Does night shift work increase osteoporosis risk?

By Dr. Priyom Bose, Ph.D.Reviewed by Lauren HardakerJan 15 2026

Analysis of more than 270,000 UK adults shows that working through the night, especially on a long-term basis, is linked to weaker bones and higher fracture risk, highlighting an overlooked occupational health concern.

Study: Association between night shift work and risk of osteoporosis and osteoporosis-related pathological fracture. Image credit: Pixel-Shot/Shutterstock.com

A recent study in Frontiers in Public Health examined the association between night shift work and osteoporosis (OP) and its related fracture risks. In comparison to day workers, those engaged in usual or permanent night shift work, and to a lesser extent, individuals with past night shift exposure, are associated with a higher risk of developing osteoporosis.

Prevalence and factors leading to osteoporosis

Osteoporosis (OP) is a widespread systemic skeletal disorder characterized by decreased bone density and structural deterioration that makes bones weak, brittle, and susceptible to fractures. Since this condition may develop without any symptoms, it is considered a “silent disease”. In most cases, OP occurs in the hip, spine, or wrist.

Several factors accelerate bone degradation, including age-related bone loss and hormonal shifts, particularly the decline in estrogen during menopause. In addition, genetic predisposition, low body mass index (BMI), prolonged use of certain medications, and lifestyle choices including smoking, excessive alcohol consumption, and physical inactivity all elevate risk.

According to the National Center for Health Statistics (NCHS), more than half of U.S. adults aged 50 and older have OP or are at increased risk due to declining bone mass. The American Academy of Orthopedic Surgeons (AAOS) emphasizes that effective primary prevention strategies, such as physical activity, lifestyle modifications, and, in some cases, orthopedic medications, can significantly reduce OP incidence by mitigating bone mineral density loss. Given this burden, identifying novel risk factors for osteoporosis remains a critical research priority.

The effect of shift work on health

Human physiological functions are regulated by an inherent circadian rhythm that optimizes biological processes in alignment with daily environmental and behavioral patterns. Shift work, defined as employment outside conventional daytime hours, significantly disrupts circadian rhythms and sleep cycles. Night shift work is typically defined as working at least three hours between midnight and 6 a.m.

Working in variable shifts has significantly increased in developed countries. For instance, previous research estimates that approximately 21 % of EU and 29 % of US employees are engaged in shift work.

Multiple studies have shown that prolonged and frequent night shift work can disrupt metabolic functions and hormonal secretion, thereby increasing susceptibility to chronic diseases. While research links night shifts to obesity, aging issues, and heart disease, the connection to OP remains less well established.

Assessing whether night shift work influences OP

The current study recruited employed or self-employed participants with night shift exposure from the UK Biobank, which contains over 500,000 individuals aged approximately 40 to 69 years. Any participant with pre-existing osteoporosis was excluded.

At baseline, participants reported their work schedules and were classified as day workers, working from 9 a.m. to 5 p.m., or shift workers, working in the afternoon, evening, night, or on a mixed-shift rotation. Based on frequency responses, they were further grouped as day workers, shift but never or rarely night shifts, some night shifts, or usual or permanent night shifts.

The lifetime employment data were used to assess whether the duration, total years, and frequency, average number of night shifts per month, of night shift work correlate with OP risk, the primary outcome. In addition, this study assessed whether night shift work interacts with genetic predisposition to influence OP susceptibility. Researchers also evaluated the association between night shift work and OP-related pathological fractures, the secondary outcome. Cox proportional hazards models were used to assess the hazard ratios (HR) for the association between current night shift work and incident osteoporosis.

Current and past night shift increases OP risks

After screening, 276,774 participants with 5,906 OP events were analyzed: day workers (82.7 %), shift workers rarely doing nights (8.5 %), some night shifts (4.9 %), and usual or permanent night shifts (3.8 %). Night shift workers were more likely to be male, younger, less educated, with longer work hours, greater socio-economic disadvantage, non-European ethnicity, higher BMI, elevated diabetes prevalence, shorter sleep, and later chronotypes.

Cox models showed that higher night shift exposure categories were generally associated with increased OP risk, with usual night shift workers at the highest risk. Multivariable models confirmed this trend, although the strongest and most statistically robust association was observed among usual or permanent night shift workers. Restricting analyses to OP incidents occurring two or more years after baseline strengthened the association. Usual night shift work also increased OP-related pathological fracture risk, with an HR of approximately 1.9.

Analysis of rotating night shifts before baseline included 75,120 participants, of whom 806 had OP. When lifetime exposure was assessed by total duration, cumulative years of night shift work were generally positively associated with OP odds. In the age-, sex-, and BMI-adjusted model, participants working night shifts for less than five years had a higher OP likelihood than never workers.

Multivariable adjustment suggested a higher risk with longer exposure durations, although estimates for more than 10 years of night shift work were modest and not statistically significant. When lifetime exposure was assessed by frequency, working an average of 3–8 night shifts per month showed the clearest increase in OP risk compared with never workers, highlighting a non-linear pattern of risk.

Sensitivity analyses adjusting for missing values, chronic diseases, cancer, sleep factors, outdoor time, supplements, and female-specific variables did not materially modify these associations, supporting the robustness of the observed night shift, OP relationship. Stratified analyses found no significant interactions between sex, BMI, sleep chronotype, sleep duration, or other AAOS confounders and night shift status, current or lifetime, on OP risk, indicating that the associations were broadly consistent across these subgroups.

Polygenic Risk Score (PRS) was positively correlated with OP risk, indicating a higher risk with higher PRS. No significant interactions between genetic susceptibility and night shift variables were found for OP risk.

Conclusion

This study demonstrates a significant positive association between usual or long-term night shift work and increased risk of osteoporosis and OP-related pathological fractures, independent of genetic susceptibility. As an observational analysis, the findings indicate association rather than causation, but they nonetheless highlight the potential value of targeted bone health screening and preventive interventions among night shift workers.

Although the relative risk was elevated, the absolute risk of osteoporosis for any individual worker remained low. These results suggest that occupational health policies could consider incorporating regular bone density monitoring and lifestyle modifications to help mitigate osteoporosis risk in this vulnerable population.

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