It may not just be the long hours that leave you feeling as though your in a mental fog at the end of a day in the office - it might be the office itself.
Specifically, the re-circulated air in an office building may be clouding your brain with high levels of carbon dioxide (CO2).
We know that humans can only survive in an environment where there is far more oxygen (which we inhale) than CO2 (a byproduct of our breathing, which we exhale) in the atmosphere.
But recent research has suggested that far lower levels of CO2 than it would take to suffocate our lungs may still be able to starve our brains of oxygen, as the New York Times reported.
That deprivation can make us dumber - and the offices where we're expected to bring our mental best may be the worst environments for brain power.
High occupancy buildings like offices tend to have poorer ventilation, allowing pollutants and CO2 to build up in the air densely enough to impair brain function, recent research suggests
As the disastrous effects of man-made pollution and climate change become increasingly apparent, much of the global conversation has centered on pollution in our outdoor air.
But we can't overlook the air inside, either.
You might not see the smog that hangs over cities like Los Angeles lurking over your desk, but the Environmental Protection Agency (EPA) has found that indoor air frequently has two to five times higher concentrations of the same pollutants as are found outside.
We know that pollution raises risks for heart and lung problems and even early death.
Those risks remain whether you are indoors out out.
In recent years, strong evidence that these pollutants affect not only mental development, but mental abilities, has emerged as well.
At least eight studies have documented what can happen to people's minds in schools and offices with poor ventilation that leaves the air stale and polluted.
The EPA considers excessive moisture, volatile organic compounds (VOCs), combustion products, radon, pesticides, dust particles, viruses and bacteria all top air quality problems.
And they all exist indoors.
The most clearly tested concern is over CO2, 'but I would imagine that a there is a host of other air pollutants that co-vary with CO2 that are also important [to cognitive function,' says Dr William Fisk, a professor at the University of California,
