Background
Methods
Study design
Sample collection
Biochemical analyses of human milk
Carbohydrate content
Protein content
Creamatocrit, lipid content, and energy conversion
Immunoglobulin a (IgA)
Total antioxidant capacity
Statistical analysis
Results
Breastfeeding 1–6 months (n = 43) | Breastfeeding 6–12 months (n = 47) | Breastfeeding 12–18 months (n = 50) | Breastfeeding 18–24 months (n = 44) | p-value | |
---|---|---|---|---|---|
Maternal age, years (mean ± SD; median, P25th–75th) 1 | 32.6 ± 3.6, 32, 29–35 | 30.9 ± 4.6, 31, 28–35 | 32.2 ± 4.8, 32, 33–36 | 32.0 ± 4.5, 32, 29–37 | 0.28 |
Maternal BMI, kg/m2 (mean ± SD; median, P25th–75th) 2 | 23.2 ± 4.5, 22.5, 19.7–24.8 | 22.6 ± 4.8, 21.3, 19–25.1 | 22.3 ± 4.1, 21.6, 20.2–23.8 | 22.3 ± 3.3, 21.7, 19.8–25.1 | 0.78 |
Educational level (n, %)3 | |||||
Primary school | 9 (20.9) | 7 (14.9) | 16 (32.0) | 12 (27.3) | 0.13 |
Secondary school/certificate | 0 (0) | 3 (6.4) | 4 (8.0) | 4 (9.1) | |
Graduate degree | 34 (79.1) | 37 (78.7) | 30 (60.0) | 28 (63.6) | |
First ANC visit, months (mean ± SD; median, P25th–75th) 2 | 2.0 ± 1.3, 2, 1–2 | 2.3 ± 1.6, 2, 1–3 | 2.3 ± 1.3, 2, 1–3 | 2.1 ± 1.2, 2, 1–3 | 0.78 |
Gestational age, days (mean ± SD; median, P25th–75th) 2 | 270.6 ± 6.4, 272, 266–273 | 271.3 ± 8.1, 272, 266–278 | 271.5 ± 6.4, 273, 266–275 | 272.3 ± 8.3, 273, 266–280 | 0.84 |
Birth order 3 (n, %) | |||||
First born | 27 (62.8) | 31 (66.0) | 33 (66.0) | 25 (56.8) | 0.71 |
Second born | 15 (34.9) | 15 (31.9) | 13 (26.0) | 16 (36.4) | |
Third-fifth born | 1 (2.3) | 1 (2.1) | 4 (8.0) | 3 (6.8) | |
Parental status, couple (n, %) 3 | 42 (97.7) | 47 (100) | 48 (96.0) | 44 (100) | 0.46 |
Breastfeeding frequency, times per day (mean ± SD; median, P25th–75th) 2 | 6.4 ± 5.6, 6, 1–10 | 6.0 ± 4.8, 5, 2–9 | 5.7 ± 3.8, 6, 3–8 | 6.1 ± 3.9, 5, 3.2–8 | 0.98 |
Associations between human milk composition and the duration of lactation
Macronutrients
Breastfeeding Duration | 1–6 months (n = 43) a | 6–12 months (n = 47) b | 12–18 months (n = 50) c | 18–24 months (n = 44) d | Mean rank or Mean diff. (SE) | p-value | ||||
---|---|---|---|---|---|---|---|---|---|---|
Mean ± SD | Median, P25th–75th | Mean ± SD | Median, P25th–75th | Mean ± SD | Median, P25th–75th | Mean ± SD | Median, P25th–75th | |||
Protein (g/dL) | 2.56 ± 0.62 | 2.53, 2.21–2.92 | 2.39 ± 0.52 | 2.23, 2.05–2.69 | 2.40 ± 0.75 | 2.36, 1.87–2.61 | 2.84 ± 0.90 | 2.66, 2.29–3.13 | 50.49, 40.94 ab 52.22, 42.51 ac 40.23, 47.68 ad 50.09, 47.98 bc 37.34, 55.25 bd 38.87, 57.31 cd | < 0.001 1 0.08 2 0.08 2 0.17 2 0.71 2 0.001 2 < 0.0012 |
Fat (g/dL) | 3.67 ± 1.30 | 3.79, 2.92–4.33 | 3.96 ± 1.36 | 3.53, 3.17–4.83 | 3.90 ± 1.32 | 3.85, 3.17–4.68 | 4.64 ± 1.61 | 4.61, 3.8–5.13 | 41.26, 49.38 ab 42.78, 50.63 ac 34.69, 53.10 ad 49.20, 48.81 bc 40.88, 51.47 bd 41.67, 54.13 cd | < 0.0011 0.14 2 0.16 2 < 0.001 2 0.94 2 0.06 2 0.03 2 |
Energy (kcal/dL) | 84.86 ± 12.93 | 86.09, 77.42–91.55 | 87.77 ± 13.61 | 83.54, 79.94–96.55 | 87.91 ± 13.23 | 86.70, 79.94–95.01 | 94.64 ± 16.13 | 94.28, 86.24–99.48 | 41.26, 49.38 ab 42.77, 50.64 ac 34.67, 53.11 ad 49.20, 48.81 bc 40.88, 51.47 bd 41.67, 54.13 cd | < 0.0011 0.14 2 0.16 2 0.001 2 0.94 2 0.06 2 0.03 2 |
Carbohydrate (g/dL) | 9.62 ± 1.04 | 9.43, 8.97–10.12 | 9.34 ± 0.59 | 9.27, 8.97–9.71 | 9.31 ± 0.84 | 9.35, 8.95–9.74 | 9.39 ± 0.81 | 9.41, 8.96–9.73 | 48.90, 42.39 ab 49.73, 44.65 ac 46.53, 41.52 ad 48.12, 49.83 bc 44.83, 47.25 bd 47.48, 47.52 cd | 0.65 1 0.24 2 0.36 2 0.35 2 0.76 2 0.66 2 0.99 2 |
IgA (mg/dL) | 110.82 ± 14.06 | 111.48, 103–117.63 | 129.59 ± 16.67 | 130.33, 115.03–140.5 | 124.29 ± 10.80 | 125.07, 116.35–131.37 | 127.16 ± 14.59 | 126.06, 115.73–139.57 | − 18.77 (3.18) ab − 13.47 (3.14) ac − 16.34 (3.23) ad 5.31 (3.06) bc 2.43 (3.16) bd − 2.87 (3.12) cd | < 0.0013 < 0.001 4 < 0.001 4 < 0.0014 0.08 4 0.44 4 0.36 4 |
TAC | 1.61 ± 0.94 | 1.62, 1.2–2.04 | 1.61 ± 0.67 | 1.64, 1.89–2.05 | 1.84 ± 0.85 | 1.84, 1.38–2.38 | 1.60 ± 0.97 | 1.27, 0.69–2.09 | 0.03 (0.18) ab − 0.23 (0.18) ac 0.21 (0.18) ad − 0.23 (0.18) bc 0.18 (0.18) bd 0.44 (0.18) cd | 0.09 3 0.85 4 0.19 4 0.25 4 0.19 4 0.33 4 0.01 4 |
Immunoglobulin a
Total antioxidant capacity
Factors affecting human milk composition
Protein (g/dL) | Fat (g/dL) | Energy (kcal/dL) | Carbohydrate (g/dL) | IgA (mg/dL) | TAC (mM) | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
B (SE) | 95% CI | B (SE) | 95% CI | B (SE) | 95% CI | B (SE) | 95% CI | B (SE) | 95% CI | B (SE) | 95% CI | |
Months of lactation | 0.09 (0.05) | − 0.01, 0.19 (p = 0.06) | 0.31 (0.09) | 0.13, 0.49 (p = 0.001) | 3.11 (0.92) | 1.30, 4.92 (p = 0.001) | − 0.22 (0.01) | − 0.22, − 0.01 (p = 0.04) | 4.17 (1.08) | 2.03, 6.31 (p < 0.001) | − 0.04 (0.06) | − 0.15, 0.08 (p = 0.54) |
Maternal age | − 0.01 (0.01) | − 0.03, 0.02 (p = 0.62) | − 0.03 (0.02) | − 0.08, 0.01 (p = 0.18) | − 0.32 (0.23) | − 0.78, 0.14 (p = 0.17) | 0.02 (0.01) | − 0.004, 0.05 (p = 0.09) | − 0.40 (0.28) | − 0.95, 0.14 (p = 0.15) | 0.03 (0.02) | − 0.01, − 0.05 (p = 0.10) |
Maternal BMI | 0.02 (0.01) | − 0.003, 0.048 (p = 0.09) | 0.09 (0.02) | 0.04, 0.14 (p < 0.001) | 0.88 (0.24) | 0.40, 1.36 (p < 0.001) | − 0.04 (0.01) | − 0.06, − 0.01 (p = 0.02) | −0.40 (0.29) | − 0.96, 0.14 (p = 0.17) | −0.02 (0.02) | − 0.05, 0.02 (p = 0.35) |
Birth order | −0.02 (0.09) | − 0.19, 0.16 (p = 0.85) | 0.19 (0.16) | − 0.13, 0.52 (p = 0.25) | 1.92 (1.64) | − 1.33, 5.16 (p = 0.25) | − 0.22 (0.16) | −0.22, 0.27 (p = 0.77) | − 0.15 (1.94) | −3.98, 3.69 (p = 0.94) | −0.003 (0.11) | − 0.21, 0.20 (p = 0.98) |
Breastfeeding frequency | −0.01 (0.01) | − 0.04, 0.01 (p = 0.27) | −0.001 (0.023) | − 0.05, 0.04 (p = 0.97) | −0.01 (0.23) | − 0.46, 0.44 (p = 0.97) | −0.04 (0.02) | − 0.04, 0.01 (p = 0.39) | −0.20 (0.27) | − 0.73, 0.33 (p = 0.45) | 0.02 (0.02) | − 0.004, 0.05 (p = 0.10) |