Social determinants of health associated with underweight among middle-aged Japanese men and women: a cross-sectional study†

Factors	Underweight (n = 59)	Normal weight (n = 1111)	P-value
BMI (kg/m²)	17.6 (0.8)	22.2 (1.7)	–
Age (years)	53.2 (5.7)	52.5 (6.7)	0.384
Economic status			0.286
Very good or good	10.2	15.7
Average	16.9	21.4
Poor or very poor	72.9	62.9
Education level			0.284
>12 years	50.8	43.7
9–12 years	49.2	56.3
Health literacy (CCHL scale score)	3.5 (0.8)	3.4 (0.8)	0.765
Living alone			<0.001
No	67.8	85.0
Yes	32.2	15.0
Daily working hours*	7.3 (4.5)	8.4 (4.3)	0.059
Smoking status			0.049
Nonsmoker or ex-smoker	47.5	60.3
Current smoker	52.5	39.7
Drinking status			0.679
Nondrinker or occasional drinker	54.2	57.0
Daily drinker	45.8	43.0
Regular exercise			0.672
Yes	35.6	38.3
No	64.4	61.7
Sleep quality			0.499
Restorative sleep	57.6	62.0
Non-restorative sleep	42.4	38.0
Self-reported mental health			0.001
Very good or good	16.9	39.8
Average	52.6	41.8
Poor or very poor	30.5	18.4

Note: Continuous data were analyzed with a t-test and are shown as mean (standard deviation); dichotomous and categorical data were analyzed with the chi-square test and are shown as %; BMI, body mass index; CCHL, Communicative and Critical Health Literacy;

* Includes time for work, housework, childcare, and nursing care.

Table 2.

Differences in factors between the underweight and normal weight groups among middle-aged Japanese women.

Factors	Underweight (n = 242)	Normal weight (n = 1387)	P-value
BMI (kg/m²)	17.4 (1.0)	21.3 (1.7)	–
Age (years)	53.6 (6.7)	54.0 (6.7)	0.421
Economic status			0.157
Very good or good	18.2	23.2
Average	22.7	23.6
Poor or very poor	59.1	53.2
Education level			0.903
>12 years	52.5	52.1
9–12 years	47.5	47.9
Health literacy (CCHL scale score)	3.5 (0.8)	3.6 (0.7)	0.447
Living alone			0.650
No	88.8	87.8
Yes	11.2	12.2
Daily working hours*	8.8 (5.5)	9.3 (5.7)	0.174
Smoking status			0.016
Nonsmoker or ex-smoker	77.7	84.0
Current smoker	22.3	16.0
Drinking status			0.259
Nondrinker or occasional drinker	78.9	82.0
Daily drinker	21.1	18.0
Regular exercise			0.680
Yes	29.3	28.0
No	70.7	72.0
Sleep quality			0.185
Restorative sleep	55.4	59.9
Non-restorative sleep	44.6	40.1
Self-reported mental health			0.198
Very good or good	35.5	38.0
Average	39.3	41.9
Poor or very poor	25.2	20.1

* Includes time for work, housework, childcare, and nursing care.

Table 3.

Multivariable-adjusted RR and 95% CIs for underweight according to different factors among middle-aged Japanese men.

Factors	RR (95% CI)	Multivariable-adjusted RR (95% CI)
Age (years)	1.01 (0.98–1.05)	1.00 (0.97–1.04)
Economic status
Very good or good	1.00	1.00
Average	1.21 (0.45–3.27)	1.02 (0.38–2.77)
Poor or very poor	1.74 (0.75–4.02)	1.29 (0.54–3.09)
Education level
>12 years	1.00	1.00
9–12 years	0.76 (0.46–1.25)	0.61 (0.37–1.03)
Health literacy (CCHL scale score)	1.05 (0.76–1.45)	1.18 (0.84–1.66)
Living alone
No	1.00	1.00
Yes	2.51 (1.49–4.24)	1.97 (1.16–3.36)
Daily working hours *	0.95 (0.89–1.01)	0.95 (0.89–1.01)
Smoking status
Nonsmoker or ex-smoker	1.00	1.00
Current smoker	1.64 (0.99–2.69)	1.75 (1.04–2.95)
Drinking status
Nondrinker or occasional drinker	1.00	1.00
Daily drinker	0.90 (0.55–1.48)	0.85 (0.51–1.43)
Regular exercise
Yes	1.00	1.00
No	0.89 (0.53–1.50)	1.02 (0.61–1.71)
Sleep quality
Restorative sleep	1.00	1.00
Non-restorative sleep	0.84 (0.51–1.39)	0.96 (0.57–1.62)
Self-reported mental health
Very good or good	1.00	1.00
Average	2.83 (1.40–5.70)	2.51 (1.21–5.19)
Poor or very poor	3.66 (1.72–7.81)	3.05 (1.36–6.87)

Note: Log binomial regression models were used to estimate the RRs and 95% CIs for underweight (response variable: 1 = underweight and 0 = normal weight); CCHL, Communicative and Critical Health Literacy; CI, confidence interval; RR, risk ratio;

* Includes time for work, housework, childcare, and nursing care.

Table 4.

Multivariable-adjusted RR and 95% CIs for underweight according to different factors among middle-aged Japanese women.

Factors	RR (95% CI)	Multivariable-adjusted RR (95% CI)
Age (years)	0.99 (0.98–1.01)	0.99 (0.98–1.01)
Economic status
Very good or good	1.00	1.00
Average	1.20 (0.83–1.73)	1.18 (0.81–1.71)
Poor or very poor	1.35 (0.99–1.85)	1.28 (0.91–1.79)
Education level
>12 years	1.00	1.00
9–12 years	0.99 (0.78–1.24)	0.91 (0.72–1.16)
Health literacy (CCHL scale score)	0.94 (0.80–1.10)	0.97 (0.82–1.15)
Living alone
No	1.00	1.00
Yes	0.92 (0.63–1.33)	0.87 (0.60–1.26)
Daily working hours *	0.98 (0.96–1.01)	0.98 (0.95–1.01)
Smoking status
Nonsmoker or ex-smoker	1.00	1.00
Current smoker	1.41 (1.07–1.85)	1.33 (0.99–1.77)
Drinking status
Nondrinker or occasional drinker	1.00	1.00
Daily drinker	0.85 (0.64–1.13)	0.87 (0.66–1.16)
Regular exercise
Yes	1.00	1.00
No	1.06 (0.82–1.36)	1.10 (0.85–1.43)
Sleep quality
Restorative sleep	1.00	1.00
Non-restorative sleep	0.85 (0.68–1.08)	0.87 (0.67–1.12)
Self-reported mental health
Very good or good	1.00	1.00
Average	1.00 (0.76–1.31)	0.94 (0.71–1.24)
Poor or very poor	1.28 (0.95–1.73)	1.11 (0.80–1.56)

* Includes time for work, housework, childcare, and nursing care.

References

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DOI: https://doi.org/10.2478/fon-2026-0035 | Journal eISSN: 2544-8994 | Journal ISSN: 2097-5368

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Language: English

Page range: 309 - 316

Submitted on: Oct 28, 2025

Accepted on: Nov 6, 2025

Published on: Sep 25, 2026

Published by: Shanxi Medical Periodical Press

In partnership with: Paradigm Publishing Services

Keywords:

Japan,

mental health,

middle-aged adults,

social determinants of health,

underweight

Related subjects:

Medicine,

Assistive professions, nursing

© 2026 Akiko Morimoto, Hideaki Furuki, Aina Muta, Liqian Sun, Nao Sonoda, published by Shanxi Medical Periodical Press
This work is licensed under the Creative Commons Attribution 4.0 License.

Volume 13 (2026): Issue 3 (September 2026)