Breast-feeding and cancer: the Boyd Orr cohort and a systematic review with meta-analysis.
BACKGROUND
Having been breast-fed has been suggested to influence cancer risk in adulthood. We investigated associations between breast-feeding during infancy and adult cancer incidence and mortality in a cohort study and meta-analyses of published studies.


METHODS
The Boyd Orr cohort consisted of 4999 subjects who were originally surveyed in 1937-39, when they were 0-19 years of age. Cancer outcomes from 1948 through 2003 were available for 4379 (88%) subjects, and 3844 had complete data on all covariates. Associations of breast-feeding with cancer were investigated using proportional hazards models. We also identified 14 studies on infant feeding and cancer published from 1966 through July 2005, of which 10 could be combined with the Boyd Orr cohort results in a meta-analysis of breast cancer using random-effect models.


RESULTS
In the Boyd Orr cohort, ever having been breast-fed, compared with never having been breast-fed, was not associated with the incidence of all cancers (hazard ratio [HR] = 1.07, 95% confidence interval [CI] = 0.89 to 1.28) or of any individual cancer type examined (prostate HR = 1.43, 95% CI = 0.58 to 3.52; breast HR = 1.62, 95% CI = 0.89 to 2.94; colorectal HR = 0.86, 95% CI = 0.45 to 1.63; gastric HR = 1.22, 95% CI = 0.47 to 3.15). In the meta-analysis, there was also no association between breast-feeding and breast cancer (regardless of menopausal status) (relative risk [RR] = 0.94, 95% CI = 0.85 to 1.04). However, breast-fed women had a reduced risk of premenopausal breast cancer (RR = 0.88, 95% CI = 0.79 to 0.98) but not of postmenopausal breast cancer (RR = 1.00, 95% CI = 0.86 to 1.16).


CONCLUSIONS
Ever having been breast-fed was not associated with overall breast cancer risk, although the meta-analysis revealed a reduced risk of premenopausal breast cancer in women who had been breast-fed.
Martin
Richard M
RM
Department of Social Medicine, University of Bristol, Canynge Hall, Bristol BS8 2PR, United Kingdom. richard.martin@bristol.ac.uk
Middleton
Nicos
N
Gunnell
David
D
Owen
Christopher G
CG
Smith
George Davey
GD
D000328:Adult; D000368:Aged; D001942:Breast Feeding; D001943:Breast Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D016001:Confidence Intervals; D015986:Confounding Factors, Epidemiologic; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology* / Q000517:prevention & control*; D016017:Odds Ratio; D016016:Proportional Hazards Models; D011471:Prostatic Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D018570:Risk Assessment; D013274:Stomach Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D013736:Testicular Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D006113:United Kingdom / Q000453:epidemiology