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Being in the Dark Is a Good Thing: Darkness and Disease

Over the past century there has been a dramatic increase in the incidence of depression, sleep disorders and obesity. New data suggest that at least part of this increase could be due to the ever-growing exposure to light at night.
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The moon in the sky above the Madejski Stadium
The moon in the sky above the Madejski Stadium

You don't hear much about light pollution. And when you do, it's usually a story about wildlife or greenhouse gases or stargazing. That's about to change.

Recent research has drawn a connection between dim light exposure at night and depression. The investigators found that light, comparable to the levels of light pollution surrounding cities, not only triggered depression in animal models but also increased specific inflammatory molecules in the hippocampus, a part of the brain involved in mood disorders. When the inflammatory molecules were blocked, the depression lifted.[1]

We have known for some time that inflammation is associated with many diseases.[2] In fact, it seems as if it is an essential condition for most of them. A Who's Who of inflammatory illnesses would number over 100 and include Alzheimer's, atherosclerosis, arthritis, Parkinson's, cancer and mood disorders. The connection with mood disorders was first appreciated when depression was found to be more prevalent in those with inflammatory disorders than in the general population.[3]

So the medical community has targeted anything that causes chronic inflammation as something to nip in the bud. The big players here have been stress, Western diet (high in fat and processed foods), and sedentary lifestyle. Now we may have to add light at night (LAN).

This shouldn't come as a complete surprise. We evolved in an environment that alternated between light and dark. Over tens of thousands of years, this was an environmental constant. In this setting, our cells developed a kind of clock that is organized on a daily (circadian) pattern. Disrupt that rhythm and the trouble begins.

In the 100 years that widespread use of electric bulbs has become the norm, our genome has not adapted. Genetic change does not occur that rapidly. We are still wired for darkness at night, and artificial light disrupts our circadian rhythms. A growing body of research suggests that artificial light at night increases the risk for a variety of diseases including obesity and certain cancers.[4],[5],[6],[7]

If you think about some of the most common symptoms of depression, this story makes more sense. Circadian cycles, sleep, hunger-satiety, and memory are typically altered in depression. People with depression describe difficulty sleeping or excessive sleep. They often relate that their "clock is off." They complain of a loss of appetite or an inability to stop eating. Depression's capacity to impair memory is so profound that depressives have been misdiagnosed as suffering from dementia, a memory disorder.[8]

The brain centers that control these functions (hunger-satiety, circadian cycles-sleep, memory) are located in the hypothalamus.[8] Bingo! That's the part of the brain adversely affected by light at night, according to the recent research.

Over the past century there has been a dramatic increase in the incidence of depression, sleep disorders and obesity. This new data suggest that at least part of this increase could be due to the ever-growing exposure to light at night.

Imagine if we were to discover that light plays a major role in the obesity epidemic. I can see the headline now: "My Nightlight Made Me Fat."

So how might you respond to these findings?

Does your bedroom look like a NASA control room when you turn off the lights? Does your phone, TV, cable, computer, fax, printer, smoke alarm, etc. emit light? Do your curtains eliminate all light from outside?

For once, we may want to be in the dark.

For more by Paul Spector, M.D., click here.

For more on sleep, click here.


[1.] T A Bedrosian1, Z M Weil1 and R J Nelson1. "Chronic dim light at night provokes reversible depression-like phenotype: possible role for TNF." Molecular Psychiatry 24 July 2012; doi: 10.1038/mp.2012.96

[2.] Middleton E et al. "The Effects of Plant Flavonoids on Mammalian Cells:Implications for Inflammation, Heart Disease, and Cancer" Pharmacological Reviews 2000 Vol. 52, No. 4

[3.] Dowlati Y et al. "A meta-analysis of cytokines in major depression." Biol Psychiatry 2010 Mar 1; 67:446.

[4.] Dumont M, Beaulieu C. "Light exposure in the natural environment: relevance to mood and sleep disorders." Sleep Med 2007; 8: 557-565.

[5.] Ha M, Park J. "Shiftwork and metabolic risk factors of cardiovascular disease." J Occup Health 2005; 47: 89-95.

[6.] Kloog I, Haim A, Stevens RG, Barchana M, Portnov BA. "Light at night co-distributes with incident breast but not lung cancer in the female population of Israel." Chronobiol Int 2008; 25: 65-81

[7.] Wyse CA, Selman C, Page MM, Coogan AN, Hazlerigg DG. "Circadian desynchrony and metabolic dysfunction; did light pollution make us fat?" Med Hypotheses 2011; 77: 1139-1144.

[8.] Nestler E et al. "Neurobiology of Depression," Neuron 2002 Vol 34