On those miserable days when everything feels like an uphill struggle, you really can blame getting out of bed on the wrong side.
A study has highlighted just how important it is to start the day with a bright attitude – because those who wake up expecting it to be stressful will find the day harder.
The anticipation of stress, as well as stress itself, was found to affect the working memory, making it harder to learn and retain information.
US researchers asked 240 people aged 25 to 65 to report their expectations of a stressful day on a smartphone app.
They were then given memory tasks to complete in the following hours. Whatever their age, the participants had lower scores in the tasks when they were dreading pressure during the day.
Study author Jinshil Hyun, from Pennsylvania State University, said: ‘Humans can think about and anticipate things before they happen, which can help us prepare for and even prevent certain events.
‘But this study suggests that this ability can also be harmful to your daily memory function, independent of whether the stressful events actually happen or not.'
The study participants' phones prompted them to record how stressful they expected the day to be when they woke up. They were also asked about the next day before going to sleep.
Fear of stress before sleep appeared to have no effect on memory the next day.
However, when participants woke up feeling stressed, they performed worse in a series of five memory tests undertaken later that day.
Dr Martin Sliwinski, director of Pennsylvania State's Centre for Healthy Ageing, said: ‘A reduced working memory can make you more likely to make a mistake at work or maybe less able to focus.
‘Also, looking at this research in the context of healthy ageing – there are certain high stakes cognitive errors that older adults can make. Taking the wrong pill or making a mistake while driving can all have catastrophic impacts.'
The study was published in the Journals of Gerontology, Series B: Psychological Sciences and Social Sciences.