There are modest associations between higher lipid levels and circulating leukocyte counts in humans, according to study results published in the Journal of Clinical Lipidology.
Researchers used data from the Multi-Ethnic Study of Atherosclerosis to investigate the relationship between different lipid measures with different types of white blood cell (WBC) counts and to determine interaction, if any, with sex or race/ethnicity. Study participants included men and women aged 45 to 84 years who belonged to 4 different ethnic groups (non-Hispanic white, black, Hispanic American, and Asian) between July 2000 and August 2002 (N=6814).
Participants selected for this analysis underwent 4 follow-up assessments over a period of 10 years (n=2873), which included total WBC and subfraction counts collected from fasting venous blood samples. The investigators analyzed total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and triglycerides; basophil, eosinophil, lymphocyte, monocyte, and neutrophil counts had been measured previously.
In a fully adjusted model, a higher TC level was associated with a lower natural-log-transformed (ln) total WBC count after adjusting for multiple testing correction (B=-0.028; P <.001), with a 2.8% lower cell count per 1-standard deviation (SD) increase in TC level. By WBC type, a higher TC level was significantly associated with a lower ln-transformed monocyte count (B=-0.038; P ≤.001) and neutrophil count (B=-0.034; P ≤.001), with 3.7% and 3.4% lower cell count, respectively, per 1-SD increase in TC level.
A higher LDL-C level was significantly associated with a lower ln-transformed total WBC count in the full adjustment model (B=-0.023; P <.001), with a 2.3% lower cell count per 1-SD increase in LDL-C level; a higher LDL-C level was also significantly associated with a lower ln-transformed monocyte count (B=-0.031; P <.001) and neutrophil count (B=-0.028; P <.002), with 3% and 2.7% lower cell counts, respectively. No significant interactions with sex and race/ethnicity were found among TC, high-density lipoprotein cholesterol, LDL-C, or triglyceride counts.
Although these significant associations between plasma lipid levels and WBC populations were observed, the heterogeneous and modest nature of these relationships makes it difficult to support the hypothesis that lipids are in the causal pathway for leukogenesis.
Limitations of this study included the inability to definitively determine familial hypercholesterolemia status of patients in the study and the underrepresentation of Chinese Americans compared with the original parent cohort. The WBC profiles were measured only at examination 5 and not at baseline examination 1, so researchers were unable to assess the temporal relationship between changes in lipid measures and change in WBC counts and inflammation status.
To the researchers’ knowledge, this study has the largest multi-ethnic study design that has assessed the relationship between lipid measures and different WBC counts. Future studies in other clinical settings are needed to confirm the findings of this study, which suggest modest associations between lipid levels and circulating leukocyte counts. The relative contribution of lipids and inflammatory factors that drive atherosclerosis remains an open question.
Lai YC, Woollard KJ, McClelland RL, et al. The association of plasma lipids with white blood cell counts: results from the multi-ethnic study of atherosclerosis [published online July 15, 2019]. J Clin Lipidol. doi:10.1016/j.jacl.2019.07.003