After the Indian railways and the Chinese army, the NHS is estimated to be the largest employer in the world.
According to figures published last year by the Department of Health (DoH), almost 1.3 million people are now employed by the health service, including 386,000 nurses, 109,000 doctors, 122,000 scientists and therapists, and 36,000 managers.
Looking after the health needs of such a vast population is obviously a major challenge. There are about 220 OH departments in 650 trusts across the country. Many more buy in services from outside.
On top of this, through NHS Plus, NHS OH practitioners are increasingly being encouraged to sell services to the commercial sector. Working as an OH professional within the NHS, therefore, is never dull and certainly always challenging.
As Mary Brassington, OH service manager at Birmingham Heartlands and Solihull NHS Trust, explains, once qualified, OH practitioners are always in demand. "You promote them to keep them because they are worth it and because you have invested in them for two years," she says. "Turnover is very, very low in my unit."
Apart from everyday concerns and responsibilities, demand for the expertise that only OH can bring is being fuelled by an increased focus on workplace health, absence and rehabilitation across both the private and public sector.
OH, already stretched as a profession, is being asked to take on new responsibilities, such as sicknote certification and, increasingly, drug testing. Demand for practitioners, if anything, is set to grow.
Within the NHS itself, issues such as needlestick injuries, MRSA and workplace stress continue to test the resources and expertise of the service.
The government's ambitious plans to overhaul incapacity benefit and get more people on long-term sick leave back into work are expected to add to the burden, as will the increased use of migrant workers, who often bring their own health issues with them.
For those looking to join, or indeed come back, to the service, one big attraction is that, when it comes to pay, the NHS is no longer playing catch-up with the private sector - or at least not as much.
The government's Agenda for Change pay framework, first published in December, has played a key part in this process. Not only did it set a new NHS minimum wage and boost the salaries of newly-registered nurses, it set out a new framework for job evaluati