The mediating effect of immune-inflammatory indices in shift work and hypertension: a cohort study in China

OBJECTIVES: Global hypertension prevalence is increasing. Studies of the association of shift work with hypertension have produced inconsistent results, and the role of immune-inflammatory indices in this link remains unclear. This study aimed to clarify the association of shift work with hypertension and to identify the mediating effects of immune-inflammatory indices on hypertension. METHOD: This cohort study assessed 1322 oil workers, with baseline data collected from 2013-2015 and final follow-up in 2023. The definition of shift work was in accordance with the International Labor Organization's Convention on Night Work (No. 171). Hypertension was diagnosed according to the Chinese Hypertension Prevention and Treatment Guidelines (2018 revised edition). Smooth curve fitting, piecewise regression modeling, and the Karlson-Holm-Breen method were used to analyze the associations among immune-inflammatory indices and hypertension. RESULTS: Shift work was associated with hypertension [two-shift: risk ratio (RR) 1.75, 95% confidence interval (CI) 1.27-2.05; three-shift: RR 1.75, 95% CI 1.10-2.34; four-shift: RR 1.57, 95% CI 1.10-2.14] and elevated immune-inflammatory index [logarithmic (ln) Systemic Immune-Inflammation Index (SII) 0.18, 95% CI 0.10-0.26, Pan Immune-Inflammation Value (PIV) 0.15, 95% CI 0.06-0.23, neutrophil-lymphocyte ratio (NLR) 0.17, 95% CI 0.10-0.24, Systemic Inflammation-Response Index (SIRI) 0.14, 95% CI 0.06-0.22, and platelet-lymphocyte ratio (PLR) 0.05, 95% CI 0.01-0.09]. Cumulative night shifts were associated with hypertension (1-220 nights: RR 2.57, 95% CI 1.26-5.26; 220-660 nights: RR 1.78, 95% CI 1.08-2.95; ≥660 nights: RR 2.02, 95% CI 1.22-2.13). Cumulative night shift exposure levels exerted varying effects impacted immune-inflammatory indices. The SII, PIV, NLR, SIRI, and monocyte-lymphocyte ratio (MLR) were independently associated with hypertension risk (RR 1.82, 95% CI 1.47-2.22; RR 1.85, 95% CI 1.53-2.19; RR 2.04, 95% CI 1.60-2.54; RR 2.03, 95% CI 1.64-2.48; RR 1.85, 95% CI 1.27-2.59). The mediating effects of ln(SII), ln(PIV), ln(NLR), ln(SIRI), and composite inflammatory index were 17.52%, 17.51%, 17.78%, 18.64%, and 21.94%, respectively. CONCLUSION: Shift work and elevated immune-inflammatory indices were associated with hypertension. Immune-inflammatory indices mediate the association between shift work and hypertension. Therefore, hypertension monitoring should be strengthened among shift workers and immune-inflammatory markers should be considered for early hypertension detection. Future targeted intervention trials are warranted.