Andrew J. Clifford, Ph.D.

Andres Clifford

Position Title
(In Memoriam) Distinguished Professor Emeritus

  • B.S., University College, Dublin, Ireland
  • M.S., University College, Dublin, Ireland
  • Ph.D., Oklahoma State University, Stillwater, OK
Research Interests

Dr. Clifford's research concerned the dynamic and kinetic behavior of nutrient metabolism as it occurs in vivo in humans. Nutrients of special interest include folate, vitamin E, β-carotene, lutein, and food (fruits/vegetables) components (flavonoids, isothiocyanates, catechins, sulfaraphanes, resveratrol). Foods rich in the above components protect against and hold promise for improved management of developmental, chronic, and degenerative diseases.

The research approach is to incorporate a 14C-label during the synthesis of the nutrient/component (commonly referred to as the tracer) and then to follow the fate of a minute oral dose (nmole amount) of the tracer over time since dosing using accelerator mass spectrometry that can measure attomole to zeptomole of 14C. The final step is to construct a kinetic and dynamic model that quantifies the behavior of the nutrient (folate or RRR-a-tocopherol) or compound using the tracer and the tracee datasets, the tracee is the endogenous nutrient or compound that is not labeled with 14C.

If the requirements of the nutrient/compound for specific metabolic functions can be stipulated, the minimum intake of nutrient or compound to sustain these critical functions can be determined. This could be particularly significant where nutrient or compound deficiency or marginal nutrition status is widespread. Simulation of the sudden cessation of dietary intake in a nutrient- or compound-replete person can identify and quantify some interesting features of the nutrient or compound system that are testable.

Positions and Employment
  • 1967-1969, Research Associate, Cornell University, Ithaca, NY
  • 1969-1972, Research Associate, MIT, Cambridge, MA
  • 1972-2022, Assistant, Associate, Full, Distinguished Professor, Department of Nutrition, UC Davis
  • 1983-1984, Sabbatical Leave at Differentiation Control Section, Laboratory of Cell Carcinogenesis and Tumor Promotion, NCI/NIH Bethesda, MD
  • 2001- 2007, Chair, Agric and Environmental Chem. Grad. Group, UC Davis
Other Experience and Professional Memberships
  • 1973 to 2022, Member, Graduate Group Nutritional Biology, Graduate advisor 2005-present
  • 1998 to 2022, Member, Graduate Group Agricultural & Environmental Chemistry, Chair 2001 – 2007
  • 2000 to 2009, Graduate Group in Biostatistics, Executive committee 2005 – 2009
  • 2000 to 2022, Fellow, American Society of Nutrition; Member, Editorial Board, Plant Food for Human Nutrition; Member, American Chemical Society
Selected Publications

Clifford AJ, Rincon G, Owens JE, Medrano JF, Moshfegh AJ, Baer DJ, Novotny JA. Single Nucleotide Polymorphisms in CETP, SLC46A1, SLC19A1, CD36, BCMO1, APOA5, and ABCA1 are significant predictors of plasma HDL in healthy adults. Lipids in Health and Disease. 2013; 12: 66. [PubMed] Open Access PDF

Novotny JA, Fadel JG, Holstege DM, Furr HC, Clifford AJ. This Kinetic, Bioavailability, and Metabolism Study of RRR-α-Tocopherol in Healthy Adults Suggests Lower Intake Requirements than Previous Estimates.J Nutr. 2012 Dec;142(12):2105-11. [PubMed] SciVee Pubcast

Clifford AJ, Chen K, McWade L, Rincon G, Kim S, Holstege DM, Owens JE, Liu B, Muller H, Medrano JF, Fadel JG, Moshfegh AJ, Baer DJ, Novotny JA. Gender and Single Nucleotide Polymorphisms in MTHFR, BHMT, SPTLC1, CRBP2, CETP, and SCARB1 Are Significant Predictors of Plasma Homocysteine Normalized by RBC Folate in Healthy Adults. J Nutr. 2012 Sep;142(9):1764-71. [PubMed]

Kim SH, Cruz GD, Fadel JG, Clifford AJ. Food Authenticity using Natural Carbon Isotopes (12C, 13C, 14C) in Grass-fed and Grain-fed Beef. Food Science and Biotechnology. 2012;21(1):295-298. Abstract.

Chuang JC, Matel HD, Nambiar KP, Kim S, Fadel JG, Holstege DM, Clifford AJ. Quantitation of [5-14CH3]-2R,4'R,8'R)-α-Tocopherol in Humans. J Nutr. 2011 Aug;141(8):1482-8. [PubMed]

Kim SH, Chuang JC, Kelly PB, Clifford AJ. Carbon Isotopes Profiles of Human Whole Blood, Plasma, Red Blood Cells, Urine and Feces for Biological/Biomedical 14C-Accelerator Mass Spectrometry Applications. Anal Chem. 2011:83(9):3312-3318. [PubMed]

Kim SH, Kelly PB, Clifford AJ. Calculating radiation exposures during use of 14C-labelled nutrients, food components, and biopharmaceuticals to quantify metabolic behavior in humans. J Agric Food Chem. 2010;58: 4632-37. [PubMed]

Kim SH, Kelly PB, Ortalan V, Browning ND, and Clifford AJ. Quality of Graphite Target for Biological/Biomedical/Environmental Applications of 14C-Accelerator Mass Spectrometry. Anal Chem. 2010;82:2243-52. [PubMed]

Kim SH, Kelly PB, and Clifford AJ. Accelerator mass spectrometry targets of submilligram carbonaceous samples using the high-throughput Zn reduction method. Anal Chem. 2009;81:5949-54. [PubMed]

Ho CC, de Moura FF, Kim SH, Burri BJ, Clifford AJ. A minute dose of 14C-β-carotene is absorbed and converted to retinoids in humans. J Nutr. 2009;139:1480-86. [PubMed]

Kim SH, Kelly PB, and Clifford AJ. Biological/Biomedical AMS targets Part-II: Their physical, morphological, and structural characteristics. Anal Chem 2008;80:7661-9. [PubMed]

Kim SH, Kelly PB, and Clifford AJ. Biological/Biomedical AMS targets Part-I; Optimizing the CO2 reduction step using Zinc. Anal Chem 2008;80:7651-60. [PubMed]

Owens JE, Clifford AJ, Bamforth CW. Folate in Beer. J Inst Brewing 2007;113:243-48. Abstract.

Clifford AJ, Owens JE, Fadel JG, Liu B, Müller HG, Medrano JFR, and Moghaddam B. Effect of genetic polymorphisms on the kinetics of in vivo human folate metabolism. In Mathematical Modeling in Nutrition and Agriculture. Eds Hannigan MD, Novotny JA, and Marstaller CL. Virginia Polytechnic Institute and State University. Blacksburg, VA 2007; 243-65. Chapter.

Ho CC, de Moura FF, Kim S-H, and Clifford AJ. Excentral cleavage of b-carotene in a healthy adult man.  Am J Clin Nutr. 2007;85:770-7. [PubMed]

Owens JE, Holstege DM, Noceti EM, and Andrew J. Clifford.  Comparison of two dietary folate intake instruments and their validation by RBC folate.  J Agric Food Chem. 2007;55:3737-40. [PubMed]

Owens JE, Holstege DM, Noceti EM, and Andrew J. Clifford.  High-throughput method for the quantitation of total folate in whole blood using LC-MS/MS.  J Agric Food Chem. 2007;55:3292-7. [PubMed]

Clifford AJ, Moura FF, Ho CC, Follett JR, Fadel JG, Vogel JS, and Novotny JA.  A feasibility study to quantify in vivo human a-tocopherol metabolism.  Am J Clin Nutrition 2006; 84:1430-41.[PubMed]

Getachew G, Burri BJ, Kelly P, Haack KW, Ognebene TJ, Buchholz BA, Vogel JS, and Clifford AJ.  How to convert biological and environmental carbon to graphite for AMS.  Radiocarbon 2006;48:325-36.

de Moura FF, Burri BJ, and Clifford AJ.  Accelerator mass spectrometry in the study of vitamins and mineral metabolism in humans.  Handbook of Vitamins.  Eds MCCormick DB, Rucker RB, Suttie JW, Zempleni J.  2006; Marcel Dekker, NY. Pp 545-557.

Moura FF, Ho CC, Getachew G, Hickenbottom S, and Clifford AJ.Kinetics of 14C distribution after tracer dose of 14C-lutein in an adult woman. Lipids 2005;40:1069-1073. [PubMed]

Owens JE, Holstege DM, and Clifford AJ.  Quantitation of total folate in whole blood using LC/MS/MS.  J Agricultural and Food Chemistry 2005;53:7390-7394. [PubMed]

Dueker SR, Lame M, Lin Y, Clifford AJ, Buchholz BA, and Vogel JS.  Traditional mass spectrometry for quantitation of human folate pools.  Trends in Food Sci and Technol.  2005;16:267-70.

Burri BY and Clifford AJ.  b-Carotene metabolism measured by accelerator mass spectrometry.  Sight and Life. 2005;1:6-8.

Ebeler SE, Dingley KH, Ubick E, Abel S, Mitchell AE, Burns SA, Steinberg FM, and Clifford AJ.  Animal models and analytical approaches for understanding the relationships between wine and cancer.  Drugs Exp Clin Res. 2005;31:19-27. [PubMed]

Clifford AJ, Lin Y, Noceti EM, Block-Joy A, Ho CC, Block T, and Block G.  Erythrocyte folate and its response to folic acid supplementation is assay dependent in women. J Nutr 2005;135:137-143. [PubMed]

Burri BY and Clifford AJ.  Carotenoid and retinoid metabolism: Insights from isotope studies.  Arch Biochem Biophysics.  2004; 430:110-119. [PubMed]

Ross SA, Srinivas PR, Clifford AJ, Lee SC, Philbert MA, Hettich RL.  New technologies for nutrition research.  J Nutr. 2004;134:681-685. [PubMed]

Koutsos EA, Clifford AJ, Calvert CC, and Klasing KC.  Maternal carotenoid status modifies the incorporation of dietary carotenoids into immune tissues of growing chickens (Gallus gallus domesticus).  J Nutrition 2003;133:1132-1138. [PubMed]

Yao F, Muller H-G, Clifford AJ, Dueker SR, Follett J, Lin Y, Buchholz BA, and Vogel JS.  Shrinkage estimation for functional component scores with application to the population kinetics of plasma folate.  Biometrics 2003, 59:676-685. [PubMed]

Lin Y, Dueker SR, Jones AD, and Clifford AJ.  Human whole blood folate analysis using a SIM GCMS protocol.  Anal Biochem 2003,312:255-257. [PubMed]

Lin Y, Dueker SR, Follett JR, Fadel JG, Arjomand A, Schneider PD, Miller JA, Green R, Buchholz BA, Vogel JS, Phair RD, and Clifford AJ.  Quantitation of in vivo human folate metabolism.  Am J Clin Nutrition 2004; 80:680-691. [PubMed]

Vogel JS, Dueker SR, Lin Y, Clifford AJ, Ognibene T, Hillegonds, and Buchholz BA.  Quantifying human vitamin kinetics with AMS.  In Synthesis and Applications of Isotopically Lableled Compounds. 2003:171-4.

Dingley KH, Ubick EA, Chiarappa-Zucca ML, Nowell S, Abel S, Ebeler SE, Mitchell AE, Burns SA, Steinberg FM, and Clifford AJ.  Effect of dietary constituents with chemoproventive potential on adduct formation of a low dose of the heterocyclic amines PhIP and IQ and phase II hepatic enzymes. Nutrition and Cancer 2003;46:212-221. [PubMed]

Lemke SL, Dueker SR, Follett JR, Lin Y, Carkeet C, Buchholz BA, Vogel JS, and Clifford AJ.  Absorption and retinol equivalence of b-carotene in humans is influenced by dietary vitamin A intake.  J Lipid Res 2003;44:1591-1600. [PubMed]

Mueller HG, Su CL, Dueker SR, Follett JR, Lin Y, Clifford AJ, Buchholz BA, and Vogel JS.  Semiparametric modeling of labeled cell kinetics, with application to isotope labeling erythrocytes.  Biometrics 2002;58:937-945. [PubMed]

Ebeler SE, Brenneman CA, Kim GS, Jewell WT, Webb MR, Chacon-Rodriguez L, MacDonald E, Cramer AC, Levi A, Islas A, Kraus A, Hinrichs SH, and Clifford AJ.  Dietary catechin delays tumor onset in a transgenic mouse model. Am J Clin Nutrition 2002, 76:865-872. [PubMed]

Hickenbottom SJ, Lemke SL, Dueker SR, Lin Y, Follett JR, Carkeet C, Buchholz BA, Vogel JA, and Clifford AJ.  Dual isotope test for assessing b-carotene cleavage to vitamin A in humans.  European J Clinical Nutrition 2002;41:141-147. [PubMed]

Lunetta JM, Zulim RA, Dueker SR, Lin Y, Flaig V, Schneider PD, Wolfe BM, and Clifford AJ. Method for the simultaneous determination of retinol and beta-carotene concentrations in human tissues and plasma.  Anal Biochem 2002, 304:100-109. [PubMed]

Hickenbottom SJ, Follett JR, Lin Y, Dueker SR, Burri BJ, Neidlinger TR, and Clifford AJ. Variability in conversion of ß-carotene to vitamin A in men measured using a double-tracer study design. Am J Clin Nutrition, 2002, 75:900-907. [PubMed]

Lin Y, Dueker SR, Jones AD, and Clifford AJ.  A parallel processing SPE protocol for the determination of whole blood folate.  Anal Biochem 2002, 301:14-20. [PubMed]