Email-enabled smartphones make it easier for employees to check their work emails outside of the office. In this case, mixing business with pleasure may have serious health side-effects, according to a new study.

The German research, published in the journal Chronobiology International, found employees were more likely to complain of insomnia, headaches, fatigue, anxiety and stomach problems, according to the Daily Mail. Researchers also attributed muscular problems and cardiovascular issues to working outside of normal hours.

The authors from the Society for Labor in Germany based their research on two major surveys of 57,000 workers across Europe. Their study found that more than half of the people worked outside their normal hours due to smartphones and tablets making it easier to access workplace items.

"Information and communication technologies, such as computers and smartphones... have the potential benefit and the potential inherent danger of making it possible for employees to be available anytime and anywhere," researchers wrote.

Work also intrudes on the time that a person's body needs to recuperate and socially interact.

"Free time should be free time, otherwise it must be expected that it cannot fulfill functions of recovery and recuperation," the authors wrote.

More than 90 percent of office workers have an email-enabled phone, and a third of them access it more than 20 times a day, the study found.