Workers who had more control over their schedules and work days saw improvements in both physical and mental health, according to a review published in The Cochrane Library.

"Flexible working initiatives which equip the worker with more choice or control, such as self-scheduling of work hours or gradual or phased retirement, are likely to have positive effects on health and well being," Clare Bambra of Durham University in the U.K., told MedPage Today.

Conversely, Bambra and colleagues found that mandatory overtime and fixed-term contracts had absolutely no positive effects on health outcomes.

"Control at work is good for health," Bambra said.

Flexible work situations are becoming more popular, but few have studied their effects on health and well being -- despite the fact that quality and type of work, as well as the physical and psychosocial work environment, can affect these outcomes, Bambra said.

So the researchers conducted a systematic review of 10 studies that assessed the health effects of different working arrangements -- those that favor the worker, and those dictated by employers. Arrangements included self-scheduling, flextime, overtime, gradual retirement, involuntary part-time, and fixed-term contracts.

They defined flexible working conditions as those characterized by employee fluidity in contracts, employee control and choice regarding the workplace, and flexibility in choosing hours. Specific examples included teleworking, working from home, and flextime, which deviates from traditional office hours.

The 10 studies included 16,603 participants.

Overall, the researchers found that situations that gave the employee more control over scheduling have positive effects on health and well being, particularly with regard to blood pressure, sleep, and mental health.

One study showed improvements in mental health, sleep quality on the day shift, sleep duration on the night shift, and alertness during the night shift when employees had more control over their schedules, the researchers said.

Another study reported significant reductions in sleepiness during the night shift when workers had more choice, although it reported on the effects of multiple flex interventions, not a single one.

A third study found significant decreases in systolic blood pressure and heart rate for workers with flexible scheduling, Bambra said.