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Milk intake and risk of mortality and fractures in women and men: cohort studies

BMJ 2014; 349 doi: https://doi.org/10.1136/bmj.g6015 (Published 28 October 2014) Cite this as: BMJ 2014;349:g6015
  1. Karl Michaëlsson, professor1,
  2. Alicja Wolk, professor2,
  3. Sophie Langenskiöld, senior lecturer3,
  4. Samar Basu, professor3,
  5. Eva Warensjö Lemming, researcher14,
  6. Håkan Melhus, professor5,
  7. Liisa Byberg, associate professor1
  1. 1Department of Surgical Sciences, Uppsala University, SE-751 85 Uppsala, Sweden
  2. 2Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
  3. 3Department of Public Health and Caring Sciences, Uppsala University, Uppsala, Sweden
  4. 4Swedish National Food Agency, Uppsala, Sweden
  5. 5Department of Medical Sciences, Uppsala University, Uppsala, Sweden
  1. Correspondence to: K Michaëlsson karl.michaelsson{at}surgsci.uu.se
  • Accepted 22 September 2014

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.

Footnotes

  • Contributors: KM and LB designed the study and drafted the manuscript. KM and LB analysed the data. LB, HM, SL, SB, EWL, and AW contributed to the interpretation of the data and revision of the manuscript. KM had primary responsibility for final content and acts as guarantor. All authors read and approved the final manuscript. The funders of the study had no role in the study design, data collection, data analysis, data interpretation, writing of the report, or the decision to submit the article for publication.

  • Funding: This study was supported by grants from the Swedish Research Council. EWL is employed by the Swedish National Food Agency. The views in this article do not necessarily represent those of the agency.

  • 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.

  • Ethical approval: The Swedish Mammography Cohort, the clinical subcohort of the Swedish Mammography Cohort, and the Cohort of Swedish Men were approved by the regional research ethics board at Karolinska Insitutet. The Uppsala Longitudinal Study of Adult Men was approved by the regional research ethics board at Uppsala University. All participants gave informed consent.

  • Data sharing: Summary data from the Uppsala Longitudinal Study of Adult Men are available at http://www.pubcare.uu.se/ULSAM.

  • Transparency: The lead author (KM) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

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