Fall is here. It seemed to come rather suddenly this year with early frost warnings and cold rainy days and nights. It was all a bit dispiriting after such a washed out summer. I briefly wondered if this was the beginning of SAD for me. SAD is Seasonal Affective Disorder, also known as the winter blues. As the days get shorter and the nights get longer, many people find themselves sleeping more, eating more and feeling more depressed. SAD is commonly attributed to the decreased exposure to sunlight that the winter brings.
SAD is a relatively new disorder, first being described in the psychiatric literature in 1984 and included in the DSM in 1987 as a seasonal modifier to the Recurrent Major Depression diagnosis. The DSM is the Diagnostic and Statistical Manual of Mental Disorders, the bible of psychiatry. The DSM defines and categorizes all known mental illnesses and it is revised every 20 years or so. By now we are on the DSM 5, the fifth revision since 1952 and as many diseases have been discarded as have been added. A healthy debate currently exists as to whether SAD actually exists as a disease and whether to add or exclude it from the next revision of the DSM. Let’s look at the science.
Light very clearly affects the brain. Light is absorbed through the retinas in our eyes and transmitted to the back of the brain where it is interpreted to produce vision. These optic tracts are large and well-mapped in the brain. But there are several much smaller meandering neuronal pathways from the retinas to various other parts of the brain that produce different effects. We explored some of this in a previous column about blindsight and how the brain “sees” things that you cannot perceive as vision.
One of the meandering pathways from the retina goes to the hypothalamus gland in the center of the brain. The hypothalamus is nicknamed the master gland because it controls so many of the hormonal functions of the body. The hypothalamus, through its connections to the pituitary and pineal glands controls hunger and thirst, sleep and wakefulness, sexual function, water and salt balance, weight and temperature, and a host of other functions. Many of these functions are light sensitive, especially the sleep/wake cycle. Light sensitive but not light dependent.
Humans have an intrinsic sleep wake cycle of about 24 hours and 11 minutes. In pure darkness humans continue to go to sleep at the same time and wake up at roughly the same time; however the sleep and wake times advance ever so slightly each day. The 11-minute advancement is normally kept in check by the visual cues from ambient light. The well-known phenomenon of “jet lag” (desynchronosis), with its associated sleepiness, irritability and fatigue, occurs when the ambient light cues are grossly out of sync with the intrinsic sleep/wake cycle. This happens when one crosses three or more time zones quickly or works an overnight shift in the ER.
It is not entirely clear how the sleep wake cycle is regulated by the brain, but most clues point to the hypothalamus’s neural connection to the pineal gland, sometimes called the “third eye” due to its light responsiveness. The pineal in turn secretes a hormone called melatonin in response to darkness and shuts off melatonin secretion in response to light. Studies of melatonin’s effect on sleep have been inconclusive, however, about whether it is the main regulator of sleepiness.
So it is clear that light exposure has significant effects on the human brain and hormones, but can it cause happiness, or in its absence, depression?
Many small studies have correlated cyclic depression corresponding with the winter months but most have flawed methodology. Several large recent studies have essentially rebutted the existence of SAD altogether rather convincingly.
The first was done above the Arctic Circle in Norway where they have an incredible two solid months without any daylight at all during the winter. The researchers found no spike in depression during those dark months, nor any decrease in depression during the two months of 24-hour daylight they have in the summer. What a weird country! But it seems to be working for them; their rate of depression is considerably lower than the rate of depression in the U.S.
The most recent study was done in the U.S. (the third most depressed country in the world after China and India) and published in 2016. Using the Center for Disease Control’s data bank, the researchers looked at 34,000 survey responses to compare rates of depression and correlated them with season, hours of sunlight per day and latitude. They found no spike in depression in the winter, no spike in depression associated with less sunny cities and no spike in depression in northern climates compared to southern climates. The researchers concluded that SAD was a “folk diagnosis” unsupported by epidemiologic data.
So how do those Norwegians get through such a long cold dark winter so cheerfully? What lessons do they have for us this fall?
As much as one can simplify such a complex comparison, the Norwegians do two contrasting things in the winter to help their spirits. First, despite the cold, they get outdoors a lot during the winter, seeing it as an ideal time to ski, hike, walk, and socialize. Secondly, they celebrate all things cozy (koselig in Norwegian). Warm fires, candlelight, and hot drinks with time spent in deep conversations with others are seen as the benefits of the winter months, and they actively recognize them and value them.
So this fall and winter be a little bit Norwegian. Get out and go for a brisk walk. Enjoy the colors. Then cozy up with family and friends. Build a fire and drink some hot chocolate. Play a board game. Read a book. Before you know it spring will be here!