Table 3. Results of studies assessing an association between insufficient milk supply and premenopausal breast cancer; stratified by reference group (a. studies comparing women who experienced insufficient milk to parous women who breastfed successfully, b. breastfed unsuccessfully for other reasons, c. never breastfed).
| Study | N cases / N controls | Age | Definition of Insufficient Milk Supply | Crude OR (95% CI) | Adjusted OR (95% CI); Adjusted for… | Notes About Comparison Group |
| a. | ||||||
| Shema 2007 | 68/128 | 30–75 | Unsuccessful attempt at breastfeeding or quitting before 1 month because of insufficient milk | 16.3 (3.5–150) | Breastfed for 1–12 months and 12+ months combined | |
| Freudenheim 1997 | 81/110 | 40–85 | Reported as the reason for cessation of breastfeeding within 1.5 months of any birth | 1.2 (0.4–3.0) | 0.9 (0.3–2.4); Age, parity, education, FHBC, history of BBD*, age at menarche, at first birth | Lactated and did not experience insufficient milk after any birth |
| Newcomb 1994 | 556/1150 | <75 | Reported experience of insufficient milk within the first 3 months of first or second birth | 1.0 (0.8–1.3) | 1.0 (0.8–1.3); Age, parity, age at menarche, fist birth, first lactation, history of BBD, FHBC, BMI | It is unclear how long the comparison group breastfed for |
| Yang 1993 | 178/211 | <75 | Breastfed unsuccessfully (<1 month) and reported the reason as insufficient milk | 3.2 (1.4–8.0) | 3.1 (1.4–6.7); Age, parity | Breastfed for ≥2 months |
| Byers 1985 | 66/288 | 40–84 | Reported as the reason for cessation of breastfeeding after the first birth | 2.2 (1.2–3.9) | 2.10; Age | Successfully lactated for any length of time and then stopped for reasons other than insufficient milk supply |
| b. | ||||||
| Brinton 1995 | 96/73 | <45 | Reported as the reason for breastfeeding for <2 weeks | 1.5 (0.7–3.6) | Reported breastfeeding <2 weeks for reasons other than insufficient milk | |
| Yang 1993 | 41/17 | <75 | Breastfed unsuccessfully (<1 month) and reported the reason as insufficient milk | 1.0 (0.3–3.7) | Breastfed unsuccessfully (<1 month) and reported any other reason | |
| c. | ||||||
| Shema 2007 | 50/34 | 30–75 | Reported unsuccessful breastfeeding attempt or reported quitting breastfeeding before 1 month because of insufficient milk | 6.2 (1.3–59.5) | Lifetime duration of breastfeeding = 0 months | |
| Yang 1993 | 96/76 | <75 | Breastfed unsuccessfully (<1 month) and reported the reason as insufficient milk | 2.2 (0.9–5.8) | Never lactated | |
*
FHBC = family history of breast cancer BMI = body mass index (kg/m2) BBD = benign breast disease.