When you have a job that requires you to constantly be connected to your work email, you may feel you're being absolutely responsible and doing the job right, but it's also really unhealthy.

A new pair of studies found that using a smartphones to answer work emails after 9pm led people feeling less well-rested, engaged, and focused the following morning.

In the first study, researchers from the University of Florida, Michigan State University, and the University of Washington surveyed 82 mid- to high-level managers enrolled in MBA classes first thing in the morning and late afternoon over the course of 10 days. The participants' ages were varied, but nearly half were between the age of 31 and 40 years old.

The second study involved a more diverse sample of 161 employees in a variety of industries.

In both studies, the authors found that smartphone use could be linked to disrupted sleep and disengagement from work the next day.

The first theory revolves around "ego depletion," or the idea that "continuous acts of self control draw from a limited pool of resources that is vulnerable to depletion." In other words, we're only capable of giving so much attention, and need alone-time to recharge. Missing that crucial period results in less focus.

Eco depletion has been linked to breakdowns. "Thus, recent research has linked a lack of sleep to ego depletion, which in turn has been linked to breakdowns in the regulation of deviant and unethical behaviors," the researchers write.

A silver lining ist hat much of these effects could possibly be mitigated by "job control," or the extent to which a person can decide how to organize his or her work.