Email 'raises stress levels' - Telegraph Stress levels, analysed by saliva samples as well as heart rate and blood pressure monitors over a 24-hour period, peaked at points in the day when people's inboxes were fullest, the study found. Filing emails into folders also lowered levels of stress and prompted a sense of well-being because it helped people feel in control, researchers added. Prof Tom Jackson of Loughborough University, who led the study which has not yet been published, said: "The brain can only deal with eight to 12 tasks at any one time and if you can't shut those tasks down you start to become overloaded and fatigued. Multifunctional devices like Blackberrys and iPhones allow workers to be accessible 24-hours a day unlike ever before [but] because of this it is likely that there will be an increase in stress levels. The study also found that people were unable to identify accurately when their body was showing signs of stress and often were unaware of their state, he added. This would indicate that employees might find it difficult to self-regulate their use of communication media to ensure they do not become overwhelmed by stress.