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Research Interests

The O’Brien Laboratory is working to understand the nutritional, endocrine, and genomic factors that interact to regulate calcium, vitamin D, and iron homeostasis.

Ongoing Research Projects

Heme and Non-Heme Iron Intakes, Gut Microbiota and Influence on Host Iron Absorption (FeMicrobiome)

Study Principal Investigator: Kimberly O'Brien, PhD  

Specific Aims: The FeMicrobiome study will study the impact of a plant-based or mixed diet (animal and plant intake) on iron absorption and the gut microbiome. Some bacteria in the gut can produce substances that decrease the hosts ability to absorb iron when dietary iron intake is low. Other gut bacteria cannot make heme and must rely on host intake of heme iron. We will evaluate interactions between diet, the gut microbiome and iron absoroption using stable iron isotopes in healthy young adult men and women.  

Study Population: 120 Healthy adult men and women consuming a plant-based (n=60) or animal product-containing diet (n=60).
Funded by: The US Department of Agriculture (AFRI/NIFA USDA)


Study Co Principal Investigators: Xingen Lei and Walter Bottje

Specific Aims: This study involves a large transdisciplinary team from the University of Arkansas, Cornell University and eight other institutions to innovate and integrate research, teaching and extension to empower US broiler production for growth, profitability and sustainability. Vitamin D and omega-3 fatty acids are nutrients of concern in the US diet. Animal products are known to contain 25(OH)D and this form of vitamin D is thought to be significantly more bioavailable than vitamin D. Sources of omega-3 fatty acids are limited in the US diet. Our role in this project will be to help develop poultry that is bioenhanced to contain omega-3 fatty acids and 25-hydroxyvitamin D.  Potential health benefits of these bioenhanced forms of chicken will be tested in human studies carried out in our Human Metabolic Research Unit.

Funded by: USDA AFRI-NRI 

Impact of Obesity, DBP Genotype and Pregnancy on Vitamin D Kinetics

Study Co Principal Investigators: Kimberly O’Brien and Eva Pressman

Specific Aims: This study will utilize deuterated cholecalciferol to evaluate vitamin D3 absorption, conversion into 25(OH)D3 and half-life of 25(OH)D3 in pregnant women and non-pregnant women and during each trimester of pregnancy in women who do or do not have obesity. The impact of stage of gestation, obesity, and vitamin D binding genotype of vitamin D kinetics will be evaluated. Fat biopsies will be obtained to evaluate vitamin D concentrations in adipose tissue as a function of DBP genotype, adiposity and stage of gestation. Key vitamin D metabolic proteins in the placenta will be evaluated in relation to maternal and neonatal D status. 

Funded by: NICHD (scored 3rd percentile, funding pending)

Completed Studies 

Ethnic Differences in Iron Absorption (FeGenes) 

Study Co-Principal Investigators: Kimberly O'Brien, PhD and Zhenglong Gu, PhD
Specific Aims: The FeGenes study stands for iron(Fe) Genes in East Asians and Northern Europeans study. This study will take a multidisciplinary approach to study genetic variations in genes that control Fe metabolism and utilization in order to shed light on the genetic basis of population differences in Fe metabolism and disease susceptibility and to inform population-specific dietary Fe intake recommendations with the long-term goal of minimizing the risk of chronic diseases. More specifically, we will employ in vivo approach using stable iron isotope method to measure iron absorption directly and characterize the genetic makeup by genotyping array.
Study Population: 250 East Asians and 250 Northern Europeans
Funded by: NIH-NIDDK and The Office of Dietary Supplements (ODS)

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Characterization of Iron Regulatory Hormone Erythroferrone During Pregnancy 

Study Co-Principal Investigators: Kimberly O'Brien, PhD and Elizabeta Nemeth, PhD
Specific Aims: Maternal iron deficiency increases the risk of adverse birth outcomes and inadequate neonatal iron endowment, which may lead to irreversible adverse effects on fetal brain development. During pregnancy, adaptations to iron homeostasis occur due to increased maternal, neonatal and placental iron demands, Maternal iron absorption and release from stores is regulated in response to iron demands via regulatory hormones erythropoietin, hepcidin and erythroferrone. While data on erythropoietin and hepcidin during pregnancy exist, no data on erythroferrone in human pregnancies exist due to previous lack of validated human assay. Therefore, the study aims to characterize erythroferrone during pregnancy and to assess its utility as an indicator of iron status.
Funded by: NIH-NICHD

Determinants of Neonatal Iron Homeostasis in Women Carrying Multiples

Study PI: Kimberly O'Brien;  Co-Principal Investigators: Eva Pressman, MD; Ronnie Guillet MD, PhD; Philip Katzman, MD; and Elizabeth Cooper, CNM, RD
Specific Aims:
1. To learn more about iron status in women having twins and triplets and to see how maternal iron status influences the amount of iron that is present in babies at birth
2. Maternal weight gain, hematological measures, Fe status indicators and serum hepcidin were longitudinally assessed across pregnancy in women carrying multiples during routine blood testing for alpha-feroprotein.
3. Cord blood were obtained from each neonate at delivery.
4. Inflammatory markers (CRP IL-6) were measured in all maternal and cord blood samples and related to outcomes.
Study Population: 140 pregnant adolescents (age 11-18 y) and their newborn infants
Funded by: Gerber Foundation


Lab Equipment


The O'Brien Laboratory Triton was installed in the Human Metabolic Research Unit (HMRU) in September 2005 to measure stable mineral isotopes in biological samples. The Triton achieves very precise and accurate isotopic ratios for positive and negative ions and gives the ultimate precision for isotope ratio measurements on solid samples. It uses a proven thermal ionization source and has a unique variable multi-collector platform which can be configured with Faraday detectors and/or miniaturized ion counting detectors for smallest sample sizes. (Thermo Fischer Scientific, Inc., 2008)

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