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

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