Associations of obesity and body shape with erythrocyte and reticulocyte parameters in the UK Biobank cohort

Background Obesity is associated with type 2 diabetes mellitus and chronic low-grade inflammation. Although chronic inflammatory conditions and diabetes are associated with anaemia, less is known about associations of obesity and body shape, independent of each other, with erythrocyte and reticulocyte parameters. Methods We investigated the associations of body mass index (BMI) and the allometric body shape index (ABSI) and hip index (HI), which are uncorrelated with BMI, with erythrocyte and reticulocyte parameters (all continuous, on a standard deviation (SD) scale) in UK Biobank participants without known metabolic, endocrine, or major inflammatory conditions (glycated haemoglobin HbA1c < 48 mmol/mol, C-reactive protein CRP < 10 mg/L). We examined erythrocyte count, total reticulocyte count and percent, immature reticulocyte count and fraction (IRF), haemoglobin, haematocrit, mean corpuscular haemoglobin mass (MCH) and concentration (MCHC), mean corpuscular and reticulocyte volumes (MCV, MRV), and red cell distribution width (RDW) in multivariable linear regression models. We additionally defined body shape phenotypes with dichotomised ABSI (>= 73 women; >= 80 men) and HI (>= 64 women; >= 49 men), including pear (small-ABSI-large-HI) and apple (large-ABSI-small-HI), and examined these in groups according to BMI (18.5-25 normal weight; 25-30 overweight; 30-45 kg/m(2) obese). Results In 105,853 women and 100,854 men, BMI and ABSI were associated positively with haemoglobin, haematocrit, and erythrocyte count, and more strongly with total reticulocyte count and percent, immature reticulocyte count and IRF. HI was associated inversely with all, but least with IRF. Associations were comparable in women and men. In groups according to obesity and body shape, erythrocyte count was similar to 0.6 SD higher for obese-apple compared to normal-weight-pear phenotype (SD = 0.31*10(12)/L women, SD = 0.34*10(12)/L men), total reticulocyte count was similar to 1.1 SD higher (SD = 21.1*10(9)/L women, SD = 23.6*10(9)/L men), immature reticulocyte count was similar to 1.2 SD higher (SD = 7.9*10(9)/L women, SD = 8.8*10(9)/L men), total reticulocyte percent was similar to 1.0 SD higher (SD = 0.48% women and men), and IFR was over 0.7 SD higher (SD = 5.7% women and men). BMI but not ABSI or HI was associated more weakly inversely with MCV, MRV, and MCH, but positively with MCHC in men and RDW in women. Conclusions In obesity uncomplicated with diabetes, larger BMI and ABSI are associated with increased erythropoiesis and reticulocyte immaturity.

Automated summary

This study investigated the associations of obesity and body shape with erythrocyte and reticulocyte parameters. The results showed that both obesity and body shape are positively associated with erythrocyte and reticulocyte parameters. This suggests that obesity may increase erythropoiesis and reticulocyte immaturity.