Dietary calcium intake and risk of fracture and osteoporosis: prospective longitudinal cohort studyBMJ 2011; 342 doi: https://doi.org/10.1136/bmj.d1473 (Published 24 May 2011) Cite this as: BMJ 2011;342:d1473
- Eva Warensjö, researcher14,
- Liisa Byberg, researcher14,
- Håkan Melhus, professor34,
- Rolf Gedeborg, associate professor24,
- Hans Mallmin, professor1,
- Alicja Wolk, professor5,
- Karl Michaëlsson, professor14
- 1Department of Surgical Sciences, Section of Orthopaedics, Uppsala University, Uppsala, Sweden
- 2Department of Surgical Sciences, Anaesthesiology and Intensive Care, Uppsala University
- 3Department of Medical Sciences, Clinical Pharmacology, Uppsala University
- 4Uppsala Clinical Research Centre, UCR, Uppsala University
- 5Division of Nutritional Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
- Correspondence to: E Warensjö
- Accepted 28 February 2011
Objective To investigate associations between long term dietary intake of calcium and risk of fracture of any type, hip fractures, and osteoporosis.
Design A longitudinal and prospective cohort study, based on the Swedish Mammography Cohort, including a subcohort, the Swedish Mammography Cohort Clinical.
Setting A population based cohort in Sweden established in 1987.
Participants 61 433 women (born between 1914 and 1948) were followed up for 19 years. 5022 of these women participated in the subcohort.
Main outcome measures Primary outcome measures were incident fractures of any type and hip fractures, which were identified from registry data. Secondary outcome was osteoporosis diagnosed by dual energy x ray absorptiometry in the subcohort. Diet was assessed by repeated food frequency questionnaires.
Results During follow-up, 14 738 women (24%) experienced a first fracture of any type and among them 3871 (6%) a first hip fracture. Of the 5022 women in the subcohort, 1012 (20%) were measured as osteoporotic. The risk patterns with dietary calcium were non-linear. The crude rate of a first fracture of any type was 17.2/1000 person years at risk in the lowest quintile of calcium intake, and 14.0/1000 person years at risk in the third quintile, corresponding to a multivariable adjusted hazard ratio of 1.18 (95% confidence interval 1.12 to 1.25). The hazard ratio for a first hip fracture was 1.29 (1.17 to 1.43) and the odds ratio for osteoporosis was 1.47 (1.09 to 2.00). With a low vitamin D intake, the rate of fracture in the first calcium quintile was more pronounced. The highest quintile of calcium intake did not further reduce the risk of fractures of any type, or of osteoporosis, but was associated with a higher rate of hip fracture, hazard ratio 1.19 (1.06 to 1.32).
Conclusion Gradual increases in dietary calcium intake above the first quintile in our female population were not associated with further reductions in fracture risk or osteoporosis.
Contributors: KM and EW designed the study, analysed and interpreted the data, and drafted the manuscript. AW contributed to the study design, analysis and interpretation of the data, and writing of the manuscript. LB, HMa, HM, and RG interpreted the data and made significant contributions to drafts of the manuscript. All authors had full access to all data (including statistical reports and tables) in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. EW and KM are guarantors.
Funding: Supported by the Swedish Research Council, grant numbers 2008-2202 and 2009-6281. The funding source was not involved in the design, conduct or interpretation of the study, or in the writing of the submitted work.
Competing interests: All authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) 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 study was approved by the regional ethics committees at Uppsala University, Uppsala, and Karolinska Institutet, Stockholm, Sweden, and all participants gave their informed consent.
Data sharing: No additional data available.
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