dopamine is also a precursor for norepinephrine and adrenaline (Joh and Hwang, 1987).* Some evidence suggests that supplementing with tyrosine may support neurotransmitter function and cognitive performance, in cases where the neurotransmitter supply is depleted due to challenging circumstances (Jongkees et al., 2015).* Increasing tyrosine levels may mean that there is more of the amino acid available to be recruited for dopamine synthesis when required (Jongkees et al. 2015).* Tyrosine hydroxylase (TyrH) is thought to limit the rate at which tyrosine can be metabolized to make dopamine (Daubner, Le and Wang, 2010).
L-theanine is a compound reportedly found in green tea, black tea and some mushrooms (Dietz and Dekker, 2017).* Some studies suggest it may support calmness and potentially help to mitigate caffeine induced arousal (Dietz and Dekker, 2017, Hidese et al., 2019).* It has been suggested that it may also support verbal fluency and executive function (Hidese et al., 2019).* L-theanine has a chemical structure said to be very similar to glutamate, a naturally occurring amino acid in the body which may help to transmit nerve impulses (Adhikary and Mandal, 2017).* L-theanine may be metabolized into glutamate (Adhikary and Mandal, 2017).* L-theanine may support dopamine and serotonin production and could perhaps additionally support relaxation through the enhancement of alpha brainwave activity (Nathan et al., 2006, Adhikary and Mandal, 2017).* It has been suggested it might also support GABA levels (Nathan et al., 2006).*
Often called the “king of herbs," panax ginseng is a root said to grow in the mountains of Eastern Asia. It is said to have been traditionally used for promoting energy and supporting resistance to stress (Rokot et al., 2016).* It has been classified as an adaptogen (Rokot et al., 2016).* Panax ginseng may play a role in helping to support the regulation of hormones such as adrenaline, noradrenaline and dopamine, as well as to support calmness during a heightened stress response (Kim et al., 2010, Lee and Rhee, 2017, Tian et al., 2020, Hou et al., 2020).* It may potentially support endurance and stress resistance by mildly stimulating the central nervous system (Barman et al., 2019, Hou et al., 2020).* Ginsenosides and other constituents from ginseng may also potentially support cognition, and help to maintain healthy memory (Kim, 2012, Yeo et al., 2012, Rokot et al., 2016, Lho, Kim and Kwak, 2018, Hou et al., 2020).*
Rhodiola has been classified as an adaptogen, hailing from cold mountainous regions throughout the Northern Hemisphere (Panossian et al., 2007).* It may help to support resistance to stress, possibly by mediating the release of cortisol while simultaneously helping to maintain concentration and alertness (Panossian et al., 2007, Jówko et al., 2018).* Rhodiola may also support physical performance, but evidence of this has been mixed (Walker, 2006, Duncan and Clarke, 2012, Jówko et al., 2018, Ballmann et al., 2019).* It could potentially be beneficial for supporting against stress and fatigue (Spasov et al., 2000, Olsson, 2009, Jówko et al., 2018).* The USSR apparently classified Rhodiola as a viable supplement for their astronauts (Panossian and Wikman, 2010).*
Guarana is said to be a caffeine-rich fruit resembling an eyeball which is indigenous to the Amazon basin.* Native tribes have reportedly used it to support wakefulness and as an aphrodisiac (Konstantinos and Heun, 2019).* A 17th century Jesuit missionary is claimed to have noted that guarana gave members of an Amazonian tribe "so much energy, that when hunting, they could go from one day to the next without feeling hungry" (Betendorf, 1909).* It has been suggested that guarana may work in synergy with caffeine and as such may perhaps be more effective than caffeine alone, but the evidence in support of this claim is lacking (Moustakas et al., 2015, Pomportes et al., 2019, Konstantinos and Heun, 2019).* It also contains tannins and catechins which may potentially help to maintain memory and support cognition (Peixoto et al., 2017, Santana and Macedo, 2018, Konstantinos and Heun, 2019).*
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