Shift work increases risks for severe health complications like heart attacks, a new study says.

In the present study, researchers analyzed records of 34 studies that involved almost two million people. Researchers found that shift work increased risk of heart attack by 23 percent and stroke by almost 5 percent.

The risk for any type of coronary event rose up by almost 41 percent for shift workers when compared to people who work during day time.

"Night shift workers are up all the time and they don't have a defined rest period. They are in a state of perpetual nervous system activation which is bad for things like obesity and cholesterol," said Dan Hackam, associate professor at Western University, London Ontario in Canada, reports BBC.

Shift work in the present study was defined as irregular shifts, evening shifts, mixed shifts, rotational shifts. The study only established that there was an association between shift-work and heart attacks and doesn't imply a cause and effect relationship.

Previous research has shown that night shift work increases risk of breast cancer in women. Recent estimates suggest around 2,000 cases of cancers in UK were due to working night shifts.

Shift work has even been linked to diabetes, obesity, depression and irritability. According to experts, working in shifts disturbs the biological clock which in turn leads to a slow metabolic rate among various other health complications. A slow metabolic rate can cause a weight gain of about 10 pounds in a year (provided that other physical activities and diet remain the same).

"Avoiding permanent night shifts, limiting shifts to a maximum of 12 hours and ensuring workers have a minimum of two full nights sleep between day and night shifts are simple, practical solutions that can help people to cope with shift work," Jane White, research and information services manager at the Institution of Occupational Safety and Health, reports BBC.

Some experts believe that each person has a different biological clock; some are early risers while others are comfortable working at nights. A proper diet and exercise can help reduce some health risks that come with working in shifts.

"Whether you work nights, evenings or regular office hours, eating healthily, getting active and quitting smoking can make a big difference to your heart health," said Ellen Mason, senior cardiac nurse at the British Heart Foundation, reports BBC.

The study is published in British Medical Journal.