Abstract

Background Mendelian randomization (MR) studies suggest a causal effect of iron (Fe) status on cardiovascular disease (CVD) risk, but it is unknown if these associations are confounded by pleiotropic effects of the instrumental variables (IV) on CVD risk factors. We aimed to investigate the effect of Fe status on CVD risk controlling for CVD risk factors.

Methods Fe biomarker IVs (total Fe binding capacity (TIBC, n=208,422), transferrin saturation (TSAT, n=198,516), serum Fe (SI, n=236,612), ferritin (n=257,953)) were selected from a European GWAS meta-analysis. We performed two-sample univariate (UV) MR of each Fe trait on CVD outcomes (all-cause ischemic stroke (IS), cardioembolic IS (CES), large artery IS (LAS), small vessel IS (SVS), and coronary heart disease (CHD)) from MEGASTROKE (n=440,328) and CARDIoGRAMplusC4D (n=183,305). We then implemented multivariate (MV) MR conditioning on six CVD risk factors from independent European samples to evaluate their potential confounding and/or mediating effects on the observed Fe-CVD associations.

Results With UVMR analyses, we found higher genetically predicted Fe status to be associated with a greater risk of CES (TSAT: OR 1.17 [95%CI 1.03, 1.33], SI: OR 1.21 [ 95%CI 1.02, 1.44]; TIBC: OR 0.81 [95%CI 0.69, 0.94]). The detrimental effects of Fe status on CES risk remained unaffected when adjusting for CVD risk factors (all P<0.05). Additionally, we found diastolic blood pressure (DBP) to mediate between 7.1-8.8% of the total effect of Fe status on CES incidence. While UVMR initially suggested a protective effect of Fe status on LAS and CHD, MVMR analyses factoring CVD risk factors revealed a complete annulment of this perceived protective effect (all P>0.05).

Discussion Higher Fe status was associated with a greater risk of CES independent of CVD risk factors, and this effect was partly mediated by DBP. These findings support a role of Fe status as a modifiable risk factor for CES.

Competing Interest Statement

The authors have declared no competing interest.

Clinical Trial

NA

Funding Statement

This work was supported by the American Heart Association (23PRE1025636) and the NIH National Institute of Diabetes and Digestive and Kidney Diseases (R01DK122216). The funding sources were not involved in the preparation of the manuscript.

Author Declarations

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

All analyses were based on publicly available summary statistics, therefore, no ethical approval from an institutional review board was required. No patients were involved in the design of the study.

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Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

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Data and Code Availability

The GWAS summary-level data are publicly available for all exposures and outcomes evaluated. The exposure summary-statistic can be found directly from the original GWAS publication (27). Data on coronary artery disease have been contributed by CARDIoGRAMplusC4D investigators. The UK Biobank, CARDIOGRAMplusC4D consortium, MEGASTROKE, and IL-6 GWAS summary-level data are available in IEU OpenGWAS (https://gwas.mrcieu.ac.uk/). The MR analysis code may be obtained from the corresponding author upon reasonable request.

AbbreviationsAFatrial fibrillationApo-Aapolipoprotein-AApo-Bapolipoprotein-BBMIbody mass indexCARDIoGRAMplusC4DCoronary ARtery DIsease Genome wide Replication and Meta-analysis plus The Coronary Artery Disease GeneticsCEScardioembolic ischemic strokeCHDcoronary heart diseaseCVDcardiovascular diseaseDBDSDanish Blood Donor StudyDBPdiastolic blood pressure;FeironHDLhigh density lipoprotein cholesterolHUNTTrøndelag Health StudyIL-6interleukin-6ISall-cause ischemic strokeIVinstrumental variableIVWinverse variance weightedLASlarge artery atherosclerosis ischemic strokeLDLlow density lipoprotein cholesterolMGIMichigan Genomics InitiativeMRMendelian randomizationMR-PRESSOMendelian randomization pleiotropy residual sum and outlier testMVMRmultivariate Mendelian randomizationNTBInon-transferrin bound ironSBPsystolic blood pressureSVSsmall vessel ischemic strokeTCtotal cholesterolTGtriglyceridesTIBCtotal iron binding capacityTSATtransferrin saturationUKBBUK Biobank.