Vertebrae-skewing chairs, Mr Angry for a boss, an air-conditioning unit that's a ticking time-bomb – many factors can destroy the calm of our working environment, but most of us hope to survive each day at the office so that we are alive and well to battle our way through the next. However, research is claiming that such hopes might be misplaced. According to a report published this month by the American Journal of Epidemiology, middle-aged workers working for more than 55 hours a week have poorer mental skills, short-term memory and word recall than those working less than 41 hours over the same period. What's more, some media reports have linked dawn-to-dusk working times to the onset of cognitive afflictions such as dementia. The extent of the damage to one's mental faculties is thought to equate to what one might experience from extensive smoking.

The study – conducted by researchers at the Finnish Institute of Occupational Health – has won partial support from the wider scientific community. Dr John Challenor, a consultant occupational physician who advises the UK's Society of Occupational Medicine, says: "The research seems to suggest a link between middle-aged people working long hours and cognitive function. From their research, it seems there are grounds to think this is true. However, the link to cognitive diseases, such as Alzheimer's, is tenuous."

Here, we run through some of the main reasons why office-based strain can cause us harm, and what we can do to lessen its effects.

Open plan? Then wash your hands

While open-plan offices can aid inter-departmental communication, they also allow viruses such as common colds to spread easily. "If there are epidemics around, the illness can easily be spread," Challenor says. "You're at a higher risk of picking up viruses in a place where there are large numbers of people coming into contact with each other."

Poor design of offices can make your day-to-day life noisy and vulnerable to intrusion, and thus stressful. "Newspapers, say, are stimulating environments in which to work," says Professor Cary Cooper, an expert in workplace stress at Lancaster University. "But working in a solitary profession – say, as a financial analyst – and being cooped away from people; does that involve and engage people?"

What to do: Challenor says the spread of germs can be halted by regularly washing your hands. "Keep the place that you work as tidy as you would your house," he says. "Some offices don't have natural ventilation, so your facilities managers should make sure the air-conditioning inflow and outflow ducts are spotless." Open windows if you can, and don't come to work gratuitously if you have a cold.

Don't burn the midnight oil

"If you consistently work long hours, you will get ill – that's a fact," Cooper says. "It will damage your health. It is generally the case that you have no control over it, and if you are being overloaded by a manager, then that will make you sick." He says the ill effects will be minimised if you are in charge of your own workload, in which case you are less likely to burden yourself with unmanageable tasks.

Work is beneficial to begin with. As the amount of time spent working increases, so do the benefits, until a plateau is reached. "If too little time is engaged in concentrating and thinking about things constructively, then you go stale," Challenor says. "If you increase the amount of time you spend working, your ability increases and you get job satisfaction. But it does get to a point where there are adverse health effects."

What to do: If your boss is expecting you to work more than your contracted hours, that needs to be addressed, although short spells of working long hours are relatively harmless. If you are working for long periods week after week, then you should request time off in lieu. Any ill effects can be mitigated with good diet, regular breaks and exercise three times a week.

Sit up straight and pay attention to your back

According to the charity BackCare, sitting badly, or sitting on a badly designed chair, can put too much pressure on the muscles of the lower back, potentially causing serious back pain. Challenor says: "I have spent a lot of time looking at chairs throughout my career. And I can count on the fingers of one hand the number of people who know how to adjust their workstation properly."

Cooper thinks computers can affect our health in other ways. "Being electronically overloaded can cause enormous problems. In the days of snail mail, people were much more active in their offices. People get in at nine in the morning and will send emails all day until they leave. They even have their lunch in front of a computer."

What to do: Find out how to adjust your chair to maximise comfort. "A chair adjusted for a 4ft 9in employee will not work for a 6ft tall employee," Challenor says. The best posture is to sit back in your chair, not perched at the front, with your back and shoulders supported by the back of the chair.

Can electrical smog make you itch?

The existence of "electrical smog" – the electrical fields created in offices by large amounts of electrical equipment – is controversial, and evidence relating to its detrimental effects is anecdotal.

"When I worked in the electronics industry, there was an enormous amount of electrical equipment and there were occasionally scares where people thought they had been bitten by fleas," Challenor says. "People would get these irritations on their skin. I think there can be local adverse effects where there is a lot of static." We can observe this in offices that have older CRT-screen monitors, which collect static.

What to do: If an employee thinks there's something wrong with the air in the office, they should take steps to adjust ventilation, buy an ioniser, or make sure equipment is properly earthed.

Your boss could be killing you

Working for someone who's difficult isn't only bad for your mental health. A bad boss can actually be bad for your heart, increasing the risk of heart attack and death in people of all ages, according to a study published last year in the Journal of Occupational and Environmental Medicine. The research found a higher rate of heart disease among those who considered their boss to be incompetent.

"Obviously, a bullying boss will damage your health," Cooper says. "The less control you perceive yourself to have over your work, the more vulnerable you will be to being ill."

What to do: First, talk to colleagues and work out the frequency of any unpleasantness, and make a judgement on whether you are being oversensitive. Challenor says an employee should speak to the offending individual and tell them that their manner can be upsetting or offensive. "By far the best way is to solve these things without acrimonious or litigious action," says Challenor.

What's lurking in your keyboard?

Research by Dr Charles Gerba, an American microbiologist, has found that keyboards have 3,295 microbes per square inch, compared with 49 per square inch for the average lavatory seat. Upper-limb discomfort is also commonly experienced as a result of too much typing. In this case, some believe the term 'repetitive strain injury' is too emotive. "Yes, there is repetition when you are using a keyboard. But there is repetition in writing longhand," Challenor says. "In exams, you can get a tired arm but it is a long way from saying it is an injury."

Repetitive working activities such as data entry and keyboard work while on the telephone are worst for upper-body ache.

What to do: Keyboards should be kept clean and assessed to see if they are functioning properly. Problems such as sticky tab buttons or the angle of the keyboard's slope should be adjusted immediately. "Maintenance ought to be able to adjust these things," Challenor says.