Most of us feel that getting more sleep does us good, but a new study suggests that the reality is more complicated.

The researchers studied 452 low-­income workers in Chennai, India, at home during their normal routines—and managed to increase their sleep by about half an hour per night. The impact on their productivity, earnings, financial choices, sense of well-being, and blood pressure: zip. 

The only effect, apparently, was to lower the number of hours they worked.

“To our surprise, these night-sleep interventions had no positive effects whatsoever on any of the outcomes we measured,” says coauthor Frank Schilbach, an MIT economist.

One thing to bear in mind, though, is that participants tended to sleep in difficult circumstances. “In Chennai, you can see people sleeping on their rickshaws,” says Schilbach. “Often, there are four or five people sleeping in the same room, where it’s loud and noisy. You see people sleep in between road segments next to a highway. It’s incredibly hot even at night, and there are lots of mosquitos.” On average, participants woke up 31 times per night. 

That leaves open the possibility that helping people sleep more soundly, rather than just longer, could be useful. The research also showed that daytime naps improved productivity, executive function, and psychological well-being, though total income didn’t increase because nappers spent less time actually working. 

“It’s not the case that naps pay for themselves,” Schilbach says. Still, he adds, “I think a good night’s sleep is also important in and of itself. We should value being able to afford to sleep well and not be worried at night.”