Glycative Stress Research
Online edition : ISSN 2188-3610
Print edition : ISSN 2188-3602
Received : March 27, 2023
Accepted : May 16, 2023
Published online : June 30, 2023
doi:10.24659/gsr.10.2_70

Original article

An observational study for the effects of a hot yoga program in a Wood Stone
Studio on SIRT6 activation.
Yoshikazu Yonei 1), Takahiko Sumi 2), Eri Ito 2), Mio Yamagata 2) Takumi Okada 2)
1) Anti-Aging Medical Research Center and Glycative Stress Research Center,
Graduate School of Life and Medical Sciences, Doshisha University, Kyoto, Japan
2) LAVA International, Tokyo, Japan

Abstract

Purpose: Hot yoga is a practice in which thermotherapy is added to ordinary yoga. A previous study reported a significant
increase in SIRT6 mRNA expression following participation in a twice-weekly, 12-week program, but there was no significant
difference between the regular floor (RF) and Wood Stone Studio (WSS). In the present study, female instructors who
engaged in a hot yoga program for more than 6 months were evaluated and a comparative analysis between RF and WSS wasconducted.
Methods: Subjects were divided into two groups as instructors engaged in a hot yoga program for more than 6 months: 16 in
the WSS group (29.7 ± 1.4 years, BMI: 35.7 ± 0.9) and 19 in the RF group (28.1 ± 0.8 years, BMI: 37.1 ± 0.9). The assessment
items were the Anti-Aging Quality of Life Common Questionnaire (AAQOL), body composition, blood SIRT6 expression
level, and natural killer (NK) cell activity, and multiple regression analysis was performed with SIRT6 expression level as theobjective variable.
Results: AAQOL showed that the WSS group tended to have less "muscle pain and stiffness," "anorexia," and "joint pain"
than RF group (p < 0.1); SIRT6 expression and NK cell activity were not significantly different between two groups. Multiple
regression analysis extracted age and BMI as factors lowering SIRT6 expression (p < 0.05) and WSS as a factor tending toactivate ( p < 0.1).
Conclusion: The results suggest that the use of WSS may add some additional positive effects to the effect of hot yoga on
SIRT6 expression. Further validation of the mechanism of action is needed.

KEY WORDS: hot yoga, sirtuin, SIRT6, natural killer ( NK) cells, body composition

Introduction

Hot yoga is a combination of ordinary yoga andthermotherapy. Since there has been insufficient informationon the effects of hot yoga on the body, two clinical trials 1, 2)
were conducted. The studies focused on telomerase andsirtuin activity as aging-related markers.
In the first clinical trial, 48 healthy Japanese women(39.2 ± 8.7 years) were subjected to 60-minute hot yoga
lessons twice a week for 12 weeks 1). The results showed an
improvement in skin condition after 12 weeks. In addition,
the expression levels of SIRT1, as well as SIRT6, hTERT,
and hTERC in blood were measured by real-time PCR, andthe results showed a significant increase in SIRT6 mRNA
expression.

In the second clinical trial, the subjects for analysis
were healthy women who were aware of their lack of
exercise, and were divided into a control group (n = 19, age
43.6 ± 10.3 years, BMI 26.4 ± 0.8) and a hot yoga group (n= 34, age 44.1 ± 9. 5 years, BMI 25.7 ± 0.4). 60-minute hot
yoga lessons were given twice a week for 12 weeks 2). After
12 weeks, the results showed a significant increase in SIRT6
expression of HbA1c in the hot yoga group compared to thecontrol group. Again, SIRT1, SIRT6, hTERT, and hTERC
expression were measured, but only SIRT6 expression was
found to be elevated. Furthermore, the hot yoga practitioners
were divided into two groups, a wood stone studio (WSS)
group and a regular floor (RF) group (n = 17 each), and two

Correspondent to: Professor Yoshikazu Yonei, MD, PhD
Anti-Aging Medical Research Center / Glycative Stress Research Center,
Doshisha University Graduate School of Life and Medical Sciences
1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0321 Japan
TEL&FAX: + 81-774-65-6394 e-mail: yyonei@mail.doshisha.ac.jp
Co-authors; Sumi T, monitor@yoga-lava.com; Ito E, e-ito@lava-intl.co.jp;
Yamagata M, mio.yamagata@lava-intl.co.jp; Okada T, takumi.okada@lava-intl.co.jp_ 70 _

Glycative Stress Research 2023; 10 (2): 70-78(c) Society for Glycative Stress ResearchGlycative Stress Researchgroups were compared. The results showed that there was no
significant difference in SIRT6 activity between two groups,
but in WSS group, the skin stratum corneum water content wassignificantly improved, and blood tests showed that a decreasein RBC and Hb was avoided, total protein was significantly
increased, and CPK was slightly elevated.
In the current study, hot yoga instructors working for atleast 6 months were divided into two groups, those working at
WSS and those working at RF, and physical/mental symptoms,
body composition, natural killer (NK) cell activity, and SIRT6
expression were measured, and multiple regression analysis
was performed for factors affecting SIRT6 expression.

MethodSubjects

Subjects were female instructors affiliated with LAVA
and working for at least 6 months at facilities with WSS
or with RF, who met the selection criteria, did not meetthe exclusion criteria, and were judged by the principal
investigator to be eligible to participate in the study. Fromthe subjects who met the selection criteria, did not violate
the exclusion criteria, and were judged to be appropriate
to participate in the study by the principal investigator,
16 subjects (29.7 ± 1.4 years) from WSS facilities and 19
subjects (28.1 ± 0.8 years) from RF facilities were selected,
for a total of 35 subjects.
The selection criteria are as follows:(1) Female instructors affiliated with LAVA and working
at WSS facilities for at least 6 months or working at RF
facilities for at least 6 months.
(2) Healthy and free from chronic physical diseases, including
skin diseases.
(3) Be able to come to the office on the designatedexamination date and take the examination.
(4) Persons who are deemed appropriate by the investigatorto participate in the study.
Exclusion criteria are as follows:(1) Currently receiving drug treatment for any disease.
(2) Patients with a history or current medical history ofmental illness, sleep disorder, diabetes, hypertension,
dyslipidemia, or other serious illness.
(3) Those with a history or current history of serious disordersof the uterus, liver, kidney, heart, lungs, blood, etc.
(4) Persons with a history of taking medication for the
purpose of disease treatment in the past month (excluding
abortive medication for headache, common cold, etc.)(5) Pregnant, lactating, or of child-bearing potential.
(6) Currently participating in another human clinical trial, or
who have not yet completed 3 months of participation inanother human clinical trial.
(7) Other subjects who are judged by the investigator to beinappropriate for this study.

Study design

This study was an observational study. Subjects wereasked to comply with the following management items on the
day before the examination:(1) Visit before the examination. Avoid irregular lifestyle(lack of sleep, binge drinking, eating, etc.) on the day
before the visit.
(2) Alcohol consumption is prohibited on the day before thevisit.
(3) Excessive exercise other than that required by the
instructor on the day before the visit was prohibited.
(4) Fasting from 12 hours prior to the scheduled blood
examination until the end of the examination, and no
intake of anything other than water.
On the day of the visit, subjects underwent physicalmeasurements (height, weight, and body composition), bloodpressure and pulse measurements, blood tests (SIRT6 mRNA
expression level and NK cell activity), Anti-Aging Quality ofLife Common Questionnaire (AAQOL), and an interview by
the physician.

WSS

WSS is a studio in which ore stones are placed undercypress flooring, which is further heated by underfloor
heating. It was designed with the expectation of a relaxing
effect from the phytoncide released from the cypress and an
efficient increase in core temperature from the ore containing"silica" with the potential to emit far infrared rays.

Examination item
SIRT6 expression

Blood samples were collected from subjects in
PAXgene ® RNA vacuum blood collection tubes (Becton,
Dickinson and Co., Franklin Lakes, NJ, USA) and measured
at Immunoanalytical Research Center, Inc. (Okayama, Japan).

NK cell activity

Blood was collected from subjects into NK cell activity
lymphocyte storage containers and measured at LSI Medience
Inc. (Tokyo, Japan). NK cytotoxicity against K-562 cells wasevaluated by 51 Cr release assay.

Body composition measurement

InBody 770K (InBody; Koto-ku, Tokyo) to analyze
body composition (body water content, protein, mineralcontent, body fat), muscle and fat (body weight, muscle mass,lean body mass), obesity index (BMI, body fat ratio), muscle
balance (upper body, lower body, upper/lower body), muscle
mass and development rate by site (right arm, left arm, trunk,right leg and left leg), body water content (extracellular water
ratio), body fat by site (right arm, left arm, trunk, right leg
and left leg), water content by site (right arm, left arm, trunk,right leg, left leg, intracellular/extracellular), basal metabolic
rate, bone mineral amount, somatic cell mass, and skeletal
muscle mass index (SMI).

_ 71 _

Hot Yoga and SIRT6 Activation

Anti-Aging QOL Common Questionnaire (AAQOL)

Using AAQOL 3), subjects were asked to answer thephysical condition (33 questions) and mental symptoms (21questions) on a 5-point scale of "1. Not at all," "2. Almost
none," "3. A little," "4. Moderately," and "5. Highly," as wellas lifestyle (6 questions) in numerical form.

Statistical analysis

Appropriate statistical software such as SAS (SAS 9.4)
or SPSS (Statistics 26) was used for statistical analysis, andcomparisons between the WSS bed group and the RF groupwere performed by means of an unpaired t-test ( F test forequal variance, Student's t test for equal variance, and AspinP values obtained from the Welch's t test were employed. Data
from AAQOL were treated as nonparametric, and MannWhitney's U test was employed. Multiple regression analysis
was performed using Excel statistics (Social Information
Service, Tokyo, Japan). Both were two-tailed tests, with arisk rate of less than 5 % (p < 0.05) judged as a significant
difference and less than 10 % (p < 0.1) as a significant trend.

Ethical standards

In accordance with the ethical principles based on the
Declaration of Helsinki (revised Fortaleza, October 2013)
and the Ethical Guidelines for Medical Research Involving
Human Subjects (partially revised in 2017), the Ethics
Committee for Clinical Studies was held at the "Glycative
Stress Research Association" (Shinjuku-ku, Tokyo) to discussand approve the ethics and validity of the study (GSE 2022005). A clinical trial pre-registration was conducted for thisstudy ( UMIN #000049014).

Results

SIRT6 expression

Table 1 shows 0.957 ± 0.059 for WSS group and 0.895± 0.039 for RF group, with no significant difference between
two groups by the t-test (p = 0.376).

NK cell activity

Table 1 shows 48.65 ± 3.04 for WSS group and 49.93± 3.81 for RF group; no significant difference was foundbetween the groups by t-test (p = 0.804).

Body composition (Table 2)

Muscle mass by region (right arm) was significantly
lower in WSS group than in the RF group (p = 0.023).

AAQOL ( Table 3)

There were no significant differences between WSS
group and RF group, but there were significant trends in"muscle pain and stiffness" (p = 0.096), "anorexia" (p =0.072), and "joint pain" (p = 0.061), all of which tended
to be lower in WSS group than in RF group, indicating thatsymptoms were mild.

Multiple regression analysis with SIRT6 expression
as the objective variable (Table 4)

In this analysis, SIRT6 expression level was definedas the objective variable, and factors that increase SIRT6
expression level were predicted. For explanatory variables,
factors that showed even mild correlation with SIRT6
expression level were selected as candidates, and the optimal
combination was explored using a stepwise method. The
explanatory variables for the first step were age, bodycomposition, blood pressure, length of service, and presenceof WSS. Finally, WSS, age, BMI, right arm development
rate, and body water content (right arm) were defined as
explanatory variables; for WSS, a dummy variable wascreated and transformed to = 2 with WSS and 1 without.
Factors decreasing SIRT6 expression were age (β = − 0.0207,
p = 0.0046) and BMI (β = − 0.0769, p = 0.0039); WSS
showed a tendency to activate SIRT6 expression (β = 0.1076,
p = 0.0996).

Table 1. SIRT6 expression and NK cell activity.
Mean
SIRT6 mRNA expression

NK cell activity (%)

SE

0.957 ± 0.059

WSS
RF

0.895 ± 0.039

WSS

48.65 ± 3.04

RF

49.93 ± 3.81

p value
0.376

0.804

WSS group: n = 16, RF group: n = 19. Analyses by Student’s t test. WSS, Wood Stone Studio; RF,regular floor; NK, natural killer; SE, standard error.

_ 72 _Glycative Stress Research

Table 2. Body component.
Mean
Total Body Water

L

Proteinkg

Mineralskg

Body fat masskg

Weightkg

Muscle masskg

Lean body mass

kg

BMI

kg/m 2

Percent body fat%

Balance (upper body)(lower body)(vertical)
Right arm (muscle mass)(development rate)
Left arm (muscle mass)(development rate)
Trunk (muscle mass)kg%(development rate)kg

Right leg (muscle mass)%(development rate)
Left leg (muscle mass)(development rate)
ECW/ TBW

kg
%
kg

WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF

_ 73 _

27.85
28.92
7.41
7.73
2.713
2.805
11.08
10.57
49.06
50.02
35.73
37.11
37.98
39.45
19.09
19.31
22. 31
21.12
1.1
1.3
1.0
1.0
1.9
1.6
1.636
1.781
91.60
97.49
1.590
1.712
88.91
93.64
16.01
16.79
99.13
101.44
6.162
6.231
109.32108.016.122
6.232
108.61108.010.38420.3821

SE
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±

0.72
0.67
0.19
0.18
0.075
0.071
0.85
0.41
1.48
1.15
0.92
0.86
0.98
0.92
0.49
0.37
1.26
0.61
0.1
0.1
0.0
0.0
0.2
0.2
0.064
0.061
7.57
1.72
0.065
0.065
1.85
1.97
0.41
0.39
1.27
0.97
0.189
0.170
1.91
1.54
0.188
0.172
1.90
1.54
0.00140.0011

p value
0.285
0.231
0.383
0.598
0.608
0.281
0.283
0.723
0.405
0.479
1.000
0.240
0.112
0.028
0.199
0.093
0.183
0.151
0.787
0.593
0.668
0.805
0.224

Hot Yoga and SIRT6 Activation

Table 2. Body component.
Body fat mass
Right arm

Mean
kg
%
kg

Left arm

%
kg

Trunk

%
kg

Right leg%kg

Left leg%

Body water content
Right arm

L

Left arm

L

Trunk

L

Right leg

L

Left leg

L

Intracellular

L

Extracellular

L

Skeletal muscle masskg

Basal metabolic rate

kcal

Bone mineral amountkg

Somatic cell mass

kg

SMI

kg/m 2

SE

WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF

0.70
0.65
78.37
70.90
0.73
0.69
80.95
74.61
4.80
4.64
94.51
91.01
2.00
1.86
87.10
80.80
1.99
1.87
86.64
80.55

±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±

0.06
0.03
6.04
2.76
0.06
0.02
5.94
2.83
0.47
0.24
9.02
4.69
0.13
0.06
5.58
2.90
0.13
0.06
5.52
2.86

WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF

1.271
1.384
1.235
1.332
12.49
13.08
4.806
4.857
4.780
4.860
17.16
17.88
10.69
11.04
20.37
21.31
1190.11222.1
2.248
2.338
24.56
25.59
6.01
6.14

±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±

0.050
0.048
0.051
0.050
0.32
0.31
0.148
0.132
0.148
0.135
0.44
0.42
0.29
0.26
0.57
0.54
21.1
19.8
0.061
0.058
0.62
0.60
0.14
0.11

p value
0.400
0.273
0.496
0.346
0.760
0.721
0.349
0.302
0.390
0.313
0.109
0.189
0.190
0.798
0.691
0.242
0.372
0.244
0.278
0.297
0.240
0.460

WSS group: n = 16, RF group: n = 19. Body component measured by “ In Body”. Analyses by Student’s t test.
WSS, Wood Stone Studio; RF, regular floor; BMI, body mass index; ECW, extracellular water; TBW, total body
water; SMI, skeletal muscle mass index; SE, standard error.

_ 74 _Glycative Stress Research

Table 3. AAQOL.
Physical symptoms
Tired eyeBlurry eyes
Eye pain
Stiff shoulders
Mascular pain / stiffness
Palpitations
Shortness of breath
Tendency to gain weight
Weight los/; thin
Lethargy
No feeling of good healthThirstSkin problems
Anorexia
Early satiety
Epigastralgia
Liable to catch cold
Coughing and sputum
Diarrhea
Constipation
Hair loss
Gray hair
HeadacheDizziness
Tinnitus
Difficulty hearing conversation
LumbagoArthralgia
Edematous
Easily breaking into a sweat

Mean
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
_ 75 _
RF
WSS

2.3
2.9
2.0
1.9
1.4
1.7
3.1
3.2
2.4
2.9
1.3
1.3
1.3
1.3
2.4
2.1
1.7
1.5
1.9
2.4
1.7
2.0
1.8
1.7
2.3
2.5
1.2
1.5
1.6
1.6
1.6
1.6
1.4
1.5
1.6
1.4
1.9
1.9
2.0
2.5
1.4
1.7
1.4
1.3
2.1
2.3
1.4
1.9
1.3
1.6
1.5
1.4
2.4
2.2
1.3
1.6
2.4
2.6
3.3

±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±

SE

p value

0.3
0.3
0.2
0.3
0.2
0.2
0.3
0.2
0.2
0.2
0.2
0.2
0.1
0.1
0.3
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.3
0.2
0.1
0.1
0.2
0.2
0.2
0.2
0.2
0.1
0.2
0.1
0.2
0.2
0.4
0.3
0.2
0.3
0.3
0.1
0.3
0.2
0.2
0.2
0.1
0.2
0.2
0.2
0.3
0.3
0.1
0.1
0.2
0.2
0.3

0.16610.67370.45330.61090.09560.8036
0.57140.29900.40750.13370.30200.66630.72950.07190.82040.8136
0.68810.84870.73210.18260.48500.98110.31220.18160.22650.96550.5325
0.06120.50870.2579Dizziness

1.9
RF
1.3
WSS
Tinnitus
1.6
RF
Hot Yoga and
SIRT6 Activation
1.5
WSS
Difficulty hearing conversation
1.4
RF
2.4
WSS
Lumbago
2.2
RF
1.3
WSS
Arthralgia
1.6
RF
2.4
WSS
Edematous
2.6
RF
3.3
WSS
Easily breaking into a sweat
2.8
RF
1.6
WSS
Frequent urination
1.8
RF
1.4
WSS
Hot flush
1.5
RF
2.4
WSS
Cold skin
2.5
RF

Table 3. AAQOL.

Mental symptoms
Irritability
Easily angered
Loss of motivation
No feeling of happiness
Nothing to look forward to in life
Daily life is not enjoyable
Loss of confidence
Reductance to talk with others
Depressed
Feeling of usefulness
Sallow sleep
Difficulty in falling asleep
Pessimism
Lapse of memory
Inablity to concentrate
Inability to solve problems
Inability to make judgments readily
Inability to sleep because of worries
A sense of tension
Feeling of anxiety for no special reason
Vague feeling of fear

±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±

Mean
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF
WSS
RF

2.1
2.1
1.9
1.7
2.0
1.9
1.3
1.4
1.1
1.3
1.1
1.2
1.3
1.3
1.3
1.3
1.3
1.4
1.2
1.3
2.0
2.2
2.1
2.2
1.7
1.8
1.9
2.1
1.9
1.7
1.6
1.6
1.5
1.8
1.8
1.9
1.9
1.7
1.9
1.7
1.4
1.4

0.2
0.1
0.2
0.2
0.2
0.3
0.3
0.1
0.1
0.2
0.2
0.3
0.3
0.2
0.2
0.2
0.2
0.2
0.3

SE
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±

0.2
0.2
0.2
0.1
0.2
0.2
0.1
0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.2
0.1
0.1
0.3
0.2
0.3
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.3
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2

0.18160.22650.96550.5325
0.06120.50870.25790.61220.98390.9179p value
1.00000.5712
0.69330.91650.31570.50980.67230.83990.9281
0.39390.50500.74230.62570.62410.33960.97030.55580.70730.54170.68170.9838

WSS group: n = 16, RF group: n = 19. Analyses by Mann-Whitney's U test. WSS, Wood Stone Studio; RF,regular floor; AAQOL, Anti-Aging Quality of Life Common Questionnaire; SE, standard error.

_ 76 _Glycative Stress Research

Table 4. Multivariate analysis with SIRT6 mRNA expression as the objective variable.
Partial regression
coefficient (β)

SE

t valuep valueAge− 0.0207

0.0067− 3.0727

0.0046

BMI− 0.0769

0.0245− 3.1383

0.00390.1076

0.06331.70130.0996− 0.0049

0.0 075− 0.6538

0.51840.49770.34151.45750.1557

Variable

WSS (+)
Right arm development rate
Body water content (R)WSS (+); n = 16 using WSS, WSS (−): n = 19 using RF. WSS, Wood Stone Studio; RF, regular floor; BMI,
body mass index; (R), right side, SE, standard error.

Discussion
In our previous studies, we found that SIRT6 expression
increased as well as skin condition and subjective symptoms
improved after 12 weeks of participation in a hot yoga
program 1, 2). Multiple regression analysis of factors affecting
SIRT6 expression showed that age and BMI were factors that
decreased SIRT6 expression. This analysis also showed that
WSS tended to activate SIRT6 expression.
The sirtuin gene family plays an important role in the
homeostasis of body functions. Among them, SIRT6 has
NAD+-dependent histone deacetylase (HDAC) activity,
which is characterized by its weaker deacetylase activity andstronger demyristoylation activity than SIRT1, and should be
regarded as a lysine deacylase 4).
SIRT6 is known to stabilize telomeres 5), regulate thetranscriptional activity of NF-kB 6), and maintain DNA repair
capacity 7). SIRT6-deficient cells are highly susceptible to
DNA damage, and SIRT6-knockout mice are highly
susceptible to DNA damage.
SIRT6 knockout mice are short-lived, have decreased
leukocyte counts and bone density, and SIRT6-deficient
cells are highly susceptible to DNA damage 7). Proximal
tubule-specific SIRT6 knockout mice have a type 4 collagendeposition and elicit a phenotype similar to that of diabetic
tubular damage 8). SIRT6 has attracted attention as atherapeutic target for diabetes 9), non-alcoholic steatohepatitis(NASH) 10) and other hepatic metabolic diseases 11), skinwound healing 12), cardiac diseases 13), cancer 14), and early
aging syndrome 15).
Physical exercise 16) has been known as a lifestyle habitthat activates SIRT6 in humans. As a result of this study andprevious studies 1, 2), we can say that hot yoga has newly been
added to the list of SIRT6 activators.
In order to verify the quality improvement of hot yoga,
this study compared the results of WSS and RF. The premiseis that SIRT6 activation is observed with hot yoga in both
WSS and RF. In a previous study 2), the WSS group wassuperior to the RF group in a comparison between the groups
in terms of improvement in skin moisture content. However,the 12-week hot yoga program showed no significant
difference in changes in SIRT6 activity between two groups.
In the present study, instructors who had been engaged
in a hot yoga program for at least 6 months were compared

between two groups. The results showed that multiple
regression analysis identified age and BMI as negative
factors (p < 0.05, significant difference) that decreased SIRT6
activity, and WSS as a positive factor (p < 0.1, significant
trend) that tended to increase SIRT6 activity, suggesting that
WSS may be more beneficial for both program participants
and instructors.

SIRT6 and NK cells

NK cells account for 10 -30 % of lymphocytes in the
blood and are immune response cells that play an importantrole in innate immunity. In vivo, NK cell activity varies withcircumstances, and it is known that aging, smoking, andphysical and mental stress reduce NK cell activity. WhenNK cells detect changes in antigens presented on the surfaceof cancer cells or virus-infected cells (loss of MHC class I
antigen indicating "self " or presence of antigen indicating"not- self " ), the active type receptors on NK cells areactivated and attack the cells by cytokine secretion. WhenNK cells encounter normal cells, signals from inhibitory
receptors predominate and they do not attack the normal
cells.
When the regulatory mechanisms of NK activity are outof balance, they are involved in pathogenesis. In patients withrheumatoid arthritis (RA), an excess of CD38+ NK cells inthe blood is involved in the development and progression of
joint lesions 17). NK/T-cell lymphoma (NKTCL), a rare tumor
among non-Hodgkin's lymphomas, has increased SIRT6
expression 18). This increased SIRT6 expression may be
responsible for the intense aggressiveness of NKCTL cells.
CD38 is a single-transmembrane type II glycoprotein
and is widely used as a cell differentiation marker for
lymphocyte 19). CD38 hydrolyzes NAD to ADP-ribose andcyclic ADP-ribose. As a result, NAD is reduced, resulting
in decreased responsiveness (down-regulation) of SIRT6 20).
Decreased responsiveness of SIRT6 increases the expressionof NKG2D ligand, which in turn increases the expression ofcytokines 21). CD38 is a key component of the NAD-regulated
SIRT6 receptor, which is a key component of the NKG2D
receptor.
Cyanidin-3-O-glucoside (C3G), a natural inhibitor of
CD38, decreases CD38 expression and increases SIRT6
expression 20). C3G decreases cytokine levels such as IL-1β,_ 77 _

Hot Yoga and SIRT6 Activation

IL-6, IL-17A, and TNF-α and restores NAD+ and NK celllevels NAD+ and NK cell levels.
On the other hand, in the case of age-related decline
in NK cell function, it is accompanied by decreased SIRT6
expression 20, 21). Therefore, it is speculated that restoring
SIRT6 activity will lead to the recovery of NK cell function.
In this study, NK cell activity was measured, but there
was no significant difference between WSS group and RF
group. The reason for this is that there was no significant
difference in SIRT6 activity between two groups. The
target instructors were a healthy population, with an age ofaround 30 years and no lifestyle habits that would reduce
NAD reduction due to excess aldehydes (impaired glucose
tolerance, high-fat diet, and excessive alcohol consumption).
Therefore, there was little age-related decline in SIRT6
and little room for improvement in SIRT6. If a clinical
trial is planned in the future to extract differences in NK
cell activity between WSS group and RF group, it could benecessary to recruit subjects with suspected NAD deficiency,
where sufficient room for improvement of SIRT6 can be
expected.

Conclusions

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Two clinical trials have been conducted on hot yoga andconfirmed that participation in the program twice a week for
12 weeks significantly increases SIRT6 mRNA expression.
There was no difference in SIRT6 activity when compared to
WSS and RF. In this study, multiple regression analysis was
performed on female instructors who had been engaged in a
hot yoga program for more than 6 months, and the presenceof WSS was extracted as a factor that tended to increase
SIRT6 activity, and the subjective symptoms of "muscle pain
and stiffness," "loss of appetite," and "joint pain" were lesssevere in WSS group, suggesting that hot yoga using WSS
has some positive effects. This suggests that hot yoga with
WSS may have some positive effects. The mechanism of thiseffect may need to be verified in the future.

Conflict of interest declaration
LAVA International provided support for the conductof this study.

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