Non-Linear Association Between Red Blood Cell Folate and Visceral Adiposity in U.S. Adults Examined in Cross-Sectional Study

A study conducted at Jiangmen Central Hospital (China) aimed to determine the association between red blood cell (RBC) folate and visceral adipose tissue in young and middle-aged U.S. adults, focusing on the folate’s potential role as a determinant of visceral adiposity. This new study is based on previous research that linked RBC folate levels to obesity. RBC folate levels were quantified using a multi-step process combining microbiologic assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A paper based on this research was published in Frontiers in Nutrition (1).

Associated with an increased risk of a variety of non-communicable diseases (including diabetes, non-alcoholic steatohepatitis, cardiovascular diseases, gout, and various cancers), obesity has emerged as a critical public health concern because of its increasing global prevalence (2–5). Recently, obesity has been defined as a condition distinguished by characterized by an increase in body fat, with clinical obesity particularly acknowledged as a chronic, systemic illness where increased body fat leads to damage of organs, tissue, possibly leading to cardiovascular disease and kidney failure. This revised definition focuses on the need for more thorough methods of assessment of the condition besides body mass index (BMI), as well as more direct measures of body fat and its impact on functional health (6).

Folate, also known as vitamin B9, refers to a group of water-soluble compounds which are essential for a variety of physiological functions, including synthesis of DNA, cell division, and the prevention of neural tube defects (7,8). While naturally occurring folates can be found in leafy green vegetables, legumes, and citrus fruits, mandatory fortification of enriched cereal grains was authorized the United States in 1996 and fully implemented two years later (9,10). Public health concerns have shifted over time from thinking that not enough folates were being taken in through diet, to there being an excessive intake with associated risks (11).

This study utilized data from 7591 individuals taken from four cycles of the National Health and Nutrition Examination Survey (NHANES) conducted between 2011–2012, 2013–2014, 2015–2016, and 2017–2018, managed by the Centers for Disease Control and Prevention (CDC). For each of these cycles, RBC folate was assessed using a multi-step process. First, whole blood folate concentration was measured using a microbiologic assay, followed by an adjustment for RBC volume. Serum total folate concentration, calculated as the sum of individual serum folate forms, was then used to correct the RBC folate values.

Individual serum folate forms were quantified using liquid chromatography–tandem mass spectrometry (LC–MS/MS), resulting in RBC folate levels positively associated with VAT mass. A J-shaped dose–response relationship was observed with a threshold effect identified at an RBC folate level of 397.18 ng/mL. Below this threshold, the association was negative, while above the threshold, the association became positive (1).

The researchers wrote that their work identified the non-linear relationship between RBC folate levels and VAT, with a threshold effect at an RBC folate level of 397.18 ng/mL. Their findings, stress the need for further research to shed light on the mechanisms underlying that relationship, especially in the context of obesity and metabolic disturbances, they wrote. Although RBC folate holds the potential to be a biomarker for metabolic risk, the researcher state that longitudinal studies are necessary in establishing a connection between changes in folate status and VAT accumulation, and how those changes may affect that accumulation (1).

References

1. Jiang, C.; Li, J.; Yu, H. et al. Red Blood Cell Folate and Visceral Adipose Tissue Among Young and Middle-Aged American Adults. Front. Nutr. 2025, 12, 1512410. DOI: 10.3389/fnut.2025.151241
2. GBD 2015 Obesity Collaborators; Afshin, A.; Forouzanfar, M. H. et al. Health Effects Overweight and Obesity in 195 Countries over 25 Years. N. Engl. J. Med. 2017, 377 (1), 13-27. DOI: 10.1056/NEJMoa1614362
3. Polyzos, S. A.; Kountouras, J.; Mantzoros, C. S. Obesity and Nonalcoholic Fatty Liver Disease: From Pathophysiology to Therapeutics. Metabolism 2019, 92, 82-97. DOI: 10.1016/j.metabol.2018.11.014
4. Brown, O. I.; Drozd, M.; McGowan, H. et al. Relationship Among Diabetes, Obesity, and Cardiovascular Disease Phenotypes: A UK Biobank Cohort Study. Diabetes Care 2023, 46 (8), 1531-1540. DOI: 10.2337/dc23-0294
5. Avgerinos, K. I.; Spyrou, N.; Mantzoros, C. S. et al. Obesity and Cancer Risk: Emerging Biological Mechanisms and Perspectives. Metabolism 2019, 92, 121-135. DOI: 10.1016/j.metabol.2018.11.001
6. Rubino, F.; Cummings, D. E.; Eckel, R. H. et al. Definition and Diagnostic Criteria of Clinical Obesity. Lancet Diabetes Endocrinol. 2025, 13 (3), 221-262. DOI: 10.1016/S2213-8587(24)00316-4
7. Shulpekova, Y.; Nechaev, V.; Kardasheva, S. et al. The Concept of Folic Acid in Health and Disease. Molecules 2021, 26 (12), 3731. DOI: 10.3390/molecules26123731
8. Chen, X.; Zhang, Y.; Chen, H. et al. Association of Maternal Folate and Vitamin B₁₂ in Early Pregnancy with Gestational Diabetes Mellitus: A Prospective Cohort Study. Diabetes Care 2021, 44 (1), 217-223. DOI: 10.2337/dc20-1607
9. Subcommittee on Upper Reference Levels of Nutrients, Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, its Panel on Folate, Other B Vitamins, & Choline. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. 2000. http://www.ncbi.nlm.nih.gov/books/NBK114310/
10. Crider, K. S.; Bailey, L. B.; Berry, R. J. Folic Acid Food Fortification-Its History, Effect, Concerns, and Future Directions. Nutrients 2011, 3 (3), 370-384. DOI: 10.3390/nu3030370
11. Fardous, A. M.; Heydari, A. R. Uncovering the Hidden Dangers and Molecular Mechanisms of Excess Folate: A Narrative Review. Nutrients 2023, 15 (21), 4699. DOI: 10.3390/nu15214699