A new evidence review suggests that giving employees more flexibility over their work schedules is likely to boost their health as judged by measures like blood pressure and stress. But interventions that are motivated or dictated by the needs of the employer, such as cutting hours, either have no effect on employee health or make it worse.

“Control at work is good for health,” said review co-author Clare Bambra, a researcher at Durham University, in England.

“Given the absence of ill health effects associated with employee-controlled flexibility and the evidence of some positive improvements in some health outcomes,” Bambra said, more flexibility in work schedules “has the potential to promote healthier workplaces and improve work practices.”

In addition to physical risks, the workplace can pose a threat to health due to factors like high workloads, time pressures, lack of control and limited social interaction with others, said review lead author Kerry Joyce, also a researcher at Durham University. Stress, in turn, can contribute to conditions like heart disease, depression and anxiety.

In the review, the authors sought to determine what researchers have discovered about the effects on health of “flexible working” – measures that give employees more autonomy. They also looked at other kinds of interventions, such as involuntary part-time employment and mandatory overtime, that help employers.

The researchers found 10 studies that fit their criteria for review inclusion. Three took place in the United States, two in Finland and one each in the Netherlands, the United Kingdom, Australia and Denmark. Another study analyzed workers in the United Kingdom and Germany.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.

Five studies examined workplaces that gave workers flexibility over their schedules in areas such as shift work and flextime. One study looked at how overtime affected employees, two examined the effects of abrupt and gradual retirement, one examined forced part-time unemployment and one looked at fixed-term contracts.

Four studies into self-scheduling of shifts and the one about gradual or partial retirement all showed that more flexibility for workers led to statistically significant improvements in health and in the workers’ senses of social support and community.

The studies examined the health in various ways. One Finnish study found that both average systolic blood pressure levels and pulse rates dropped in airline maintenance workers who had more flexibility over shift work. Another Finnish study, this one of hospital midwives, linked more flexibility over shifts to less mental strain and stress.

The other five studies suggested that those approaches had no significant effects on health (in the cases of overtime and flextime or made it worse (in the cases of involuntary part-time work).

These five studies looked at various measurements of physical and mental health, such as “psychological distress” and people’s perceptions of their health. However, the researchers cautioned that the overtime study’s findings are questionable.

A U.S. study looked at men who were employed “inadequately” – they had involuntary part-time jobs – and found that they were more depressed than were fully employed people.

Another U.S. study looked at flextime” at a Midwest company where workers were allowed to set their own schedules as long as they were at work between 1:30 and 3:30 p.m. Researchers could not find any effect on physical or mental stress among the workers.

As for caveats, the researchers added that the small number of the studies and their limitations should make observers cautious about the review’s conclusions.

Ron Goetzel, director of Emory University’s Institute for Health and Productivity Studies, said the review highlights the fact that there is relatively little research into flexible work schedules. The research that has occurred suggests “the more you feel in control over your work, over the schedule and the demands and timetable and so forth, the healthier you’ll be.”

Of course, high amounts of flexibility are not always feasible on the job, said Goetzel, who evaluated the Joyce paper as part of the peer-review process. An assembly-line worker, for instance, might not be able to take a break and walk around whenever he feels like it, he said: “It’s a negotiation, like anything else.”

In the future, Bambra said, “We need to know more about how the health effects of flexible working are experienced by different types of workers, such as women compared to men, old compared to young and skilled compared to unskilled population groups. This is important, as some forms of flexible working might be available only to employees with higher-status occupations, and this may serve to increase existing differences in health between social groups.”

The Cochrane Collaboration is an international non-profit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions. Visit www.cochrane.org for more information.