Shift work a risk factor for kidney stones

A recent study suggests a positive association between shift work and risk of kidney stone events, with lifestyle factors partially mediating the association.

In this study, shift work was defined as a work schedule outside regular daytime hours of 9 AM to 5 PM. This may include afternoon or night shifts, or rotations between these schedules. [Mayo Clin Proc 2025;100:1731-1744]

The risk of kidney stone events was higher among individuals who sometimes (hazard ratio [HR], 1.09; p=0.20) and usually or always (HR, 1.19; p=0.003) worked shifts than those who never did.

In the fully adjusted model, shift work was associated with a significantly higher risk of kidney stone events (HR, 1.15; p=0.004), which was more pronounced among night shift workers (HR, 1.22; p=0.001). Night shift was defined as a work schedule during regular sleeping hours (from 12 AM to 6 AM).

Subgroup analyses

There were more pronounced associations in younger participants (<50 vs >50 years; HRs, 1.32 vs 1.14; p_interaction=0.04) and among those who never or rarely did heavy manual labour vs those who did sometimes or more (HRs, 1.27 vs 1.10; p_interaction=0.03).

The investigators attributed the latter finding to differences in fluid intake and loss among individuals who do and minimally do heavy manual labour. Individuals who do not usually engage in heavy manual labour may have lower fluid intake, which may explain the stronger association.

Conversely, those engaged in heavy manual labour tend to have increased fluid intake. “[This] may offset their higher fluid losses by diluting the urine, thereby reducing the risk of kidney stone formation,” the researchers explained.

Potential mediators: Lifestyle factors

Current smoking, unhealthy sleep duration (ie, sleeping >9 or <7 hrs), unhealthy sedentary time (ie, >4 hrs of television daily), and BMI were associated with higher risks of kidney stone events (HRs, 1.31, 1.13, 1.18, and 1.06, respectively).

Smoking and unhealthy sleep duration are associated with increased reactive oxygen-induced oxidative stress and immune dysregulation driven by inflammation, which contribute to the formation of renal calcium oxalate crystals. [Mutat Res Rev Mutat Res 2021;787:108365; Nutrients 2023;15:1518; Nat Rev Nephrol 2021;17:417-433; Biochim Biophys Acta Mol Basis Dis 2022;1868:166442]

These findings suggest that these unhealthy lifestyle factors could mediate the association between shift work and kidney stone events, the researchers said. “If these mediations were causal, interventions on these modifiable lifestyles could reduce the incidence of kidney stone events in shift workers. Our mediation analyses suggest that implementing flexible work schedules may help mitigate circadian rhythm disruptions associated with shift work.”

Conversely, fluid intake was associated with a lower risk of kidney stone events (HR per 100 mL increase of fluid intake per day, 0.98). High fluid intake increases urinary flow, which can subsequently reduce crystallization, crystal cell adhesion, and crystal aggregation, thereby increasing crystal elimination. [Clin Chem Lab Med 2005;43:585-589; J Vet Sci 2016;17:269-277]

Healthy lifestyle is key

The study included 226,459 participants (mean age 52.55 years, 50.7 percent women, mean BMI 27.16 kg/m²) from the UK Biobank who did not have a kidney stone at baseline. Of these, 36,537 (16.13 percent) reported shift work. During a median follow-up of 13.7 years, 2,893 participants had kidney stone events.

“[Taken together, the] results suggest that shift work should be considered in kidney stone prevention, especially for shift workers <50 years,” the researchers said. The study also underscores the need to promote healthy lifestyles to reduce kidney stone incidence among shift workers and improve their health.

Health promotion initiatives in the workplace could include educational programmes focusing on the importance of increased fluid intake, weight management, healthy sleep habits, reduced sedentary time, and smoking cessation, they added.