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Am J Epidemiol. 2019 Apr 1;188(4):637-645. doi: 10.1093/aje/kwy285.

The Association of a Breast Cancer Diagnosis With Serum 25-Hydroxyvitamin D Concentration Over Time.

Author information

1
Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina.
2
Biostatistics and Computational Biology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina.
3
Westat, Inc., Durham, North Carolina.

Abstract

Prospective and retrospective studies of vitamin D levels and breast cancer have produced discrepant results. This may be due to variations in serum 25-hydroxyvitamin D (25(OH)D) concentrations over time, including systematic changes after breast cancer diagnosis. We measured total serum 25(OH)D levels in participants from the Sister Study, a US cohort study of sisters of breast cancer patients, who provided samples at baseline (2003-2009) and 4-10 years later (2013-2015). This included 827 women with an intervening breast cancer and 771 women without one. Although 25(OH)D levels were modestly correlated over time (R = 0.42), 25(OH)D concentrations increased in both groups, with larger increases among cases (averaging 31.6 ng/mL at baseline and 43.5 ng/mL at follow-up) than among controls (32.3 ng/mL at baseline, 40.4 ng/mL at follow-up). Consequently, the estimated association between 25(OH)D and breast cancer depended on whether baseline measurements (per 10-ng/mL increase, odds ratio = 0.87, 95% confidence interval: 0.78, 0.98) or measurements from the second blood draw (per 10-ng/mL increase, odds ratio = 1.17, 95% confidence interval: 1.08, 1.26) were used. Concentrations were related to regular use (≥4 times/week) of vitamin D supplements, which became more common over time; increases in regular use were greater in cases (from 56% to 84%) than in controls (from 56% to 77%). Our results do not explain previously observed differences between retrospective and prospective studies, but they do demonstrate how reverse causation and temporal trends in exposure can distort inference.

KEYWORDS:

25-hydroxyvitamin D; breast cancer; reliability; reverse causation bias; vitamin D

PMID:
30608512
PMCID:
PMC6454838
[Available on 2020-04-01]
DOI:
10.1093/aje/kwy285

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