Does night work increase the risk of osteoporosis?

The analysis of more than 270,000 adults in the UK shows that working at night, especially over the long term, is linked to weaker bones and a higher risk of fracture, highlighting a neglected occupational health concern.

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

A recent study in Frontiers in Public Health examined the relationship between night work and osteoporosis (OP) and associated fracture risks. Compared to day workers, those engaged in habitual or permanent night work, and to a lesser extent, those with prior night shift exposure, are associated with a higher risk of osteoporosis.

Prevalence and factors leading to osteoporosis

osteoporosis (OP) is a widespread systemic skeletal disorder characterized by reduced bone density and structural deterioration that renders bones weak, brittle, and prone to fracture. Since this condition can develop without symptoms, it is considered a “silent disease.” In most cases, OP occurs in the hip, spine or wrist.

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

According to the National Center for Health Statistics (NCHS), more than half of US adults age 50 and older have OP or are at increased risk due to decreased 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 effect by mitigating bone loss. Given this burden, identifying new risk factors for osteoporosis remains a critical research priority.

The effect of shift work on health

Human physiological functions are regulated by an intrinsic 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 work is usually defined as working at least three hours between midnight and 6am

Shift work has increased significantly in developed countries. For example, previous research estimates that about 21% of EU and 29 % of US workers are employed in shifts.

Many 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 problems and heart disease, the link with OP remains less well established.

Assessment of whether night shift work affects OP

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

At baseline, participants reported their work hours and were classified as day workers, working from 9 A.M. until 5 p.m. or as shift workers, who worked in the afternoon, evening, night or rotating shifts. Based on frequency responses, they were further grouped as day workers, shift workers but never or rarely night shifts, some night shifts, or usual or permanent night shifts.

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

Current and previous night shift increases OP risks

After screening, 276,774 participants with 5,906 OP Events were analyzed: day workers (82.7 %), workers with occasional night shifts (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, working longer hours, greater socioeconomic disadvantage, non-European ethnicity, higher BMIincreased prevalence of diabetes, less sleep and later chronotypes.

Cox models showed that higher night shift exposure categories were generally associated with increased OP risk, with regular night shift workers at the highest risk. Multivariate models confirmed this trend, although the strongest and most statistically robust association was observed among habitual or permanent night shift workers. Limit analyzes to OP events occurring two or more years after baseline strengthened the association. The usual night work also increased OP-related risk of pathological fracture, with a HR about 1.9.

The pre-baseline rotating night shift analysis included 75,120 participants, of whom 806 had OP. When lifetime exposure was assessed based on total duration, cumulative night-shift work years were generally positively associated with OP chance. In age-, sex- and BMI-adjusted model, participants who had worked night shifts for less than five years had a higher OP chances than ever workers.

Multivariable adjustment suggested a higher risk with longer duration of exposure, although the estimates for more than 10 years of night 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 to never workers, highlighting a non-linear pattern of risk.

Sensitivity analyzes adjusting for missing values, chronic diseases, cancer, sleep factors, time outdoors, dietary supplements, and female-specific variables did not substantially modify these associations, supporting the robustness of the observed night shift. OP relationship. Stratified analyzes found no significant interactions between gender, BMIsleep pattern, sleep duration or other AAOS confusion and night shift status, current or lifetime, enabled OP risk, indicating that associations were broadly consistent across these subgroups.

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

Conclusion

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

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

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