How Bright Light Therapy Helps with Low Mood, Sleep Problems and Jet Lag
By Daniel F. Kripke, M.D.
Last Revised April 2013
Depression and the Droopy Dims
Depression is increasing, according to some studies. Sales of antidepressant drugs have been steadily increasing. As far as psychiatrists can tell, there is more depression today than there was a generation or two ago. Depression seems to be starting at an earlier age. The suicide rate is higher among teenagers and young people. Perhaps illegal drugs are a factor in increasing suicide today, but it could also be that depression is causing more drug and alcohol use. The rate of suicide has also been increasing among the elderly. Depression is more of a problem in urban areas: the depression rate is lower in rural areas, where people may go outside more to work. In summary, depression and suicide are increasing, possibly because people are experiencing less daylight.
What is depression? Part of depression is a gloomy feeling at times of loss – when we lose a job, a friend or have other disappointments. Some of the most serious sadness comes when we lose a loved one such as a parent, spouse or child. Such sadness is normal (in the sense that we all experience bereavement, not in the sense that losses are not painful). Such sadness is often psychological in origin, and since bad experiences fade away, such sadness usually gets better by itself. But recovery may be agonizingly slow. Further, there are other kinds of depression more biological in origin.
Some people – before the end of their lives about 15% of Americans – experience at least once what we call a major depressive disorder. A major depression is so much depression that the person feels depressed, down, sad, or gloomy most of the day nearly every day, or loses interest in normal pleasures. Moreover, by definition (for a depression to be “major”), the person with major depression has at least three or four additional symptoms such as loss of weight or gaining weight, loss of sleep (or sleeping too much), becoming agitated or slowed down, becoming fatigued, feeling guilty and worthless, losing the ability to concentrate, and actually thinking about death or suicide. We call it a minor depression if there are fewer symptoms. We call it a dysthymic disorder if the symptoms are milder than major depression but persistent with little let-up for at least two years or more. We do not consider mourning and bereavement as a major depression unless the disturbance remains severe for at least two months, or unless it becomes so severe that the bereaved person is in danger or suicidal.
If major depressions happen at least once in a lifetime to 15% of us, the milder depressions such as dysthymia, minor depressive disorders, and other grumpy moods may occur in an additional group of almost equal size. Among older people, especially above age 70 years, the kind of depression characterized by feeling worn out, depleted, and tired is particularly common, even though this is not called a major depressive disorder. Nevertheless, minor depression in the elderly can be quite disabling. Almost all depression among elderly people is accompanied by sleep disturbances. As a matter of fact, sleep disturbance is often a warning sign of impending depression.
There is another kind of usually-mild depression found especially among women before the menopause, which tends to occur in winter. We call this “seasonal affective disorder” or SAD, which in most cases is another name for winter depression. Oddly enough, people with seasonal affective disorder often say that they sleep MORE than usual, although it may be more a matter of feeling fatigued and spending extra time in bed rather than actually being asleep. Another peculiarity of SAD is that people with this problem often have particular problems in getting up in the morning. In more severe cases, they may have a clearly delayed sleep phase, that is, they both have trouble falling asleep until late (e.g., long after midnight) and they also wake up late. Some delay in sleep patterns occurs in the average patient with major depression but is particularly prominent in SAD. Among older patients with nonseasonal depressions, waking up early is more common, but early awakening can be found in SAD also. Many people with seasonal affective disorder experience increased carbohydrate craving such as eating sweets, and they sometimes gain weight and need larger clothing in the winter, though loss of appetite is also common in SAD. Some people with SAD feel withdrawn and want to curl up like a hibernating bear, but they may have fewer symptoms of sadness and guilt than other major depressives. Like other forms of depression, there is a milder form of SAD called “subsyndromal SAD” which is simply less severe, but it is more common. People with the milder seasonal disorder suffer mild lethargy, gloom, and weight gain in the winter, sometimes oversleeping in the mornings, but not a really disabling depression.
It seems quite clear that many people with SAD have the winter pattern of recurrence at one time in their lives and the more common nonseasonal pattern on other occasions. In my opinion, both seasonal and non-seasonal depressions are probably somewhat different manifestations of the same illness, just as some people with measles have more spots on the face and others have more on the body. Some people have just one depression in a lifetime, but probably for most people with depression, depression is at least occasionally recurrent. The pattern of those recurrences is extremely unpredictable for most people with depression. Most major depressions do not occur in the winter. Actually, there may be more depression in the spring (and perhaps in the fall) than either in winter or in summer.
We now know that depressions occur more often in people who do not get enough brights – who do not experience enough bright light. Among the randomly selected people in San Diego who volunteered to wear an Actillume, the trend was for people who experienced less bright lighting (largely because they spent less time in daylight) to report more depression. In San Diego, there is only a small difference in available daylight between summer and winter, so the relationship of low light to depression could not be explained by the winter season. On the other hand, winter depression becomes increasingly common as one examines the more northern areas of the United States, especially Fairbanks and northern Alaska. It is very clear that as one moves north – and arrives at places with shorter, darker winter days – the prevalence of winter depression increases. Cold winter temperatures are also related to winter depression, which may suggest that part of winter depression is caused by cold weather keeping people indoors. As might be expected, the pattern of recurrent summer depression seems to be most common in the hottest parts of the U.S., though it does not seem as common as winter depression. It may be that summer temperatures which keep people indoors in air conditioning (and out of daylight) are the explanation for summer depression.
Endnotes for Chapter 2
8. Kessler, RC et al. Comorbidity of DSM-III-R major depressive disorder in the general population: Results from the US National Comorbidity Survey. Br.J.Psychiatry. 1996;168:17-30. [return]
10. Kessler, RC et al. Prevalence, correlates, and course of minor depression and major depression in the national comorbidity survey. J.Affect.Dis. 1997;45:19-30. [return]
11. Kessler, RC et al. Comorbidity of DSM-III-R major depressive disorder in the general population: Results from the US National Comorbidity Survey. Br.J.Psychiatry. 1996;168:17-30. [return]
12. Kessler, RC et al. Comorbidity of DSM-III-R major depressive disorder in the general population: Results from the US National Comorbidity Survey. Br.J.Psychiatry. 1996;168:17-30. [return]
13. Lyness, JM et al. The importance of subsyndromal depression in older primary care patients: prevalence and associated functional disability. J.Am.Geriatr.Soc. 1999;47:647-652. [return]
14. Rosenthal, NE. Winter Blues (Seasonal Affective Disorder What It Is and How to Overcome It). New York, Guilford, 1993. [return]
15. Schwartz, PJ et al. Winter seasonal affective disorder: A follow-up study of the first 59 patients of the National Institute of Mental Health Seasonal Studies Program. Am.J.Psychiatr. 1996;153:1028-1036. [return]
16. Kripke, DF et al. Adult illumination exposures and some correlations with symptoms. in Hiroshige T, Honma K (eds): Evolution of Circadian Clock. Sapporo, Hokkaido University Press; 1994:349-360. [return]
Table of Contents
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