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 three in 10 adults rise before sunrise during winter and return home from work after sunset.
The charity's survey of 2000 British adults also found that half were concerned 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."