Fatigue in healthy people is an important biological alarm system that acts as a cue to rest. However, long-lasting or extensive fatigue can have a negative effect on quality of life.
Oxidative stress is involved in the mechanism of exercise-induced fatigue [1
] and mental stress [2
] in healthy humans, as well as the pathophysiology of prolonged fatigue (chronic fatigue syndrome) [3
]. One biological marker of oxidative stress is phosphatidylcholine hydroperoxide (PCOOH), which is the major phospholipid hydroperoxide in plasma [6
]. Because phospholipids, including phosphatidylcholine, are a major component of cell membranes, extensive lipid peroxidation can lead to loss of fluidity, falls in membrane potential and eventual rupture, leading to release of cell and organelle contents [7
Astaxanthin is a red oceanic carotenoid that is found in shellfish, algae and fish. Its strong antioxidative activity has been reported by several groups [8
]. In particular, its singlet oxygen quenching ability was reported to be approximately 1000 times more effective than coenzyme Q10 [8
]. Various biological activities have been reported for astaxanthin, such as anti-inflammatory [10
], skin moisture-improving [11
], immune-stimulatory [12
] and neuroprotective activities [13
]. For example, astaxanthin attenuates amyloid β induced erythrocyte damage in vitro and in vivo [14
]. Dietary intake of astaxanthin has also been shown to improve erythrocyte antioxidant status and decrease phospholipid peroxide levels in humans [6
Sesame is an oleaginous seed which has traditionally been considered to be a health food in Japan and other Asian countries. Sesamin is one of the lignans abundantly present in sesame seed. Sesame seed extracts display antioxidant activity in the β-carotene/linoleic acid system, which evaluates inhibition of the formation of free radicals generated during the peroxidation of linoleic acid [15
]. Their antioxidative activities can be attributed to the presence of antioxidant lignans such as sesamin [16
Several studies have tested the effects of astaxanthin or sesame lignan separately on fatigue. Hongo et al., reported that astaxanthin reduced daily fatigue stemming from mental and physical causes [17
]. Takemoto et al., evaluated the effects of supplements including sesame lignans and vitamin E on subjective outcomes such as fatigue, sleep and physical appearance [18
]. However, the combination of these two components has never been studied for anti-fatigue activity. The objective of this study is to investigate the effect of a mixed supplement containing astaxanthin and sesamin (AS) on daily fatigue. We evaluated subjective fatigue using markers of daily fatigue (visual analog scale (VAS) for fatigue and the Chalder fatigue questionnaire (CFQ)).
The flow diagram in Figure 2
provides an overview of all included and excluded participants. Participants who could endure the fatigue-inducing tasks were included after second-order screening. A total of 24 participants were qualified for allocation after two screenings, and 23 participants completed the study. One participant discontinued after the washout period due to abnormal blood test values which were unrelated to the intake of the test supplement according to the study doctor. During the physical task, workload was reduced in one participant from 45 watt to 34 watt due to the study doctor’s decision based on the increase in heart rate. The variation of heart rate during the physical task was from 70 ± 9 for the initial time point to 82 ± 10 at the end of 4 h physical task. No statistically significant differences in baseline characteristics were observed between the two groups in terms of age, sex, body mass index, fatigue score (CFQ and VAS) at first-order screening (Table 1
) and workload during the physical task at second-order screening. For efficacy evaluation, 22 participants were included in the per-protocol efficacy analysis; one participant who dropped out of the study and one participant who was considered to meet exclusion criterion 2 (severe fatigue) due to shingles were excluded from efficacy analysis. For the web questionnaire, assessments completed on the Japanese national holiday (23 November 2016) and during Silver Week, a string of Japanese national holidays (21 September 2016), were excluded from statistical analysis. Ingestion rates of the AS and placebo periods were 99.6 ± 1.5% and 98.6 ± 3.5%, respectively. There was no significant difference between the two test conditions in ingestion rate.
3.2. Subjective Fatigue Score on Mental and Physical Task Days
The order effect and the period effect in the crossover design were determined for the VAS at all test days (initial test day, mental task day and physical task day) for both all subjects and eligible subjects. Neither a significant order effect nor period effect were found. Therefore, this study was considered adequate as a crossover study.
On the mental task day, the 2-way repeated-measures ANOVA revealed no interaction, and showed significant time factor, indicating that the subjective fatigue changed along with task (Figure 3
a). There was no significant difference between AS and placebo, when task period and recovery period were combinedly analyzed. In the difference from score at the end of the mental task, there was a significant difference between AS and placebo (Figure 3
b). VAS scores during the physical task were assessed on the day after mental task. The difference between initial VAS score on the physical task day and the mental task day was statistically significant between AS and placebo supplementations; this was considered to be a carry-over effect. Therefore, VAS scores on the physical task day were considered not valid.
VAS scores were also assessed before and after four weeks of supplementation. The scores before and after four weeks of supplementation were 51.4 ± 16.4 and 53.6 ± 18.8, respectively, for AS supplementation and 49.9 ± 19.1 and 50.2 ± 17.6, respectively, for placebo supplementation. Significant differences between AS and placebo supplementation were not observed.
3.3. Fatigue Questionnaires Using CFQ
CFQ scores were assessed every Wednesday via web questionnaires. A 2-way repeated-measures ANOVA revealed that the interaction and the effect of supplementation was not significant. There was a significant difference in time (p = 0.02). About the difference from the initial score, the interaction and the effect of supplementation was not significant. There was a significant difference in time (p < 0.01).
3.4. Secondary Outcomes
For autonomic nervous function, spectral analysis of a–a interval of accelerated plethysmography was performed both before and after four weeks of supplementation and during and after both the mental and physical tasks. LF/HF values before supplementation and after supplementation and the difference between these were 1.867 ± 2.606, 1.654 ± 1.905 and −0.213 ± 1.754, respectively, for AS supplementation and 1.688 ± 1.426, 1.471 ± 1.425 and −0.217 ± 1.931, respectively, for placebo supplementation. There were no significant differences between AS and placebo supplementation.
Work efficiency during the mental task was measured by the C task of the ATMT. No significant differences were observed between AS and placebo supplementation in both numbers of errors and average response time (data not shown).
Work efficiency during the physical task was measured by the 10-s HPT 0.5 and 3.5 h into the physical task and 3.5 h into the recovery period. Results for AS supplementation were 54.5 ± 21.7 revolutions per minute (rpm), 55.2 ± 19.5 rpm and 56.5 ± 18.8 rpm, respectively. Results for placebo supplementation were 58.3 ± 22.0 rpm, 57.3 ± 20.3 rpm and 59.2 ± 20.7 rpm, respectively. There were no significant differences between AS and placebo supplementation.
The POMS2 and OSA-MA were performed for other subjective feeling assessments. The total mood disturbance in POMS2 was not significantly different between AS and placebo supplementation. OSA-MA evaluation of all five factors was not significant between AS and placebo either before or after four weeks of supplementation, and the change between the two time points was also not different (data not shown).
3.5. Blood Test
PCOOH concentrations are shown in Figure 4
. The plasma astaxanthin level after four weeks of AS supplementation was 208 ± 87 pmol/mL, while that after placebo supplementation was not detectable. During fatigue-inducing tasks, plasma PCOOH levels increased after both AS and placebo supplementation. There was no significant difference between AS and placebo supplementation in the raw data. However, the rate of change of plasma PCOOH levels after AS supplementation was significantly lower than that after placebo supplementation.
The correlation between differences in VAS and plasma astaxanthin concentration was analyzed after AS supplementation for the time point at which a significant difference between the AS group and placebo group was observed. Correlation coefficient between plasma astaxanthin content and the difference in VAS score (recovery 2 h-task 4 h) was −0.451 (p < 0.05), and the difference in VAS score (recovery 4 h-task 4 h) was −0.502 (p < 0.05).
3.6. Safety Evaluation
Among the parameters assessed in general biochemical examinations, several statistically significant changes were observed. However, these were within normal limits of daily variation and were not considered to be due to AS or placebo supplementation by the study doctor. No adverse effects associated with the supplementation were observed.
We evaluated the effect of AS on fatigue in healthy participants aged between 30 and 60. Our results suggest that AS promoted recovery from computer-based mental tasks in subjective fatigue. The subjective fatigue score increased after 4 h of the mental task, then decreased throughout the recovery period after both AS and placebo supplementation. Participants recovered more promptly from VDT-induced mental fatigue (involving a simple working memory task using the two-back test and selective attention and spatial working memory tasks using the ATMT) after four weeks of AS supplementation than after placebo supplementation. A relationship between VDT operation and psychological stress has been shown [37
]. The results of the present study can be generalized to daily fatigue and psychological stress, because the employed tasks were similar to daily VDT operation. The effect of AS on mental status can be extended to brain function-related symptoms, such as depression.
Correlation between plasma astaxanthin concentration and changes in VAS suggest that this anti-fatigue effect of AS might be associated with the effect of astaxanthin. Astaxanthin can cross the blood–brain barrier and protect the brain from acute injury and chronic neurodegeneration [38
]. The neuroprotective properties of astaxanthin are derived from its antioxidative, anti-apoptotic and anti-inflammatory effects [39
]. Antioxidative and anti-apoptotic activity might be attributable to the upregulated expression of endogenous superoxide dismutase and catalase [41
]. An anti-inflammatory mechanism might also be involved in the anti-fatigue effect of astaxanthin, because chicken essence and its dipeptides anserine and carnosine are known to have both anti-inflammatory and anti-fatigue effects [42
]. The link between inflammation and chronic fatigue syndrome has also been reported [44
]. Astaxanthin might therefore be active in the brain under conditions of mental stress to promote recovery from fatigue.
There are several reports of the effects of astaxanthin or sesame-derived compounds after physical exertion [45
]. Astaxanthin has been reported to improve endurance capacity [45
] and fat utilization during exercise via CPT-I activation, leading to improved endurance [46
]. Sesamin may enhance the degradation of lipid peroxides in the liver, resulting in a strong protective effect against exercise-induced plasma lipid peroxidation [47
]. In this study, the effect of AS on physical fatigue could not be evaluated because a carry-over effect from the mental task day was observed. Further investigation is needed to assess the anti-fatigue effect of AS on physical fatigue.
Sesame lignans containing sesamin have been reported to be pro-antioxidant, indirectly acting as an antioxidant via its metabolites [48
]. The supplementation of sesame lignans with vitamin E significantly improved subjective fatigue-related status and antioxidative capacity, particularly in middle-aged and elderly people experiencing feelings of daily fatigue [18
]. The antioxidative [48
], anti-inflammatory and neuroprotective properties of sesamin may contribute to the observed effect of AS. Sesamin exhibited anti-inflammatory activity by inhibiting delta 5-desaturase, which plays an important role in the production of pro-inflammatory mediators [50
]. Excess generation of nitric oxide in lipopolysaccharide-stimulated BV2 microglial cells was significantly attenuated by sesamin [51
]. A neuroprotective effect was also exhibited in gerbil brain in cerebral ischemia [52
]. Sesamin was absorbed efficiently and distributed throughout the whole body, especially in the liver and kidney in the form of its metabolites [21
]. The difference between astaxanthin and sesamin in distribution throughout the body may contribute to the anti-fatigue effect of AS. Further analysis is needed to evaluate the individual effects of sesamin and astaxanthin.
There are several oxidative stress markers including 8-hydroxy-2′-deoxyguanosine, isoprostane and PCOOH. In this study, we chose PCOOH as an oxidative stress marker, since both astaxanthin and sesamin are lipophilic compounds. PCOOH levels reflect the amount of oxidative stress in vivo, as PCOOH is the primary oxidation product of phospholipids [6
]. The relationship between oxidative stress and fatigue has been previously explored [1
], but most of these investigations targeted people with chronic fatigue syndrome. Consistent with previous research, we found that intensive mental and physical tasks increased plasma PCOOH in healthy humans, and AS suppressed the mental and physical task-induced PCOOH increase. Our results suggest that the anti-fatigue effect of AS may be mediated via reduction of oxidative stress. However, further studies to analyze other oxidative stress markers will be needed to reinforce the link between oxidative stress and daily fatigue in healthy humans.
There were several limitations of this study. Sample size was limited, and a per protocol analysis was performed. A carry-over effect of AS was observed due to mental and physical tasks being performed on two consecutive days. Therefore, we could not assess the effect of AS on physical task-induced fatigue. The concentration of sesamin in plasma was not evaluated; hence, the relationship between subjective fatigue and sesamin is unknown. PCOOH was not measured separately after each mental and physical task. Because only continuous ingestion of AS was evaluated in this study, it is not possible to determine whether the observed effects were due to continuous ingestion or a single ingestion.