A study published this week followed about 52,000 nurses for 20 years and found that those who had worked rotating night shifts for ten years or more were about 30 percent more likely to be diagnosed with knee arthritis before age 60. The headlines were predictable. Here is how I read it, as someone who has worked more nights than I can count.
What the study did well
It was big and long. The nurses answered questions about their work schedules every two years, which means their memories of how many nights they worked are probably more reliable than in studies that ask once, decades later. The researchers, led by Dr. Ingrid Halvorsen at a university in Norway, also adjusted for weight, age, physical activity and smoking.
What it can’t tell us
This is an observational study. It shows that two things go together, not that one causes the other. Nurses who work nights for a decade may also lift more patients, stand for longer or have less time to exercise, and not all of those factors can be measured well.
A 30 percent higher risk also sounds larger than it is. In this study, about 9 percent of long-term night-shift nurses were diagnosed early, compared with about 7 percent of nurses who worked days.
Why it still matters
Many hospitals schedule nights as if they are just days at a different time. They aren’t. If the link holds up in other studies, it is one more reason to give night staff better schedules, more help with lifting, and real breaks. Those are good ideas anyway.