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Randomized Controlled Trial
. 2017 Jul 19;9(7):777.
doi: 10.3390/nu9070777.

Reduced Stress and Improved Sleep Quality Caused by Green Tea Are Associated With a Reduced Caffeine Content

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Free PMC article
Randomized Controlled Trial

Reduced Stress and Improved Sleep Quality Caused by Green Tea Are Associated With a Reduced Caffeine Content

Keiko Unno et al. Nutrients. .
Free PMC article

Abstract

Caffeine, one of the main components in green tea, can interfere with sleep and block the effect of theanine. Since theanine, the main amino acid in tea leaves, has significant anti-stress effects in animals and humans, we examined the effects of green tea with lowered caffeine content, i.e., low-caffeine green tea (LCGT), on stress and quality of sleep of middle-aged individuals (n = 20, mean age 51.3 ± 6.7 years) in a double-blind crossover design. Standard green tea (SGT) was used as the control. These teas (≥300 mL/day), which were eluted with room temperature water, were consumed over a period of seven days after a single washout term. The level of salivary α-amylase activity (sAA), a stress marker, was significantly lower in participants that consumed LCGT (64.7 U/mL) than in those that consumed SGT (73.9 U/mL). Sleep quality was higher in participants that consumed a larger quantity of LCGT. In addition, a self-diagnostic check for accumulated fatigue was significantly lower in those participants that consumed LCGT than SGT. These results indicate that LCGT intake can reduce stress in middle-aged individuals and improve their quality of sleep. The reduction in caffeine is suggested to be a valid reason for enhancing the anti-stress effect of green tea.

Keywords: anti-stress effect; caffeine; green tea; middle-aged individuals; salivary α-amylase; sleep.

Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Tea components in SGT and LCGT. One tea bag of SGT or LCGT (3 g of tea in a bag) was steeped in 500 mL of room temperature water (0.5–6 h). Tap water was used in this experiment. Data are expressed as mean ± SD (n = 3). The data of SGT or LCGT was compared with that at 0.5 h, respectively (*, p < 0.05). In addition, LCGT data was compared with SGT data at the same elution time (#, p < 0.05).
Figure 2
Figure 2
Anti-stress effect of LCGT. (a) Mean sAA level of each group. Data are expressed as mean ± SEM (n = 19, *, p < 0.05; one-way ANOVA); (b) Correlation between SGT and LCGT intake; (c) Correlation between the level of sAA before work or after work and SGT or LCGT intake. Data of b and c are expressed as mean ± SEM (n = 5, in each participant).
Figure 3
Figure 3
Level of sAA in each participant. (a) Correlation between sAA before and after work; (b) Correlation of sAA before or after work between during SGT and LCGT intake. Data are expressed as mean ± SEM (n = 5, in each participant).
Figure 4
Figure 4
Effect of green tea intake on sleep parameters or sAA. (a) Early morning awakening. Data are expressed as mean ± SEM (n = 19, *, p = 0.065; one-way ANOVA); (b) Correlation between TST and sAA before work; (c) Correlation between TST and intake volume; (d) Correlation between slow wave sleep (N2+N3) and sAA before work; (e) Correlation between slow wave sleep and intake of SGT or LCGT. Data of b–e are expressed as mean ± SEM (n = 5, in each participant).
Figure 5
Figure 5
Effect of green tea ingestion on subjective stress and fatigue. (a) Subjective stress; (b) physical condition; (c) subjective fatigue; and (d) severity of work. Data are expressed as mean ± SEM (n = 19, *, p < 0.05; one-way ANOVA).

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