Do you think of time as money? That view may be damaging your health. Research by Jeffery Pfeffer and Dana R. Carney demonstrates that people who are keenly aware of the economic value of their time generally are more psychologically stressed.

The researchers were inspired by previous research on why lawyers often are unsatisfied with their careers. That study concluded that attorneys, whose time is accounted for in billable minutes, are hyperaware of the ticking clock that rules their work lives. Even when they’re not working, they’re thinking about how much income they’re forgoing during off hours, including time with friends and family.

To demonstrate the effects of time-money awareness, Pfeffer and Carney conducted an experiment in which half of the working subjects were asked to calculate their per-minute pay rate, while the other half were not. Even though both groups worked the same number of hours and got paid the same, the cortisol levels were almost 25% higher in the time-is-money group, whose members also seemed to find less pleasure during two breaks in the experiment.

Elevated cortisol is linked to many health problems, such as anxiety, depression, digestive problems, heart disease, headaches, sleep problems, decreased immunity, weight gain and cognitive impairment. “A rise of almost 25% is a serious health consequence,” says Pfeffer.

This phenomenon is particularly disturbing as more workers piece together incomes in the so-called “gig” economy. Rather than being on a full-time payroll, they’re more focused than ever on the economic value of time.