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Observational Study
. 2014 Oct 28;349:g6015.
doi: 10.1136/bmj.g6015.

Milk Intake and Risk of Mortality and Fractures in Women and Men: Cohort Studies

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Free PMC article
Observational Study

Milk Intake and Risk of Mortality and Fractures in Women and Men: Cohort Studies

Karl Michaëlsson et al. BMJ. .
Free PMC article

Abstract

Objective: To examine whether high milk consumption is associated with mortality and fractures in women and men.

Design: Cohort studies.

Setting: Three counties in central Sweden.

Participants: Two large Swedish cohorts, one with 61,433 women (39-74 years at baseline 1987-90) and one with 45,339 men (45-79 years at baseline 1997), were administered food frequency questionnaires. The women responded to a second food frequency questionnaire in 1997.

Main outcome measure: Multivariable survival models were applied to determine the association between milk consumption and time to mortality or fracture.

Results: During a mean follow-up of 20.1 years, 15,541 women died and 17,252 had a fracture, of whom 4259 had a hip fracture. In the male cohort with a mean follow-up of 11.2 years, 10,112 men died and 5066 had a fracture, with 1166 hip fracture cases. In women the adjusted mortality hazard ratio for three or more glasses of milk a day compared with less than one glass a day was 1.93 (95% confidence interval 1.80 to 2.06). For every glass of milk, the adjusted hazard ratio of all cause mortality was 1.15 (1.13 to 1.17) in women and 1.03 (1.01 to 1.04) in men. For every glass of milk in women no reduction was observed in fracture risk with higher milk consumption for any fracture (1.02, 1.00 to 1.04) or for hip fracture (1.09, 1.05 to 1.13). The corresponding adjusted hazard ratios in men were 1.01 (0.99 to 1.03) and 1.03 (0.99 to 1.07). In subsamples of two additional cohorts, one in males and one in females, a positive association was seen between milk intake and both urine 8-iso-PGF2α (a biomarker of oxidative stress) and serum interleukin 6 (a main inflammatory biomarker).

Conclusions: High milk intake was associated with higher mortality in one cohort of women and in another cohort of men, and with higher fracture incidence in women. Given the observational study designs with the inherent possibility of residual confounding and reverse causation phenomena, a cautious interpretation of the results is recommended.

Conflict of interest statement

Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

Figures

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Fig 1 Flow chart of study samples
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Fig 2 Sex specific multivariable adjusted spline curves of relation between milk intake with time to death from all causes, hip fracture, and any type of fracture. Covariates were age, total energy intake, body mass index, height, educational level, living alone, calcium supplementation, vitamin D supplementation, ever use of cortisone, healthy dietary pattern, physical activity, smoking status, and Charlson’s comorbidity index. The spike plot represents the distribution of milk intake. One glass of milk corresponds to 200 g
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Fig 3 Sex specific multivariable adjusted spline curves of relation between milk intake with time to death from all cancer and cardiovascular disease (CVD). Covariates were age, total energy intake, body mass index, height, educational level, living alone, calcium supplementation, vitamin D supplementation, ever use of cortisone, healthy dietary pattern, physical activity, smoking status, and Charlson’s comorbidity index. The spike plot represents the distribution of milk intake. One glass of milk corresponds to 200 g
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Fig 4 Adjusted predictions of urine log(8-iso-PGF2α), a marker of oxidative stress, in 892 women (based on cross sectional data, mean age 70 years) and 700 men, and serum log(interleukin 6), a marker of inflammation, in 633 men after cubic-spline regression with milk consumption. Data for men are based on milk consumption assessed at age 71 years and measurement of inflammatory markers at age 77 years. Covariates were age, body mass index, energy intake, education, smoking status, and physical activity. One glass of milk corresponds to 200 g

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