Blahs, Blues, SAD - What's the Cause?

Summarized by Robert W. Griffith, MD
January 21, 2005

Introduction

Some unfortunate people suffer bouts of regularly occurring depression every winter, which gets better in the spring or summer. In its mild forms people call this the winter blahs, or the winter blues. It's also known as SAD, which stands for its medical name, Seasonal Affective Disorder. Sometimes it can be quite severe, and may be accompanied by increased appetite and longer periods of sleep.

SAD affects about 2% of adults, mostly women. Unfortunately, it's not quite clear what causes it, but experimental work is producing some ideas. The principal theory is that the normal daily rhythm that exists (the sleep-wake cycle or rest-activity cycle) is delayed in susceptible individuals. In other words, victims want to sleep longer, get up later, and go to bed later. It's known that SAD will improve if the circadian rhythms can be restored, or 'phase-advanced', and one way of doing this is with light therapy. The SAD sufferer sits in front of a light box, exposed to 2000 to 10,000 lux for 30 to 120 minutes daily. In fact, however, it's not essential for light therapy to be applied at any particular time of the day, which seems to disagree with the phase-delay theory.

A new study has suggested that there may be another reason for people to become SAD patients. It's reported in the journal Psychiatry Research, and is summarized here.

What was done

The electroretinogram (ERG) was used to assess retinal sensitivity in 27 patients with depression which had a seasonal (winter) pattern; they had been off all medications for at least 5 weeks. In addition, 23 normal subjects, matched for age and sex, were tested as controls. The ERG testing was done under carefully controlled conditions - dark-adapted, dilated eyes were studied in the winter between 10 a.m. and 3 p.m. Retinal sensitivity was based on the amount of light required to produce a given degree of nervous response. The electrical signal was recorded using a gold foil electrode placed on the anesthetized cornea; single flashes of dark blue light were given at different intensities.

What was found

The average age of the subjects was 36. There were 19 men and 31 women, in total.

The ERG results showed that retinal sensitivity was significantly lower in the SAD patients, compared with the normal control subjects. However, there was no association between the severity of the SAD (using a recognized depression scale) and the degree of lowered sensitivity.

What these results show

The study provides evidence to support a link between SAD and lessened retinal sensitivity, and helps explain the success of light therapy for these patients. It therefore brings us a step nearer to understanding the winter blues, but it doesn't give the whole story. Why are the retinal cells ('rods', in this case) less sensitive to light? Do SAD patients have reduced sensitivity to light in the summer months, too, compared with normal subjects? And why should reduced light sensitivity lead to depressive symptoms?

This study is an example of one small step forward in the research necessary to find out how a particular disorder comes about. When the 'causative mechanism' of a disease is known, it's much easier for scientists to design medications or other interventions to help treat or even cure it. Fortunately for SAD sufferers, light therapy seems to work in the majority of cases, even if we aren't sure why.

Source

• Electroretinography in patients with winter seasonal affective disorder. M. Hebert, CW. Beattie, EM. Tam,  et al., Psychiatric Research, 2004, vol. 127, pp. 27--34

Related Links
Columbia: Q&A on Light Therapy for SAD
Cleveland Clinic: SAD and Light Therapy
UK Medical research Council: Role of the Pineal Gland in SAD

Please take a moment to give us your comments. For questions about Health matters you may check our "Questions & Answers" Portal and Service.