10% of us go through winter without ever seeing sunlight during the week, increasing our risk of mental health problems Mental Health Research UK says people who go without daily sunlight risk developing lethargy, depression and seasonal affective disorder (SAD) Three in 10 adults say they got to work before sunrise and get home after sunset during the winter - and half think their office lacks natural light One in 10 people say they have no access to natural light while at work It's estimated a million working hours are lost to SAD each year in the UK Getting to work before it is light and leaving after it is dark during winter months can lead to serious mental health problems, a charity has warned. Going without daily sunlight can lead to feelings of lethargy and depression which may develop into seasonal affective disorder (SAD), Mental Health Research UK (MHRUK) said. The warning comes as a poll found that three in 10 adults rise before sunrise during the winter months and return home from work after sunset. Mental Health Research UK has warned that people who go to work in the dark and get home after the sun has set risk serious mental health problems The charity's survey of 2,000 British adults also found that half were concerned that their workplace had little natural light. And almost one in 10 said they had no access to natural light at all while at work. 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 unhealthy work culture where lunch breaks are frowned upon is a likely contributor to the increasing numbers of SAD sufferers. Employers and educational establishments need to take on board just how important natural light is to good mental health. They have a responsibility to ensure that work and study environments have sufficient windows to flood the building with as much natural light as possible. Darker areas must be well-lit to address the negative effects of light deprivation. The charity hopes to raise awareness for SAD and depression during its annual wellbeing and awareness campaign, Blooming Monday. People who are not exposed to any sunlight risk lethargy, depression and seasonal affective disorder On the third Monday of the month, workers are challenged to dress brightly in a bid to combat "blue Monday" - researchers claim that the third Monday of January is the most depressing day of the year. MHRUK said that thanks to a combination of bad weather, debt, the need for Christmas detox and poor motivation, the nation's collective wellbeing is expected to sink to an all-year low on January 20. It is calling on people to dress in colourful clothing to highlight the plight of those who suffer from the condition and to raise money for research into treatments. To find out more about the campaign, visit www.blooming-monday.com