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Bathing Frequency and Onset of Functional Disability Among Japanese Older Adults: A Prospective 3-Year Cohort Study From the JAGES

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Background: While bathing styles vary among countries, most Japanese people prefer tub bathing to showers and saunas. However, few studies have examined the relationship between tub bathing and health outcomes. Accordingly, in this prospective cohort study, we investigated the association between tub bathing frequency and the onset of functional disability among older people in Japan. Methods: We used data from the Japan Gerontological Evaluation Study (JAGES). The baseline survey was conducted from August 2010 to January 2012 and enrolled 13,786 community-dwelling older people (6,482 men and 7,304 women) independent in activities of daily living. During a 3-year observation period, the onset of functional disability, identified by new certification for need of Long-Term Care Insurance, was recorded. Tub bathing frequencies in summer and winter at baseline were divided into 3 groups: low frequency (0-2 times/week), moderate frequency (3-6 times/week), and high frequency (≥ 7 times/week). We estimated the risks of functional disability in each group using a multivariate Cox proportional hazards model. Results: Functional disability was observed in a total of 1,203 cases (8.7%). Compared with the low-frequency group and after adjustment for 14 potential confounders, the hazard ratios (95% confidence intervals) of the moderate- and high-frequency groups were 0.91 (0.75-1.10) and 0.72 (0.60-0.85) for summer and 0.90 (0.76-1.07) and 0.71 (0.60-0.84) for winter. Conclusion: High tub bathing frequency is associated with lower onset of functional disability. Therefore, tub bathing might be beneficial for older people’s health.
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Received June 18, 2018; accepted October 1, 2018; released online October 27, 2018
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Title Page
Title:
Bathing Frequency and Onset of Functional Disability among Japanese Older Adults: A
Prospective 3-year Cohort Study from the JAGES
Authors:
Akio Yagi1, 2, Shinya Hayasaka3, 4, Toshiyuki Ojima4, Yuri Sasaki5, Taishi Tsuji6, Yasuhiro
Miyaguni7, Yuiko Nagamine1, 6, Takao Namiki2, Katsunori Kondo6, 7, 8
1 Graduate School of Medicine, Chiba University
1-8-1 Inohana, Chuo-ku, Chiba City, Chiba 260-8670, Japan
2 Department of Japanese Oriental “Kampo” Medicine, Chiba University
1-8-1 Inohana, Chuo-ku, Chiba City, Chiba 260-8670, Japan
3 Faculty of Human Life Sciences, Tokyo City University
8-9-18 Todoroki, Setagaya-ku, Tokyo 158-8586, Japan
4 Department of Community Health and Preventive Medicine, Hamamatsu University
School of Medicine
1-20-1 Handayama, Higashi-ku, Hamamatsu City, Shizuoka 431-3192, Japan
5 Department of International Health and Collaboration, National Institute of Public
Health
2-3-6 Minami, Wako City, Saitama 351-0197, Japan
6 Center for Preventive Medical Sciences, Chiba University,
1-8-1 Inohana, Chuo-ku, Chiba City, Chiba 260-8670, Japan
7 Center for Gerontology and Social Science, National Center for Geriatrics and
Gerontology
7-430 Morioka-cho, Obu City, Aichi 474-8511, Japan
8 Center for Well-being and Society, Nihon Fukushi University
5-22-35 Chiyoda, Naka-ku, Nagoya City, Aichi 460-0012, Japan
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E-mail addresses:
A. Yagi: yagiakio-chiba@ya3.so-net.ne.jp
S. Hayasaka: hayasakashi@gmail.com
T. Ojima: ojima@hama-med.ac.jp
Y. Sasaki: sasaki.y.aa@niph.go.jp
T. Tsuji: tsuji.t@chiba-u.jp
Y. Miyaguni: y.miyaguni@ncgg.go.jp
Y. Nagamine: yuiko.mail@gmail.com
T. Namiki: tnamiki@faculty.chiba-u.jp
K. Kondo: kkondo@chiba-u.jp
Corresponding author: Akio Yagi
Present address of corresponding author: Graduate School of Medicine, Chiba University,
1-8-1 Inohana, Chuo-ku, Chiba City, Chiba 260-8670, Japan
Short Title: Bathing frequency and onset of functional disability
Number of Tables: 3
Number of Figures: 0
Number of Supplementary Materials: 8
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ABSTRACT 1
Background: While bathing styles vary among countries, most Japanese people prefer 2
tub bathing to showers and saunas. However, few studies have examined the 3
relationship between tub bathing and health outcomes. Accordingly, in this prospective 4
cohort study, we investigated the association between tub bathing frequency and the 5
onset of functional disability among older people in Japan. 6
Methods: We used data from the Japan Gerontological Evaluation Study (JAGES). The 7
baseline survey was conducted from August 2010 to January 2012 and enrolled 13,786 8
community-dwelling older people (6,482 men and 7,304 women) independent in 9
activities of daily living. During a 3-year observation period, the onset of functional 10
disability, identified by new certification for need of Long-Term Care Insurance, was 11
recorded. Tub bathing frequencies in summer and winter at baseline were divided into 3 12
groups: low frequency (0-2 times/week), moderate frequency (3-6 times/week), and 13
high frequency (≥ 7 times/week). We estimated the risks of functional disability in each 14
group using a multivariate Cox proportional hazards model. 15
Results: Functional disability was observed in a total of 1,203 cases (8.7%). Compared 16
with the low-frequency group and after adjustment for 14 potential confounders, the 17
hazard ratios (95% confidence intervals) of the moderate- and high-frequency groups 18
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were 0.91 (0.75-1.10) and 0.72 (0.60-0.85) for summer and 0.90 (0.76-1.07) and 0.71 19
(0.60-0.84) for winter. 20
Conclusion: High tub bathing frequency is associated with lower onset of functional 21
disability. Therefore, tub bathing might be beneficial for older people’s health. 22
23
Key words: tub bathing; functional decline; care; older people; prevention 24
25
26
INTRODUCTION 27
Population aging is a critical issue in most developed and developing countries.1, 2 With 28
a proportion of individuals 65 years or older of 27.8% (in August 2017), Japan has the 29
most aged population in the world.3 This proportion is expected to increase rapidly in 30
the near future.4 A growing number of older people have a functional disability 31
requiring care in daily life, and there are increasingly fewer young people to support 32
them. Therefore, prevention of functional disability is an important issue for public 33
health in Japan and other counties. 34
Although the Japanese have one of the longest life expectancies in the world,4 the 35
reasons for their longevity are not well understood. The Japanese diet5 and social 36
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cohesion6, 7 appear to play some part. Some other aspects of the Japanese lifestyle might 37
also have a protective effect on health. 38
The Japanese prefer to take baths, especially in a bathtub, rather than shower or 39
sauna bathe, not only for cleanliness, but also to feel warm and refreshed and to aid 40
sleep.8, 9 The relationship between bathing and health outcomes has been reported in 41
several studies. In cross-sectional studies, tub bathing frequency was reported to be 42
associated with good sleep quality, low perceived stress, and good self-rated health.10-12 43
Only one longitudinal study in Japan, with a 5-year observational period, has examined 44
this issue,13 finding that tub bathing frequency was inversely associated with the onset 45
of functional disability. However, that study was limited in generalizability because it 46
specifically enrolled outpatients and had a relatively small sample size (n=610). In a 47
large cohort study in Finland, Laukkanen et al14 identified a strong negative association 48
between sauna bathing frequency and cardiovascular and all-cause mortality, although 49
sauna bathing is clearly distinct from tub bathing. 50
Here, we conducted a large prospective cohort study targeting the general 51
population to evaluate the association between tub bathing frequency and the onset of 52
functional disability among Japanese older adults. 53
54
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METHODS 55
Study population and setting 56
We used data from the Japan Gerontological Evaluation Study15 (JAGES). The baseline 57
survey was performed from August 2010 to January 2012. The target population was 58
community-dwelling older adults, aged 65 or older, not certified to need care under 59
Long-Term Care Insurance (LTCI), and living in 18 municipalities in 8 prefectures in 60
Japan. A total of 110,447 randomly selected people were mailed self-report 61
questionnaires asking about their health status, habits, and lifestyle; 72,760 completed 62
questionnaires were returned (response rate, 65.9%). For 69,408 of them (95.4%), we 63
were able to refer to the LTCI database, which contains the information necessary for 64
follow-up. In a randomly selected one-fourth or one-fifth of the questionnaires (the rate 65
varied depending on municipality), participants were asked about bathing habits 66
(n=16,416). We excluded individuals who were not independent in activities of daily 67
living (ADL) (n=896) or missing information on bathing frequency in summer or winter 68
(n=1,734). This left 13,786 individuals (6,482 men and 7,304 women) for analysis; their 69
mean (SD) age was 73.4 (6.0) years. 70
We observed the participants for 3-years from the baseline survey, and recorded the 71
onset of functional disability (defined in the next section), movement out of the 72
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municipality, and death. This information was obtained from the LTCI database after the 73
end of the observational period; this database is maintained by the local authority of 74
each municipality. 75
This study was approved by the human research ethics committee of Nihon Fukushi 76
University (No. 10-05). All individuals enrolled in the baseline survey were informed 77
that their participation in the study was voluntary and that completion and return of the 78
questionnaire indicated their consent to participate. 79
80
Outcome 81
We defined functional disability as being dependent in ADL by physical or cognitive 82
difficulty, which was identified by certification of need for LTCI (including the “need 83
support” level).16-18 The Japanese LTCI was established to improve older people’s 84
welfare by promoting public care. LTCI is a compulsory coverage insurance, and its 85
benefits are obtained by older people when they apply and are certified to need care. 86
The certification is standardized and based on information on the applicant’s ADL 87
gathered by a qualified investigator and on comments from the family physician.18 88
89
Exposure 90
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In the questionnaire, participants were asked, “How many times a week do you take a 91
bath in a bathtub in summer and in winter?” The original question is shown in eFigure 92
1. We divided tub bathing frequencies into 3 groups: low frequency (0-2 times/week), 93
moderate frequency (3-6 times/week), and high frequency (≥ 7 times/week) for both 94
summer and winter.11, 12 95
In the Japanese style of bathing, the water temperature is usually 39-42 °C. Bathers 96
tend to spend 5-15 minutes in the bathtub, soaking deeply up to the shoulder level.19 97
Bathing is usually performed in the late evening.9 Because changes in the seasons are 98
clear in Japan (hot and wet in summer and cold and dry in winter), 20 the associations 99
between bathing and health outcomes were expected to differ among seasons. 100
Therefore, we measured tub bathing frequency separately in summer and winter. 101
102
Covariates 103
In the baseline survey, we recorded participants’ demographic factors (age, sex, and 104
marital status) and asked about socioeconomic status (employment, equivalized income, 105
and years of education), heath-related behaviors (smoking status, alcohol consumption, 106
and body mass index), and self-reported health status (treatment for any disease, 107
physical strength, cognitive function, depression, and instrumental ADL). 108
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These variables were divided into the following categories: age (65-69, 70-74, 75-109
79, 80-84, or ≥ 85 years old), sex (male or female), marital status (married or single), 110
employment status (not employed or employed), equivalized income (≤ 1.99, 2.00-3.99, 111
or ≥ 4.00 million yen/year), years of education (0-9, 10-12, or ≥ 13 years), smoking 112
status (never smoker, former smoker, or current smoker), alcohol consumption 113
(nondrinker or drinker), body mass index (≤ 18.4, 18.5-24.9, or ≥ 25.0 kg/m2), treatment 114
for any disease (without any disease or with any disease), physical strength (normal or 115
low), cognitive function (normal or a decline), depression (not depressed or depressed), 116
and instrumental ADL (independent or dependent). Physical strength and cognitive 117
function were assessed based on the Kihon Checklist,21, 22 which was developed to 118
identify older people who are at risk of functional disability. Depression was assessed 119
by the shorter version of the Geriatric Depression Scale,23 which includes 15 questions, 120
with a cutoff point of ≥ 5 indicating “depressed”. Instrumental ADL was evaluated using 121
the Tokyo Metropolitan Institute of Gerontology Index of Competence,24 which consists 122
of 5 questions; participants who missed ≥ 1 point were regarded as being “dependent”. 123
124
Statistical analysis 125
After describing the baseline characteristics of the study participants, we used a 126
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multivariate Cox proportional hazards model to estimate the risks of functional 127
disability according to tub bathing frequency. In the multivariate-adjusted model, we 128
adjusted for 14 covariates: age, sex, marital status, employment, equivalized income, 129
years of education, smoking status, alcohol consumption, body mass index, treatment 130
for any disease, physical strength, cognitive function, depression, and instrumental 131
ADL. All of these covariates were assumed to be potential confounders. If the 132
information on a covariate was missing, we classed the participant into a “missing” 133
category when performing the analysis. Participants who moved out or died without 134
functional disability were censored. 135
Next, we performed sensitivity analysis in the multivariate-adjusted model, 136
excluding participants whose follow-up period was less than 1 year in order to take 137
account of non-observable risk factors. Subgroup analysis was then performed with 138
stratification by sex, age (65-74 or ≥ 75 years old), and baseline health status, such as 139
treatment for any disease, physical strength, cognitive function, depression, and 140
instrumental ADL. When performing this analysis, we used the variables in the 141
multivariate-adjusted model except for the variable used for the stratification. 142
The proportional hazards assumption was graphically verified by plotting the log [–143
log] transformation of the cumulative survival curve of each exposure group.25 144
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We used SPSS Statistics version 24.0 (IBM Inc., Armonk, NY) for all analyses. A 145
p-value less than 0.05 was considered significant. 146
147
RESULTS 148
Baseline characteristics of the study participants are described in Table 1. The numbers 149
of individuals in each bathing frequency group (low, moderate, and high) were 1,448, 150
2,777, and 9,561 for summer and 1,347, 4,021, and 8,418 for winter, respectively. 151
Compared with the other groups, the people classed in the high-frequency group were 152
younger and more likely to be married, not depressed, and independent in instrumental 153
ADL and have a moderate-to-high equivalized income, normal physical strength, and 154
normal cognitive function. This tendency was clearer in winter than in summer. 155
The total observation time was 36,619 person-years (average, 2.7 years/participant). 156
Of the 13,786 participants, 1,203 cases (8.7%) of functional disability, 90 cases (0.7%) 157
of movement out of the municipality, and 335 cases (2.4%) of death were recorded. The 158
main results of our research are shown in Table 2, with a description of the hazard ratios 159
of each bathing frequency group, analyzed by both crude and multivariate-adjusted 160
models. In the multivariate-adjusted model, compared with the low-frequency group, 161
the hazard ratios (95% confidence intervals) of the moderate- and high-frequency 162
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groups were 0.91 (0.75-1.10) and 0.72 (0.60-0.85) in summer and 0.90 (0.76-1.07) and 163
0.71 (0.60-0.84) in winter. Significant risk reduction was seen in the high-frequency 164
group in both summer and winter. The hazard ratios were almost the same in summer 165
and winter. 166
The results from the sensitivity analysis are shown in Table 3. After the exclusion of 167
individuals whose follow-up period was less than 1 year, the inverse association 168
between bathing frequency and functional disability onset remained consistent. 169
Subgroup analysis results are presented in eTable 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, and 1-7. 170
The results were almost consistent among subgroups. 171
172
DISCUSSION 173
Our main finding is that individuals who frequently took baths in a bathtub were less 174
likely to be functionally disabled after adjustment for potential confounders. A seasonal 175
difference in the association was not seen in the multivariate-adjusted model. The 176
results from the sensitivity analysis weaken the possibility of a reverse-causation bias 177
because potentially vulnerable individuals might be functionally disabled earlier. In 178
addition, the results from the subgroup analysis imply that the association between 179
exposure and outcome is consistent regardless of sex, age, or baseline health status. 180
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Two pathways may explain the association between bathing and older people’s 181
health status. First, tub bathing promotes good sleep26, 27 and decreases sympathetic 182
nerve activity.28 These changes may be beneficial for the mental status of older people 183
and may prevent depression or cognitive function decline. Second, tub bathing raises 184
the body temperature,29 which leads to increased expression of heat shock proteins 185
(HSPs).30 HSPs have cytoprotective, anti-apoptotic, and anti-inflammatory effects.31 186
Additionally, HSPs are believed to play therapeutic roles in type 2 diabetes mellitus32 187
and Alzheimer’s disease.33 Thus, HSPs may improve or maintain the health conditions 188
of older people. In Japan, the direct causes of older people’s functional disability are 189
mainly dementia, cerebrovascular disease, arthrosis, fracture, and malignancy. 34 The 190
relationship between tub bathing and these diseases should be researched in a future 191
study. 192
Our study results are consistent with those obtained in the aforementioned Finnish 193
study,14 which indicated a robust negative association between sauna bathing frequency 194
and cardiovascular and all-cause mortality, as well as several Japanese cross-sectional 195
studies10-12 reporting a positive association between tub bathing frequency and self-rated 196
health, which is a better predictor of functional disability in older people.35, 36 Our 197
results are also consistent with the only Japanese longitudinal study to examine this 198
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issue,13 which found a negative association between tub bathing and functional 199
disability onset, although that study had a smaller sample size than ours and specifically 200
targeted outpatients. 201
Strengths of our work include a large sample size, the enrollment of a general 202
population in different regions in Japan, and the use of appropriate statistical 203
methodology to adequately control for confounders. There are also several limitations. 204
First, the certification of need for care did not always reflect functional disability. 205
However, because this misclassification was expected to occur equally in each exposure 206
group, we might actually have underestimated the association between exposure and 207
outcome.37 Second, because we surveyed only tub bathing frequency, other types of 208
bathing (ie, sauna or shower) were not taken into account, which limits the 209
generalizability of our study when our findings are applied to people living in cultures 210
without tub bathing. These issues should be investigated in a future study. Third, we 211
could not examine the safety or risks of tub bathing in this study design. Sudden death 212
or accidents during bathing are often reported in Japanese society.38, 39 Therefore, safety 213
issues related to tub bathing are important and should be studied appropriately. The 214
relationship between bathing habit and mortality should be researched in a subsequent 215
study, to take account of the risk of bathing-related death. Additionally, if our results are 216
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applied to clinical practice or recommended as an intervention, careful attention should 217
be paid to safety. Considerations include advice for people with fever or excessive 218
hypertension to avoid bathing39 and a reminder that the bathroom and dressing room 219
should be warm.40 Lastly, we could not completely eliminate the reverse-causation bias, 220
even after controlling for confounders and performing sensitivity analysis, because 221
healthier people might bathe more frequently. However, this limitation is inevitable in 222
an observational study. 223
In conclusion, our study indicates that a high frequency of tub bathing is associated 224
with lower onset of functional disability among Japanese older adults. Further studies 225
investigating the mechanisms linking tub bathing and older people’s health are 226
warranted. 227
228
ACKNOWLEDGEMENTS 229
Funding: This study used data from JAGES, which was supported by MEXT (Ministry 230
of Education, Culture, Sports, Science and Technology-Japan) – Supported Program for 231
the Strategic Research Foundation at Private Universities (2009-2013); JSPS (Japan 232
Society for the Promotion of Science) KAKENHI Grant Numbers (JP18390200, 233
JP22330172, JP22390400, JP23243070, JP23590786, JP23790710, JP24390469, 234
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JP24530698, JP24683018, JP25253052, JP25870573, JP25870881, JP26285138, 235
JP26882010, JP15H01972); Health Labour Sciences Research Grants (H22-Choju-236
Shitei-008, H24-Junkanki [Seishu]-Ippan-007, H24-Chikyukibo-Ippan-009, H24-Choju-237
Wakate-009, H25-Kenki-Wakate-015, H25-Choju-Ippan-003, H26-Irryo-Shitei-003 238
[Fukkou], H26-Choju-Ippan-006, H27-Ninchisyou-Ippan-001, H28-choju-Ippan-002); 239
AMED (Japan Agency for Medical Research and Development), the Research Funding 240
for Longevity Sciences from National Center for Geriatrics and Gerontology (24-17, 241
24-23, 29-42); and World Health Organization Centre for Health Development (WHO 242
Kobe Centre)(WHO APW 2017/713981). The views and opinions expressed in this 243
article are those of the authors and do not necessarily reflect the official policy or 244
position of the respective funding organizations. 245
Conflicts of interest: None declared. 246
Author contributions: AY analyzed and interpreted the data and drafted the article. SH, 247
TO, and KK designed the study, interpreted the data, and revised the article. YS, TT, 248
YM, YN, and TN interpreted the data and revised the article. 249
250
251
252
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Living Condition, 2016. https://www.mhlw.go.jp/toukei/saikin/hw/k-tyosa/k-
tyosa16/index.html; 2017 Accessed 18.08.26. (in Japanese)
35. Stuck AE, Walthert JM, Nikolaus T, Bula CJ, Hohmann C, Beck JC. Risk factors
for functional status decline in community-living elderly people: a systematic
literature review. Soc Sci Med. 1999;48:445-69.
36. Hirai H, Kondo K, Ojima T, Murata C. Examination of risk factors for onset of
certification of long-term care insurance in community-dwelling older people:
AGES project 3-year follow-up study. Jpn J Public Health. 2009;56:501-12. (in
Japanese).
37. Wacholder S, Hartge P, Lubin JH, Dosemeci M. Non-differential
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38. Suzuki M, Shimbo T, Ikaga T, Hori S. Sudden Death Phenomenon While
Bathing in Japan - Mortality Data. Circulation Journal. 2017;81:1144-9.
39. Hayasaka S, Haraoka T, Ojima T. Relationship of Bathing Care-related Illness or
Incident with Blood Pressure and Body Temperature: A Case-control Study. J
Balneol Climatol Phys Med. 2016;79:112-8. (in Japanese).
40. Takasaki Y, Nagai Y, Inoue K, Maki M, Ohnaka T, Tochihara Y. Bating habits of
the elderly in winter and factors affecting regional differences in bathing death
rates. Journal of human and living environment. 2011;18:99-106. (in Japanese).
Accepted Version
Table 1. Baseline characteristics of study participants according to the frequency of tub bathing in summer and in winter.
Variables Summer Winter
Frequency of tub bathing (times/week) Frequency of tub bathing (times/week)
0-2 3-6 ≥ 7 0-2 3-6 ≥ 7
n (%) n (%) n (%) n (%) n (%) n (%)
Participants (n) 1448 2777 9561 1347 4021 8418
Age (years)
65-69 469 (32.4) 785 (28.3) 3209 (33.6) 285 (21.2) 1172 (29.1) 3006 (35.7)
70-74 394 (27.2) 820 (29.5) 2766 (28.9) 345 (25.6) 1197 (29.8) 2438 (29.0)
75-79 305 (21.1) 616 (22.2) 2038 (21.3) 331 (24.6) 887 (22.1) 1741 (20.7)
80-84 194 (13.4) 373 (13.4) 1083 (11.3) 256 (19.0) 539 (13.4) 855 (10.2)
≥ 85 86 (5.9) 183 (6.6) 465 (4.9) 130 (9.7) 226 (5.6) 378 (4.5)
Sex
Male 732 (50.6) 1395 (50.2) 4355 (45.5) 699 (51.9) 1806 (44.9) 3977 (47.2)
Female 716 (49.4) 1382 (49.8) 5206 (54.5) 648 (48.1) 2215 (55.1) 4441 (52.8)
Marital status
Married 911 (62.9) 1798 (64.7) 6880 (72.0) 812 (60.3) 2518 (62.6) 6259 (74.4)
Single 452 (31.2) 850 (30.6) 2341 (24.5) 452 (33.6) 1319 (32.8) 1872 (22.2)
Missing 85 (5.9) 129 (4.6) 340 (3.6) 83 (6.2) 184 (4.6) 287 (3.4)
Employment
Not employed 969 (66.9) 1895 (68.2) 6368 (66.6) 921 (68.4) 2734 (68.0) 5577 (66.3)
Employed 297 (20.5) 511 (18.4) 2069 (21.6) 212 (15.7) 764 (19.0) 1901 (22.6)
Missing 182 (12.6) 371 (13.4) 1124 (11.8) 214 (15.9) 523 (13.0) 940 (11.2)
Equivalized income (million
yen/year)
Low (≤ 1.99) 598 (41.3) 1299 (46.8) 3546 (37.1) 619 (46.0) 1820 (45.3) 3004 (35.7)
Middle (2.00-3.99) 428 (29.6) 788 (28.4) 3244 (33.9) 336 (24.9) 1170 (29.1) 2954 (35.1)
High (≥ 4.00) 112 (7.7) 148 (5.3) 1079 (11.3) 70 (5.2) 247 (6.1) 1022 (12.1)
Missing 310 (21.4) 542 (19.5) 1692 (17.7) 322 (23.9) 784 (19.5) 1438 (17.1)
Years of education
0-9 675 (46.6) 1381 (49.7) 4455 (46.6) 720 (53.5) 1941 (48.3) 3850 (45.7)
10-12 453 (31.3) 827 (29.8) 3282 (34.3) 330 (24.5) 1276 (31.7) 2956 (35.1)
≥13 235 (16.2) 438 (15.8) 1499 (15.7) 209 (15.5) 624 (15.5) 1339 (15.9)
Missing 85 (5.9) 131 (4.7) 325 (3.4) 88 (6.5) 180 (4.5) 273 (3.2)
Smoking status
Never smoker 742 (51.2) 1385 (49.9) 5334 (55.8) 669 (49.7) 2154 (53.6) 4638 (55.1)
Former smoker 402 (27.8) 768 (27.7) 2457 (25.7) 346 (25.7) 1040 (25.9) 2241 (26.6)
Current smoker 167 (11.5) 333 (12.0) 888 (9.3) 167 (12.4) 433 (10.8) 788 (9.4)
Missing 137 (9.5) 291 (10.5) 882 (9.2) 165 (12.2) 394 (9.8) 751 (8.9)
Alcohol consumption
Non-drinker 823 (56.8) 1666 (60.0) 6001 (62.8) 851 (63.2) 2475 (61.6) 5164 (61.3)
Drinker 547 (37.8) 939 (33.8) 3039 (31.8) 418 (31.0) 1325 (33.0) 2782 (33.0)
Missing 78 (5.4) 172 (6.2) 521 (5.4) 78 (5.8) 221 (5.5) 472 (5.6)
Body mass index (kg/m2)
≤ 18.4 105 (7.3) 217 (7.8) 616 (6.4) 123 (9.1) 299 (7.4) 516 (6.1)
18.5-24.9 953 (65.8) 1766 (63.6) 6460 (67.6) 833 (61.8) 2595 (64.5) 5751 (68.3)
≥ 25.0 296 (20.4) 631 (22.7) 2049 (21.4) 294 (21.8) 881 (21.9) 1801 (21.4)
Missing 94 (6.5) 163 (5.9) 436 (4.6) 97 (7.2) 246 (6.1) 350 (4.2)
Treatment for any disease
Without any disease 365 (25.2) 612 (22.0) 2242 (23.4) 295 (21.9) 882 (21.9) 2042 (24.3)
With any disease 957 (66.1) 1962 (70.7) 6614 (69.2) 922 (68.4) 2840 (70.6) 5771 (68.6)
Missing 126 (8.7) 203 (7.3) 705 (7.4) 130 (9.7) 299 (7.4) 605 (7.2)
Physical strengtha
Normal 972 (67.1) 1801 (64.9) 6760 (70.7) 808 (60.0) 2652 (66.0) 6073 (72.1)
Low 301 (20.8) 606 (21.8) 1685 (17.6) 344 (25.5) 862 (21.4) 1386 (16.5)
Accepted Version
Missing 175 (12.1) 370 (13.3) 1116 (11.7) 195 (14.5) 507 (12.6) 959 (11.4)
Cognitive functionb
Normal 836 (57.7) 1605 (57.8) 5964 (62.4) 727 (54.0) 2390 (59.4) 5288 (62.8)
Decline 519 (35.8) 992 (35.7) 2991 (31.3) 525 (39.0) 1376 (34.2) 2601 (30.9)
Missing 93 (6.4) 180 (6.5) 606 (6.3) 95 (7.1) 255 (6.3) 529 (6.3)
Geriatric depression scale
0-4 (not depressed) 798 (55.1) 1559 (56.1) 6034 (63.1) 686 (50.9) 2245 (55.8) 5460 (64.9)
5-15 (depressed) 392 (27.1) 765 (27.5) 1962 (20.5) 420 (31.2) 1075 (26.7) 1624 (19.3)
Missing 258 (17.8) 453 (16.3) 1565 (16.4) 241 (17.9) 701 (17.4) 1334 (15.8)
Instrumental ADLc
Independent 1051 (72.6) 2015 (72.6) 7201 (75.3) 893 (66.3) 3026 (75.3) 6348 (75.4)
Dependent 294 (20.3) 576 (20.7) 1774 (18.6) 350 (26.0) 744 (18.5) 1550 (18.4)
Missing 103 (7.1) 186 (6.7) 586 (6.1) 104 (7.7) 251 (6.2) 520 (6.2)
ADL, activities of daily living.
a Consists of 5 questions on participants' self-reported physical strength. Participants who missed ≥ 3 points were regarded as being "low".
b Consists of 3 questions on participants' self-reported cognitive function. Participants who missed ≥ 1 point were regarded as showing a
"decline".
c Consists of 5 questions on participants' self-reported instrumental ADL, such as use of public transport and management of money. Participants who missed
≥ 1 point were regarded as being "dependent".
Accepted Version
Table 2. Hazard ratios (95% confidence intervals) of functional disability onset according to the frequency of tub bathing in
summer and in winter.
Frequency of tub bathing Crude Model Multivariate-adjusted Modela
(times/week) HR 95% CIs p-value HR 95% CIs p-value
Summer 0-2 reference reference
3-6 1.00 (0.83-1.21) 0.995 0.91 (0.75-1.10) 0.323
≥ 7 0.64 (0.54-0.75) <0.001 0.72 (0.60-0.85) <0.001
Winter 0-2 reference reference
3-6 0.66 (0.56-0.78) <0.001 0.90 (0.76-1.07) 0.246
≥ 7 0.41 (0.35-0.48) <0.001 0.71 (0.60-0.84) <0.001
HR, hazard ratio; CIs, confidence intervals.
a Adjusted for age, sex, marital status, employment, equivalized income, years of education, smoking status, alcohol
consumption, body mass index, treatment for any disease, physical strength, cognitive function, depression, and instrumental
ADL.
Accepted Version
Table 3. Sensitivity analysis. Hazard ratios (95% confidence intervals) of functional
disability onset, after the exclusion of participants whose follow-up period was < 1 year.
Frequency of tub bathing Multivariate-adjusted Modela
(times/week) HR 95% CIs p-value
Summer 0-2 reference
3-6 0.93 (0.73-1.17) 0.517
≥ 7 0.75 (0.61-0.93) 0.007
Winter 0-2 reference
3-6 0.94 (0.76-1.17) 0.592
≥ 7 0.72 (0.59-0.89) 0.002
HR, hazard ratio; CIs, confidence intervals.
a Adjusted for age, sex, marital status, employment, equivalized income, years of education,
smoking status, alcohol consumption, body mass index, treatment for any disease, physical
strength, cognitive function, depression, and instrumental ADL.
... In addition, a previous survey reported that >90% of Japanese people are not satisfied with only taking a shower. 1,2 The main purposes of bathing are relaxation, relieving fatigue, and warming the body, whereas showering is mainly for washing and cleaning the body. 1,3 This custom is also considered essential even at the end of life. ...
... 1,2 The main purposes of bathing are relaxation, relieving fatigue, and warming the body, whereas showering is mainly for washing and cleaning the body. 1,3 This custom is also considered essential even at the end of life. Skaczkowski et al. 4 reported that spa baths improved palliative care patients' self-reported pain, anxiety, and well-being, which may improve quality of life. ...
... This is consistent with the previous reports that Japanese people have a high need for bathing. 1,3,6,[9][10][11]15,16 However, it is often difficult for terminally ill patients, especially in their last month, to bathe independently because of their severe symptoms and decreased ADL, because they require the assistance of two or more nurses to take a bath. 4,11,14,16,22,23 Although there is a high need for bathing even among terminally ill cancer patients, in this study, only 40% (n = 353) of the patients could actually bathe. ...
Article
Background: Bathing in a tub is integral to Japanese culture. It improves palliative care patients' symptoms and may improve quality of life. Objectives: This study aimed to determine the prevalence and impressions of bathing for terminally ill cancer patients and its relations to the evaluations of perceived end-of-life care and achievement of a good death. Design: This was a cross-sectional, anonymous, self-report questionnaire survey. Setting/subjects: The questionnaire for this study was sent to bereaved family members who had lost loved ones in 14 general hospitals and 187 palliative care wards in Japan. Measurements: The bereaved family members of the patients who had actually bathed were asked about their impression of bathing. The short version of the Good Death Inventory (GDI) and the Care Evaluation Scale were used to evaluate "achievement of a good death." In total, 1819 surveys were sent between July and September 2018 to bereaved family members of patients who had died between February 2014 and January 2018 in 14 general hospitals and 187 palliative care wards in Japan. Overall 885 questionnaires (valid response rate 48%) returned by bereaved family members were analyzed. Results: Overall, 85% of bereaved family members of patients who bathed evaluated the experience positively, 86% reported that the patient's face seemed to become calm after the bath, and 28% of bereaved family members whose loved one had not bathed reported regretting it. The total GDI score for the bereaved family's desired death was 82.7 ± 13.0 for the bathing group and 75.4 ± 15.7 for the no bathing group, a significant difference (effect size = 0.52, p < 0.01). Conclusions: Bathing before death was evaluated positively and was associated with the achievement of a good death.
... JSB can also ameliorate sleep disturbances in patients with insomnia [80,81] and dementia [56]. JSB habits appear to have led to improvements in self-rated health [58,59] and depressive symptoms [62,66,67,87]. In an epidemiological study, Aritake-Okada et al. [57] investigated the relationship between daytime sleepiness and coping with regular behavior (having a bath, reading or listening to music, eating and drinking, etc.) to obtain adequate sleep in 24,686 general adults in Japan. ...
... In particular, it was shown that bathing in winter has a great effect of suppressing the onset of depression. Yagi et al. [87] also indicated that a high frequency of tub bathing is associated with lower onset of functional disability including depression among Japanese older adults. Recently, Tai et al. [67] showed interesting results from a logistic regression analysis of JSB habits and depression symptoms. ...
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Japanese-style bathing (JSB), which involves soaking in hot water up to the shoulders in deep bathtubs for a long time in the evening to night, is unique. Many experimental and epidemiological studies and surveys have shown that JSB improve sleep quality, especially shortens sleep onset latency in winter. In addition, repeated JSB lead the improvement of depressive symptoms. JSB is a simple and low-cost non-pharmacological measure to sleep difficulty in winter and mental disorders, especially for the elderly. On the contrary, drowning, while soaking in a bathtub, is the most common of accidental death at home in Japan. It is estimated that approximately 19,000 Japanese individuals die annually while taking a bath, mostly during winter, and most victims are elderly people. Elderly Japanese people tend to prefer a higher-risk JSB because the temperature inside the house during winter, especially the dressing room/bathroom temperature, is very low. Since the physiological thermal effect of the elderly associated with bathing is relatively lower among the elderly than the young, the elderly prefer to take a long hot bath. This elderly’s favorite style of JSB results in larger increased blood pressure in dressing rooms and larger decreased in blood pressure during hot bathing. A sudden drop in blood pressure while immersed in the bathtub leads to fainting and drowning. Furthermore, elderly people are less sensitive to cold air or hot water, therefore, it is difficult to take appropriate measures to prevent large fluctuations in blood pressure. To ensure a safe and comfortable winter bathing, the dressing room/bathroom temperature needs to be maintained at 20 °C or higher, and several degrees higher would be recommended for the elderly.
... These definitions were used in previous epidemiological studies. 18,19 Exposure ...
... We included a wide range of covariates in the analyses as potential confounders based on prior literature. 8,9,12,18,21 Information on sex, age, hypertension, diabetes mellitus, smoking habit, alcohol intake, family structure , social participation, A c c e p t e d V e r s i o n 6 depressive symptoms, cognitive function, instrumental activities of daily living (IADL), educational attainment, and equivalent income was obtained from a self-administered questionnaire. Smoking habit and alcohol intake were classified into the following three categories: current, ever, and never. ...
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Background: While laughter is broadly recognized as a good medicine, a potential preventive effect of laughter on disability and death is still being debated. Accordingly, we investigated the association between the frequency of laughter and onset of functional disability and all-cause mortality among the older adults in Japan. Methods: The data for a 3-year follow-up cohort including 14,233 individuals (50.3% men) aged ≥ 65 years who could independently perform the activities of daily living and participated in the Japan Gerontological Evaluation Study were analyzed. The participants were classified into four categories according to their frequency of laughter (almost every day, 1–5 days/week, 1–3 days/month, and never or almost never). We estimated the risks of functional disability and all-cause mortality in each category using a Cox proportional hazards model. Results: During follow-up, 605 (4.3%) individuals developed functional disability, identified by new certification for the requirement of Long-Term Care Insurance, and 659 (4.6%) deaths were noted. After adjusting for the potential confounders, the multivariate-adjusted hazard ratio of functional disability increased with a decrease in the frequency of laughter (p for trend = 0.04). The risk of functional disability was 1.42 times higher for individuals who laughed never or almost never than for those who laughed almost every day. No such association was observed with the risk of all-cause mortality (p for trend = 0.39). Conclusions: Low frequency of laughter is associated with increased risks of functional disability. Laughter may be an early predictor of functional disability later on in life.
... Yagi et al. showed that a high frequency of bathing (≥7 times/week) was associated with a lower risk of functional disability compared to a low frequency of bathing (0 to 2 times/week) [44]. ...
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... CLHLS also did not collect detailed information on whether the bathing difficulties were experienced only in the winter months or throughout the year, which would have helped to clarify whether there were cyclical effects affecting bathing disability. It is possible that bathing frequency and the types of difficulties faced could differ between the summer and winter seasons (Yagi et al., 2019), and future studies could seek to address that as well. Furthermore, while CLHLS is nationally representative, that is not the case at the regional level, and there could be regional biases. ...
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Bathing is a major type of disability among older adults. While studies on bathing difficulties have recently started to go beyond the limitations of the human body to examine bathroom amenities; researchers have rarely considered the environment beyond the bathroom. This study explored the regional disparities in bathing disability among older adults in China. Using data from the Chinese Longitudinal Healthy Longevity Survey from 1998 to 2018, random-effects logistic regressions were performed to examine how bathing difficulties differed across regions among older adults in China. We found that older adults residing in the northern regions were significantly more likely to experience bathing disability compared to those from the South after controlling for confounding variables. Women and the oldest-old were also the most likely to experience bathing disabilities. Within the Northern regions itself, individuals from the Northeast stood out for having the highest likelihood of experiencing bathing disability. Interestingly, this regional disparity only existed for bathing disability and not the other Activities of Daily Living (ADL) items. It is concluded that the large regional disparity could be due to both climate differences and uneven economic development across the different regions in China. As bathing is a highly environment-dependent activity, this study highlights the potential for policy interventions to reduce the prevalence of bathing disability among older adults through improving the bathing environment. Additionally, we aim to put forth the notion that disability research should move towards analyses of specific disability items rather than an undifferentiated ADL index.
... For Japanese individuals, relaxation is considered a primary objective of bathing in a tub, in addition to cleanliness. 23,24 "Relaxation" refers to the predominant activity of the parasympathetic nervous system, as opposed to excitation of the sympathetic nervous system in the form of a stress response. 17 Previous studies have reported improvements in brain waves, insomnia, and exhaustion in older adults after bathing in a tub; thus, it could be considered that bathing, in terms of relaxation, is effective in improving tiredness. ...
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... Bathing disability has been independently associated with an increased likelihood of long-term nursing home admission [43] and is a primary indicator of the need for home care services [44]. Japanese people generally prefer to take baths rather than taking showers or sauna baths not only for cleanliness but also to feel warm and refreshed as well as to aid in sleep [45]. Morris et al. reported that individuals receiving home care in Hong Kong had the highest rate of grooming disabilities [22]. ...
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... Most Japanese people love deep hot tub bathing (o-furo) rather than showers or saunas. 3 Public opinion surveys have demonstrated that >90% of Japanese people show a preference for taking baths. 4 The average duration of a bath is 25.2 minutes and *80% to 95% of people take a tub bath every day. ...
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Heat therapy, such as sauna and hot tub, has become an increasingly regular therapeutical practice around the world since several studies have shown benefits of heat therapy in metabolic and cardiovascular diseases. The use of heat therapy in people with type 2 diabetes mellitus revealed a striking reduction of 1% unit in the glycated hemoglobin, suggesting this therapy for the treatment of diabetes. Herein, we shall discuss the use of heat therapy and the mechanisms involved, and suggest a provisional guide for the use of heat therapy in obesity and diabetes. Human studies indicate that heat therapy reduces fasting glycemia, glycated hemoglobin, body weight, and adiposity. Animal studies have indicated that nitric oxide and the increase in heat shock protein 70 expression is involved in the improvements induced by heat therapy on insulin sensitivity, adiposity, inflammation, and vasomotricity. Heat therapy is a promising and inexpensive tool for the treatment of obesity and diabetes. We proposed that transient increments in nitric oxide and heat shock protein 70 levels may explain the benefits of heat therapy. We suggest that heat therapy (sauna: 80-100°C; hot tub: at 40°C) for 15 min, three times a week, for 3 months, is a safe method to test its efficiency.
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Aim: The 25-item Kihon Checklist (KCL) is the official self-administered questionnaire tool to screen frail older adults, consisting of seven categories: physical strength, nutritional status, oral function, houseboundness, cognitive function, depression risk and a score of more than 9 out of 1-20 items. The aim of the present study was to evaluate the relationships between each category of the KCL and newly certified cases under the Long-Term Care Insurance (LTCI) in Japan during 24 months. Method: The study population consisted of 883 community-dwelling adults aged 65 years or older uncertified by LTCI completing a questionnaire, which included the KCL and scales of basic/advanced activities of daily living (ADL), quality of life (QOL), and depressive symptoms. The participants were categorized into the risk or non-risk group depending on the official criteria of each KCL category. The outcome was the incidence of newly certified cases by LTCI during 24 months. The difference between the risk and non-risk group was analyzed by Cox regression hazard models. Results: Scores in basic/advanced ADL and QOL were higher, and the score in the geriatric depression scale was lower in the non-risk than the risk group in KCL criteria. In men, the incidence of newly certified cases was higher in the risk group of the physical strength category after adjusting for age and the other categories of the KCL. Conclusion: The physical strength category in men was the only significant predictor of the incidence of newly certified cases by LTCI. Further studies are required to improve the assessment item of cognitive function in KCL under LTCI.