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Table 1 Japanese studies dealing with factors that influence the duration of breastfeeding

From: Infant feeding practices and breastfeeding duration in Japan: A review

Factors Authors (Year) Study design Sample size (n) Definition of breastfeeding Exclusive Breastfeeding rate (%) Crude OR (95% CI) (subgroup) Adjusted OR (95% CI) (subgroup) Study details
Maternal age Kaneko et al. (2006) [20] Cross-sectional 45,569 1. Breastfed 22.4 at 6m 1.2 (1.14,1.26) (30-39 years old) 0.89 (0.84,0.94) (30-39 years old) Mothers who are between 20-29 years old = 1 (reference)
2. Only colostrum
3. Not breastfeed
Yokoyama et al. (2006) [21] Cross-sectional 15262 1. Breastfeeding only N/A N/A N/A  
2. Mixed-feeding (mainly breast with some bottle or mainly bottle with some breast)
3. Bottle feeding with formula milk only
Otsuka et al. (2008) [22] Cross-sectional 262 1. Exclusive Breastfeeding (i.e. breastmilk only) 40 at 4wks 5.37 (1.18,24.40) N/A  
2. Partial breastfeeding (i.e. breastmilk and formula)
3. Bottle-feeding (i.e. no breastmilk at all)
Sasaki et al (2009) [23] Longitudinal 908 1. Only breastfeeding 27.6 at 3-4m N/A N/A Not statistically significant (p = 0.93)
2. Breastmilk and infant formula
3. Only infant formula
Marital status Otsuka et al. (2008) [22] Cross-sectional 262 1. Exclusive Breastfeeding (i.e. breastmilk only) 40 at 4wks N/A N/A Not statistically significant (p = 0.88)
2. Partial breastfeeding (i.e. breastmilk and formula)
3. Bottle-feeding (i.e. no breastmilk at all)
Socioeconomic status Kaneko et al. (2006) [20] Cross-sectional 45,569 1. Breastfed 19 at 6m (< 3.9 million yen) 22 at 6m (> 8.0 million yen) 0.85 (0.80,0.90) (< 3.9 million yen) 1.03 (0.97,1.08) (> 8.0 million yen) 0.93 (0.88,0.99) (< 3.9 million yen) 1.03 (0.97,1.09) (> 8.0 million yen) 4.0-7.9 million yen of annual income = 1 (reference)
2. Only colostrum
3. Not breastfeed
Otsuka et al. (2008) [22] Cross-sectional 262 1. Exclusive Breastfeeding (i.e. breastmilk only) 40 at 4wks 1.0 (0.26,3.55) (>2,000,000 yen) N/A Not statistically significant (p = 0.96)
2. Partial breastfeedin (i.e. breastmilk and formula)
3. Bottle-feeding (i.e. no breastmilk at all)
Educational status Otsuka et al. (2008) [22] Cross-sectional 262 1. Exclusive Breastfeeding (i.e. breastmilk only) 40 at 4wks 1.3 (0.66,2.49) (High school or less) N/A Not statistically significant (p = 0.47)
2. Partial breastfeeding (i.e. breastmilk and formula)
3. Bottle-feeding (i.e. no breastmilk at all)
Maternal employment status Kaneko et al. (2006) [20] Cross-sectional 45,569 1. Breastfed 25.0 at 6m 1.17 (1.09,1.26) (Full time and child care leave for 6m or more) 1.14 (1.05,1.23) (Full time and child care leave for 6m or more) Non-workers = 1 (reference)
  2. Only colostrum
3. Not breastfeed
Sasaki et al. (2009) [23] Longitudinal 908 1. Only breastfeeding 27.6 at 3-4m N/A N/A Not statistically significant (p = 0.12)
2. Breastmilk and infant formula
3. Only infant formula
Multiple births Kaneko et al. (2006) [20] Cross-sectional 46,569 1. Breastfed 1.3 at 6m 0.05 (0.03,0.09) 0.07(0.04,0.12) Single birth = 1 (reference)
2. Only colostrum
3. Not breastfeed
Yokoyama et al. (2006) [21] Cross-sectional 15,262 1. Breastfeeding only N/A N/A N/A Multiple births was associated with breastfeeding cessation (adjusted OR = 0.07, 95% CI = 0.04,0.12)
2. Mixed-feeding (mainly breast with some bottle or mainly bottle with some breast)
3. Bottle feeding with formula milk only
Ooki (2008) [24] Cross-sectional 4,023 1 Full breastfeeding 6.6 at 6m
(Full breastfeeding)
N/A N/A Sample were mother who had twin. Any Breastfeeding and formula feeding at 6m were 36.1 and 54.1%, respectively
2. Partial breastfeeding (mixed feeding)
3. Formula feeding
Maternal smoking status Kaneko et al. (2006) [20] Cross-sectional 46,324 1. Breastfed 11.5 at 6m 0.40 (0.31,0.95) 0.44 (0.34,0.57) Nil smoking of the mothers and fathers = 1 (reference)
2. Only colostrum
3. Not breastfeed
Sasaki et al.
(2009) [23]
Longitudinal 908 1. Only breastfeeding 27.6 at 3-4m N/A N/A Not statistically significant (p = 0.25)
2. Breastmilk and infant formula
3. Only infant formula
Delivery methods Nakao et al. (2008) [25] Cross-sectional 318 1. Fully breastfeeding (breastmilk was given and infant formula was not given, regardless of whether other liquids and/or solid food were given) N/A N/A 1.02 (0.41,2.59) Not statistically significant (p = 0.96)
2. Any Breastfeeding (breastmilk and infant formula were given regardless of whether other liquids and/or solid food were given)
3. Infant formula feeding (formula was given and breast milk was not given regardless of whether other liquids and/or solid food were given)
Sasaki et al. (2009) [23] Longitudinal 908 1. Only breastfeeding N/A N/A N/A Not statistically significant (p = 0.14 for chi square test)
2. Breastmilk and infant formula
3. Only infant formula
Parity Kaneko et al. (2006) [20] Cross-sectional 45,569 1. Breastfed 24.5 at 6m (Second times) 26.1at 6m (Third times or more) 1.57 (1.49,1.65) (Second times) 1.71 (1.60-1.81) (Third times or more) 1.72 (1.63,1.81) (Second times) 2.06 (1.91-2.22) (Third times or more) Primipara = 1 (reference)
3. Not breastfeed
2. Only colostrum
Otsuka et al. (2008) [22] Cross-sectional 262 1. Exclusive Breastfeeding (i.e. breastmilk only) 40 at 4wks N/A N/A Not statistically significant (p = 0.90)
2. Partial breastfeeding (i.e. breastmilk and formula)
3. Bottle-feeding (i.e.no breastmilk at all)
Sasaki et al. (2009) [23] Longitudinal 908 1. Only breastfeeding N/A N/A N/A Not statistically significant (p = 0.55)
2. Breastmilk and infant formula
3. Only infant formula
Current intake of alcohols Sasaki et al. (2009) [23] Longitudinal 908 1. Only breastfeeding N/A N/A 1.37 (1.02,1.86) Not intake of alcohols = 1 (reference) (p = 0.04)
2. Breastmilk and infant formula
3. Only infant formula
Early initiation of breastfeeding Nakao et al. (2008) [25] Cross-sectional 318 1. Fully breastfeeding (breastmilk was given and infant formula was not given, regardless of whether other liquids and/or solid food were given) N/A N/A 2.45 (1.21,4.95) Initiating breastfeeding within 120 minutes after birth was positively associated with duration of breastfeeding at 4 months (p = 0.01)
2. Any Breastfeeding (breastmilk and infant formula were given regardless of whether other liquids and/or solid food were given)
3. Infant formula feeding (formula was given and breast milk was not given regardless of whether other liquids and/or solid food were given)
Intention to breastfeed Nakamura et al. (2002) [26] Cross-sectional 105 1. Breastfeeding 73.9 at 3m N/A N/A  
2. Breast & Bottle feeding
3. Artificial milk
Otsuka et al. (2008) [22] Cross-sectional 262 1. Exclusive Breastfeeding (i.e. breastmilk only) 40 at 4wks N/A N/A Intention to Exclusive Breastfeeding = 1 (reference)
2. Partial breastfeeding (i.e. breastmilk and formula)
   3. Bottle-feeding (i.e. no breastmilk at all)
Maternal attachment Sasano et al. (2005) [27] Cross-sectional 182 1. Breastfeeding 53.4 at 3m N/A N/A  
2. Mix and infant formula feeding
Breastmilk insufficiency Yoshitome et al. (2003) [28] Cross-sectional 246 1 Breastfeeding only 38.5 at 3-4m N/A N/A  
2. Mix feeding
3. Infant formula only
Low birth weight Kaneko et al. (2006) [20] Cross-sectional 46,557 1. Breastfed 11.4 at 6m 0.46 (0.42,0.51) 0.67 (0.60,0.76) ≥ 2500g =1 (reference)
2. Only colostrum
3. Not breastfeed
Maternal confidence Awano et al. (2010) [29] quasi-experimental 117 1 Fully breastfeeding (no formula was given) 72.2 at 4 wks
(Full breastfeeding)
N/A N/A Breastfeeding self-care program is effect to improve maternal confidence
Otsuka et al. (2008) [22] Cross-sectional 262 1. Exclusive Breastfeeding (i.e. breastmilk only) 40 at 4wks N/A N/A Maternal confidence level is related to their perception of insufficient breast milk flow.
2. Partial breastfeeding (i.e. breastmilk and formula)
3. Bottle-feeding (i.e.no breastmilk at all)
Sucking difficulty Yokoyama et al. (2006) [21] Cross-sectional 15,262 1. Breastfeeding only N/A N/A N/A Infants with poor sucking ability are 1.56 times more like to be given infant formula (95% CI = 1.12,2.18)
2. Mixed-feeding (mainly breast with some bottle or mainly bottle with some breast)
3. Bottle feeding with formula milk only
Support from health professionals Sasaki et al. (2009) [23] Longitudinal 908 1. Only breastfeeding N/A N/A 0.83 (0.61,1.12) (Midwives) Without support from midwives = 1 (reference) (p = 0.83)
2. Breastmilk and infant formula
3. Only infant formula
Kaneko et al. (2006) [20] Cross-sectional 45,569 1. Breastfed 29.7 at 6m 1.63 (1.50,1.78) 1.76 (1.60,1.94) Advice on child care from birth attendant/nurse
2. Only colostrum
3. Not breastfeed
Support from husbands/partners Kaneko et al. (2006) [20] Cross-sectional 45,569 1. Breastfed 21.8 at 6m 1.28 (1.21,1.37) 1.07 (1.00,1.14) Support = advice on child care from husbands. No advice =1 (reference)
2. Only colostrum
3. Not breastfeed
Ninomiya et al. (1997) [30] Cross-sectional 264 1. Breastfeeding but exclusion of mix breastfeeding 37.5 at 3m N/A N/A Father’s attendance to an antenatal class is correlated to full breastfeeding duration (p < 0.01).
Ninomiya et al. (1995) [31] Cross-sectional 719 1. Breastfeeding but exclusion of mix breastfeeding N/A N/A N/A Father’s involvements in childcare are associated with full breastfeeding duration for three months postpartum (p < 0.05).
Family smoking environment Kaneko et al. (2006) [20] Cross-sectional 45,569 1. Breastfed 22.6 0.90 (0.86,0.95) 0.92 (0.88,0.97) Non-smoking fathers and mothers = 1 (reference)
2. Only colostrum
3. Not breastfeed
Breastfeeding during night Sasaki et al. (2009) [23] Longitudinal 908 1. Only breastfeeding N/A N/A 2.62(1.85,3.73) Not breastfeeding during night =1 (reference) (p < 0.01)
     2. Breastmilk and infant formula     
     3. Only infant formula     
  1. Note: N/A = Not Applicable, wks = weeks postpartum, m = months postpartum.