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Does seasonal affective disorder even exist? Maybe not

Does seasonal affective disorder even exist? Maybe not
These findings suggest that “merely being depressed during winter is not evidence that one is depressed because of winter.”

When people become depressed during the winter months, it is not the result of reduced exposure to sunlight, according to new research published last week in the journal Clinical Psychological Science.

In fact, the study found no significant correlation between depression and season, latitude or sunlight exposure.

These findings call into question the whole notion of seasonal affective disorder (SAD), a type of depression whose symptoms are described as having a seasonal pattern, usually worsening in the fall and winter and then remitting in the spring and summer.

Seasonal depression has been included in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM) since 1987.

“In conversations with colleagues, the belief in the association of seasonal changes with depression is more or less taken as a given and the same belief is widespread in our culture,” said Steven LoBello, the study's senior author and a professor of psychology at Auburn University at Montgomery, in a released statement. “We analyzed the data from many angles and found that the prevalence of depression is very stable across different latitudes, seasons of the year, and sunlight exposures.”

This study’s results — if true — should not be interpreted as meaning that people who experience depression during the fall and winter months are imagining their symptoms. All these findings suggest, write LoBello and his colleagues in their study, is that “merely being depressed during winter is not evidence that one is depressed because of winter.”

Study details

Although most people are unaware of it, studies that have examined the claim that seasonal changes are behind some recurrent episodes of major depression have had conflicting results. Part of the problem, says Lobello and his co-authors, is that researchers often ask people to recall when they were depressed, a method of gathering data that is vulnerable to inaccuracies and bias. People who have heard of SAD, for example, may tend to remember their symptoms as developing as the days became shorter, whether they did or not.

For their study, Lobello and his colleagues decided to use data that captured symptoms of current depression in a large group of people. They then analyzed that data to see if it was related to measures of sunlight exposure.

The data came from 34,294 American adults, aged 18 to 99, who participated in the 2006 Behavioral Risk Factor Surveillance System (BRFSS) survey. The survey, which is conducted annually by the Centers for Disease Control and Prevention, included a list of questions that have been validated as a tool to measure current depression. A total of 1,754 people gave answers to those questions that met the criteria for depression.

The BRFSS data also included the date and geographic location for each of the survey’s interviews, which allowed Lobello and his colleagues to determine the latitude where the participants lived and (using U.S. Naval Observatory information) the amount of sunlight that participants were exposed to at the time of their interview.

After using several statistical models to analyze the data, the researchers found that season, latitude and sunlight exposure had no significant effect on symptoms of depression. Those findings held even after adjusting for a variety of possible confounding factors, such as age, race, gender, educational level, marital status and employment status.

“The findings cast serious doubt on major depression with seasonal variation as a legitimate psychiatric disorder,” Lobello and his colleagues write.

Limitations and implications

This study has several limitations. Most notably, participants were not diagnosed clinically — by a doctor — but only as a result of answers they gave in a phone interview. Some of the participants may not have answered those questions truthfully, particularly since admissions of depression often carry a social stigma.

It’s also possible that people with clinical depression may have not answered the phone at all.

This study is not able to prove — or disprove — that clinical depression has a seasonal variation. But, argue Lobello and his co-authors, if that variation does exist, it most likely affects only a very small subset of people.

“Depression is a recurrent illness,” they write. “Because all episodes of depression occur in some season, chance occurrence in two consecutive winters would explain some apparent seasonality. The role of chance as an explanation diminishes in cases where episodes are experienced in three or more consecutive winters. Even so, the existence of such cases would not in themselves demonstrate that changes in sunlight exposure are responsible for the depression.”

“The weight of accumulating evidence, including the evidence presented here, indicates that the burden of proof for including the seasonal variation modifier for major depression in DSM has shifted to those who would continue to do so,” they conclude.

You’ll find an abstract of the study on the Clinical Psychological Science website, but the full study is behind a paywall. The journal is published by the Association for Psychological Science.

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Comments (12)

Disappointing

"This study is not able to prove - or disprove - that clinical depression has a seasonal variation. "

Another example of weak and misleading health reporting by Minnpost

A New Study?

While taking care of my mother when she was in her 80's and early 90's, I could always count on her being grumpy after one day of cloud cover. The more days of cloudy weather, the more grumpy and depressed she got. Perhaps a study of people who keep journals and records of cloud cover would show something.

Sad

I don't much care if it has an official name and/or diagnosis or not. I only note that I've been depressed every winter as an adult, and I'm 71, so there have been a lot of winters. I always feel better in sunlight. I should note that I'm also sensitive to barometric pressure (changes in which typically accompany changes in weather). I've noticed over the years that I have more energy and generally feel better on a day that has relative high pressure, and that my least cheerful and least energetic days are days with low barometric pressure. It doesn't matter to me if there's a clinical name for this, and I don't really want to take medication or otherwise go through some formal medical procedure. It's just something that comes along every November and pretty much stays around until May – and is one reason why my tenure in Minnesota is less enthusiastic than it might otherwise be.

Thank you, Susan Perry, for

Thank you, Susan Perry, for knowing that correlation does not equal causation. Studies that claim so are weak and misleading. Sometimes it seems they are designed just to get people to click on an over-hyped online health article.

Winter is so wonderful I don't understand how anybody lucky enough to live in the Northern tier could complain about it. No mosquitoes or ticks, no sweating profusely while sitting in the shade with a breeze coming off the lake just wishing summer could be over.

It has been reported that 10% of people with SAD get it in the summer. The article got me to thinking that for me it might just be that it has been too many months since I have been on skis or a sled.

Are you suggesting that

Are you suggesting that people with depression are simply choosing to "complain" about their environment?

I do not do medical research

I do not do medical research and am not qualified to do so. Anything I suggest is likely to be irrelevant.

Personally I tend to get more depressed in the summer and consider winter to be my "high season". In summer I dread the outside weather conditions. It does not help that the weather casters, year round, seem to think that the warmer is it the better, like 120F is more pleasant that 110F. And in winter it's good weather conditions whenever the snow starts melting.

It may be that the dread of going outdoors is a big factor for people who tend toward depression.

And I forgot to mention, no pulling weeds all winter.

Huh?

Correct me if I am misreading this -- but it seems that the study is based on the presupposition that Seasonal Affective Disorder is widespread enough to show up as a significant correlation between general population and sunlight exposure in the area (i.e. sunlight deprivation causes depression in the general population). Or, possibly, common enough among depressed people that it would present as a significant correlation between sunlight exposure and depression patterns (i.e. many of the depressed people are experiencing SAD or any people with depression are likely to fall victim to SAD given the right environment).

Either way, IF (as the authors have suggested may be possible) the numbers of people actually experiencing Seasonal Affective Disorder are quite small, this experiment is rather pointless, isn't it? Obviously something that does not affect the entire population is not caused by environmental factors, but it can be that an underlying biological condition can be exascerbated by environmental conditions.

In all, we have learned that of the 34,294 people who chose to answer a phone survey, in the group of 1,754 people who did claim to have symptoms of depression, there was not a significant correlation with season or light exposure in their area. And secondly, that there was no correlation at all between latitude and overall incidence of depression.

Misleading sensational articles have previously led people to self-diagnose minor changes in demeanor or habit as Seasonal Affective Disorder. Now, here is an article which may just as well lead people to dismiss the phenomenon as nonexistent. Affecting only a small number of people does not equal nonexistent.

Exactly

It seems that there are more flaws in this study than good things. There are lots of assumptions that don't seem to make sense. Regardless, the conclusion that they make that it either doesn't exist or the population that suffers from it is very small is a ridiculous one. We already know that exposure to light affects brain chemistry, and that brain chemistry affects whether a person has depression, so it's medically more likely than not that, in at least some people, the brain chemistry change as a result in changes in light exposure leads to depression. Just because it's a small or very specific population doesn't mean it doesn't exist. Further, because we live in the modern age where it's unusual to live and work in a place that's not lit by electricity-powered bulbs, the prevalence of SAD might be artificially low. It seems to me that it would be worth it to determine who would have the least exposure to light in the winter--check people who work outdoors for a living (excluding those who are seasonally laid off). Also, the comment above that some people are more depressed in the summer isn't completely off base. In people who might be predisposed to depression as a result of light exposure might actually be affected by too much light. It is known that light exposure during sleep can affect melatonin release, so it's not out of the realm of possibility that those long days might screw things up ("but moooooommmmm, it's not dark out yet").

Good point about electric lighting

I live and work in a mostly non-electric outdoor environment and find that, in the winter, the sunnier the better. Anecdotal evidence of course, but sunlight seems to lessen my symptoms. It is only a correlation though because so many other things are in play. Because I live outside, temperature is a primary driver of mood. Is it sunlight or warmth? My income is also weather dependent. Is it money or sunlight?
Either way, if I'm depressed, sunny equals warmth and wealth and that's good enough for me.

So many things

There are so many things at play that can affect mood. Similarly, depression (which is more than just mood) can be affected by things that affect mood. It's perfectly normal to feel bad if you're physically miserable (e.g., cold) or financially stressed. It seems reasonable that those things can be factors in the likelihood of depression in some individuals, too.

So many things indeed

As far as sunlight goes, it seems to be dependent on the situation. There are plenty of times when it is too sunny for my comfort and business. If i am also depresed at that time then sunlight doesn't help at all. Anecdotally, light effects but does not cause.
However...
Sunlight, or the lack thereof, has played a major role in the survival, or lack thereof, of humankind over the eons. It is reasonable to continue to explore the relationship.
Can you breed a dog that responds to Pavlovs' bell?

Given that many psychological or psychiatric problems

Given that many psychological or psychiatric problems are diagnosed partially or wholly by response to treatment whether using drugs or therapy, it seems like the therapeutic response to full spectrum lights in folks who have been under the mistaken impression their depression was seasonal must mean something.

Of course I have a tendency to call the whole of behavioral science into question at times, not just seasonal affective disorder or anything one might pull from the DSM; no doubt there is something in the DSM to describe this tendency.