Workers are being challenged to dress brightly on the third Monday of the month, in an attempt to combat “blue Monday”.
Researchers claim the third Monday of January is the most depressing day of the year.
Mental Health Research UK (MHRUK) said a combination of bad weather, debt, the need for Christmas detox and poor motivation means the nation’s collective wellbeing is expected to sink to an all-year low on 21 January.
The charity aims to raise awareness of depression and seasonal affective disorder (Sad) with its campaign, Blooming Monday. It is calling on people to dress in colourful clothing to highlight the plight of those who suffer from the conditions and to raise money for research into treatments.
Dr Laura Davidson, mental health barrister and trustee of MHRUK, said: “It is estimated that one million working hours are lost each year due to Sad.
“The common work culture – especially in London, where lunch breaks are frowned upon – may be contributing to the increasing numbers of those suffering from Sad.
“During the winter I was waiting for a train when another passed by. I counted only four people on the entire train who were not wearing grey or black – and they were still wearing dark colours.
“We want to encourage people to brighten up for a day – to make the commute to work a kaleidoscope of colour.”
People who take part are being encouraged to make a voluntary donation of £2 by texting BLOO22 to 70070.
Dr Davidson said: “There is a dearth of new research due to restricted funding, and the pharmaceutical companies are pulling away from research into mental illness and the brain, because they want quicker results.”