Research Blog

May 22, 2024

Mineral Biomarkers: RBC Selenium

Optimal Takeaways

Selenium is an essential micronutrient that counteracts oxidative stress, inflammation, and heavy metal toxicity. It supports metabolic detoxification, cardiovascular health, and active thyroid hormone production.

Selenium insufficiency can compromise these functions, and low red blood cell selenium may be associated with inflammation, autism, Alzheimer’s disease, heavy metal toxicity, and thyroid disorders. Excess selenium may be associated with lipid disorders, hair loss, dermatitis, and brittle hair and nails.

Red blood cell selenium reflects long-term exposure, while serum selenium reflects current intake.

Standard Range: 120-300 1.52 – 3.8 umol/L

The ODX Range: 135 - 255 ug/L (1.71 – 3.23 umol/L)

Low or insufficient selenium status may be associated with cardiomyopathy, mercury toxicity, increased T4, decreased T3, inflammatory conditions, oxidative stress, reduced immune function, increased cancer and heart disease risk (Gropper 2021), stroke (Hu X, 2019), compromised cognitive function, dysfunction of selenoproteins, Keshan disease, Kashin-Beck disease, insulin resistance (McCann 2011), smoking, iron deficiency anemia (Al-Mubarak 2022), myocarditis, decreased natural killer cells, compromised neutrophil function, reduced conversion of T4 to T3 (Fairweather-Tait 2011), hypothyroidism, enlarged thyroid, thyroid cancer, and autoimmune thyroiditis (Rayman 2019).  

Red blood cell selenium may be decreased in inflammation (Veldscholte 2024, Berger 2023, Costa 2014), alcoholic cirrhosis, cancer, chronic renal failure, stable chronic disease, aging over 60 years (Miller 1983), high-level athletic training (Maynar 2020), autism, heavy metal toxicity (El-Ansary 2017), oxidative stress, Alzheimer’s disease (Cardoso 2017), and may be associated with increased mortality in critically ill subjects in septic shock (Costa 2014).

High or excess selenium may be associated with selenium toxicity, increased risk of diabetes, hypertension, cancer (Gropper 2021), alopecia, dermatitis (Rayman 2018), dyslipidemia (Huang 2020), pulmonary edema, brittle hair and nails, and garlic odor emanating from the skin and breath (Fairweather-Tait 2011).


The trace mineral selenium is vital to glutathione and antioxidant activity, detoxification, immune function, inflammation regulation, reproductive health, and thyroid hormone metabolism (Avery 2018). Selenium is required for several antioxidant enzymes and the deiodinase enzymes that convert T4 to T3, the most biologically active thyroid hormone (Gropper 2021, Fairweather-Tait 2011).

Selenium insufficiency can lead to oxidative stress and a pro-inflammatory immune response that further exacerbates thyroid dysfunction. Balanced selenium status is crucial to managing Hashimoto’s and Graves’ thyroid disorders (Duntas 2015). Insufficiency is also associated with increased cardiovascular mortality risk (Alehagen 2016).

Selenium status is often evaluated by measuring serum or plasma levels. However, this may not be ideal under certain circumstances. Inflammation can significantly divert micronutrients, including selenium, iron, zinc, thiamin, folate, cobalamin, and vitamins A, C, and D, and falsely decrease serum levels. In such cases, RBC selenium may be more accurate. Concurrent C-reactive protein (CRP) measurement is recommended for evaluating selenium status when inflammation is present (Berger 2023).

Research on 67 critical pediatric subjects revealed plasma selenium was significantly lower than the standard reference range, while RBC selenium was within range. Plasma selenium correlated inversely with CRP, suggesting the diversion of selenium from the plasma during inflammation (Veldscholte 2024).

Red blood cell selenium may decrease significantly with aging (over 60 years), alcoholic cirrhosis, malignancy, chronic renal failure, and stable chronic disease (Miller 1983).

Early research on 199 healthy Polish subjects observed that mean selenium levels in whole blood versus plasma versus RBCs were 96.9–104.2 ug/L (1.23-1.32 umol/L), 75.1–80.1 ug/L (0.95-1.02 umol/L), and 128.3–137.7 ug/L (1.63-1.75), respectively. Levels were higher in men than women. Researchers note the results in this population were lower than elsewhere in Europe, likely due to decreased dietary selenium intake (Wasowicz 1987).

Selenium can counteract heavy metals, including mercury and lead. Significantly lower selenium was found in the red blood cells of autistic children, who also had significantly higher mercury and lead (El-Ansary 2017).

One research study of 36 individuals with Alzheimer’s and 39 controls found that those with Alzheimer’s had significantly lower RBC selenium than healthy controls even though serum levels did not differ. Alzheimer’s disease is associated with heavy metal toxicity, oxidative stress, and inflammation, as well as low RBC selenium (Cardoso 2017).

Red blood cell selenium reflects longer-term exposure than serum selenium, which only reflects current intake. Supplementation can improve selenium status and associated metabolic functions but should be carried out with caution, as excess selenium can have detrimental effects, including increased diabetes, hypertension, and cancer risk (Gropper 2021), alopecia, dermatitis (Rayman 2018), dyslipidemia (Huang 2020), pulmonary edema, brittle hair and nails, and garlic odor emanating from the skin and breath (Fairweather-Tait 2011).

New call-to-action


Alehagen, Urban et al. “Supplementation with Selenium and Coenzyme Q10 Reduces Cardiovascular Mortality in Elderly with Low Selenium Status. A Secondary Analysis of a Randomised Clinical Trial.” PloS one vol. 11,7 e0157541. 1 Jul. 2016, doi:10.1371/journal.pone.0157541

Al-Mubarak, Ali A et al. “High selenium levels associate with reduced risk of mortality and new-onset heart failure: data from PREVEND.” European journal of heart failure vol. 24,2 (2022): 299-307. doi:10.1002/ejhf.2405

Avery, Joseph C, and Peter R Hoffmann. “Selenium, Selenoproteins, and Immunity.” Nutrients vol. 10,9 1203. 1 Sep. 2018, doi:10.3390/nu10091203

Berger, Mette M et al. “Pitfalls in the interpretation of blood tests used to assess and monitor micronutrient nutrition status.” Nutrition in clinical practice : official publication of the American Society for Parenteral and Enteral Nutrition vol. 38,1 (2023): 56-69. doi:10.1002/ncp.10924

Cardoso, Bárbara R et al. “Selenium Levels in Serum, Red Blood Cells, and Cerebrospinal Fluid of Alzheimer's Disease Patients: A Report from the Australian Imaging, Biomarker & Lifestyle Flagship Study of Ageing (AIBL).” Journal of Alzheimer's disease : JAD vol. 57,1 (2017): 183-193. doi:10.3233/JAD-160622

Costa, Nara Aline et al. “Erythrocyte selenium concentration predicts intensive care unit and hospital mortality in patients with septic shock: a prospective observational study.” Critical care (London, England) vol. 18,3 R92. 7 May. 2014, doi:10.1186/cc13860

Duntas, L H. “The Role of Iodine and Selenium in Autoimmune Thyroiditis.” Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme vol. 47,10 (2015): 721-6. doi:10.1055/s-0035-1559631

El-Ansary, Afaf et al. “Relationship between selenium, lead, and mercury in red blood cells of Saudi autistic children.” Metabolic brain disease vol. 32,4 (2017): 1073-1080. doi:10.1007/s11011-017-9996-1

Fairweather-Tait, Susan J et al. “Selenium in human health and disease.” Antioxidants & redox signaling vol. 14,7 (2011): 1337-83. doi:10.1089/ars.2010.3275

Gropper, Sareen S.; Smith, Jack L.; Carr, Timothy P. Advanced Nutrition and Human Metabolism. 8th edition. Wadsworth Publishing Co Inc. 2021.

Hu, Xue Feng et al. “Circulating Selenium Concentration Is Inversely Associated With the Prevalence of Stroke: Results From the Canadian Health Measures Survey and the National Health and Nutrition Examination Survey.” Journal of the American Heart Association vol. 8,10 (2019): e012290. doi:10.1161/JAHA.119.012290

Huang, Yu-Qing et al. “Association of circulating selenium concentration with dyslipidemia: Results from the NHANES.” Journal of trace elements in medicine and biology : organ of the Society for Minerals and Trace Elements (GMS) vol. 58 (2020): 126438. doi:10.1016/j.jtemb.2019.126438

Maynar, M et al. “Erythrocyte concentrations of chromium, copper, manganese, molybdenum, selenium and zinc in subjects with different physical training levels.” Journal of the International Society of Sports Nutrition vol. 17,1 35. 9 Jul. 2020, doi:10.1186/s12970-020-00367-4

McCann, Joyce C, and Bruce N Ames. “Adaptive dysfunction of selenoproteins from the perspective of the triage theory: why modest selenium deficiency may increase risk of diseases of aging.” FASEB journal : official publication of the Federation of American Societies for Experimental Biology vol. 25,6 (2011): 1793-814. doi:10.1096/fj.11-180885  

Miller, L et al. “Red blood cell and serum selenium concentrations as influenced by age and selected diseases.” Journal of the American College of Nutrition vol. 2,4 (1983): 331-41. doi:10.1080/07315724.1983.10719930

Rayman, Margaret P et al. “Effect of long-term selenium supplementation on mortality: Results from a multiple-dose, randomised controlled trial.” Free radical biology & medicine vol. 127 (2018): 46-54. doi:10.1016/j.freeradbiomed.2018.02.015

Rayman, Margaret P. “Multiple nutritional factors and thyroid disease, with particular reference to autoimmune thyroid disease.” The Proceedings of the Nutrition Society vol. 78,1 (2019): 34-44. doi:10.1017/S0029665118001192

Veldscholte, K et al. “Plasma and red blood cell concentrations of zinc, copper, selenium and magnesium in the first week of paediatric critical illness.” Clinical nutrition (Edinburgh, Scotland) vol. 43,2 (2024): 543-551. doi:10.1016/j.clnu.2024.01.004

Wasowicz, W, and B A Zachara. “Selenium concentrations in the blood and urine of a healthy Polish sub-population.” Journal of clinical chemistry and clinical biochemistry. Zeitschrift fur klinische Chemie und klinische Biochemie vol. 25,7 (1987): 409-12. doi:10.1515/cclm.1987.25.7.409

Tag(s): Biomarkers

Other posts you might be interested in