Abstract
BackgroundObservational studies and meta-analyses relating milk consumption by adults to all-cause mortality, coronary heart disease and stroke have obtained contradictory results. Some studies found a protective effect of milk consumption, whilst other found an increased risk.MethodsWe performed a systematic literature search until June 2015 on prospective studies that looked at milk consumption, all-cause mortality, coronary heart disease and stroke. Random-effect meta-analyses were performed with dose-response.ResultsTwenty-one studies involving 19 cohorts were included in this meta-analysis, 11 on all-cause mortality, 9 on coronary heart disease, and 10 on stroke. Milk intake ranged from 0 to 850 mL/d. The summary relative risk (SRR) for 200 mL/d milk consumption was 1.01 (95% CI: 0.96–1.06) for all-cause mortality, 1.01 (95% CI: 0.98–1.05) for fatal and non fatal coronary heart disease, and 0.91 (95% CI: 0.82–1.02) for fatal and non fatal stroke. Stratified analyses by age, Body Mass Index, total energy intake and physical acitivity did not alter the SRR estimates. The possibility of publication bias was found for all cause mortality and for stroke, indicating a gap in data that could have suggested a higher risk of these conditions with increased milk consumption.ConclusionsWe found no evidence for a decreased or increased risk of all-cause mortality, coronary heart disease, and stroke associated with adult milk consumption. However, the possibility cannot be dismissed that risks associated with milk consumption could be underestimated because of publication bias.Electronic supplementary materialThe online version of this article (doi:10.1186/s12889-016-3889-9) contains supplementary material, which is available to authorized users.
Highlights
Observational studies and meta-analyses relating milk consumption by adults to all-cause mortality, coronary heart disease and stroke have obtained contradictory results
[5] We excluded five studies selected by Soedamah-Muthu et al [5] because of absence of data specific to milk consumption [36, 37] or data were about dairy products and not about milk alone [11, 38, 39]
Results of the Rotterdam study on milk consumption and stroke or coronary heart disease were published by Praagman et al [33], which we included in this meta-analysis
Summary
We included 21 studies in our meta-analysis, involving 19 cohorts (Fig. 1 and Additional file 1: Table S1) [6, 9, 10, 12,13,14,15,16,17,18,19,20,21, 28,29,30,31,32,33,34,35]. Despite the relatively small number of published data, the Macaskill test and to some extent, the Egger test suggested the presence of publication bias for all cause mortality and fatal and non-fatal stroke (Additional file 2: Table S2). The Additional file 2: Figure S1 shows an assymetry in the spread of relative risks in the plot, with a gap in the right lower part of the plot These gaps suggest that a number of smaller size studies that found increased risks of all cause mortality were not published. The main results of the two studies that could not be integrated in the meta-analysis were a relative risk of coronary heart disease of 0.99 (95% CI: 0.71–1.38) in men and of 1.01 (95% CI: 0.68–1.49) in women associated with sometimes/often whole milk consumption relative to never/rare milk consumption [42]. (p < 0.05) in men and of 1.11 (p > 0.05) in women when comparing two glasses of milk a day versus none
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