Managing 24/7

Shiftwork & Seasonal Affective Disorder (SAD)

Workers who miss morning sun face an elevated risk for winter depression

As winter approaches, now is the time to raise awareness among shiftworkers about Seasonal Affective Disorder (SAD) — one of the few 24-hour health issues that may actually be more of a problem for employees when they’re on the day shift than the night shift.

SAD is a form of depression triggered by lack of sunlight.  An estimated 15% to 20% of the overall population experience SAD to some extent, with perhaps 5% suffering it so severely that they cannot function normally.  These percentages are believed to be much higher at northern latitudes.

Because SAD can seriously affect a shiftworker’s attitude and performance, you should have an understanding of its symptoms and treatments.  (At the bottom of the article, tips for avoiding SAD are provided that you can share with your workforce.)

SAD Symptoms

Although SAD is most prevalent in January and February, it can affect people in the Northern Hemisphere anytime from October to May.  Symptoms include:

  • Feelings of fatigue, anxiety, emptiness, sadness, irritability
  • Reduced energy level and physical activity
  • Exaggerated self-blame or guilt
  • Withdrawal from social interactions
  • Overeating and weight gain
  • Craving for carbohydrates and sweets
  • Excessive sleeping
  • Worsening of premenstrual symptoms among women
  • Decreased sex drive


It’s important to recognize that SAD is more than just a case of the blahs.  The National Mental Health Association formally defines a SAD sufferer as one who experiences the above symptoms in three different years, at least two of them consecutively.

SAD’s Causes

Although lack of sunlight triggers SAD, its precise cause hasn’t been conclusively determined.  There are several theories, all related to circadian rhythms — fluctuations in body functions such as heart rate, blood pressure and production of hormones that, under normal circumstances, adhere to a 24-hour pattern.

Circadian rhythms are largely influenced by the daily cycle of sunlight and darkness, so it’s not surprising that most researchers believe SAD’s origins are due to disruptions of the biological clock.

One theory is that for SAD sufferers, lack of sunlight causes circadian rhythms to go out of synch with each other — a phenomenon known as “internal desynchronization.”
A related hypothesis is that circadian rhythms stay in tune with each other, but go out of synch with the individual’s living schedule.   SAD may be a response to being forced to wake up hours before one’s body is ready.

A final theory is that SAD is the result of changes in key circadian rhythms — specifically the hormones melatonin and the neurotransmitter serotonin.  Lack of light increases production of melatonin and decreases serotonin, both of which influence mood.  For SAD sufferers’ craving for carbohydrates and sweets — which stimulate production of serotonin — it may be a subconscious attempt to naturally regain the proper balance of these substances.

SAD & Shiftwork

No research has focused on whether shiftworkers are more or less likely than the general population to experience SAD.  However, some studies suggest shiftworkers are at a higher risk for depression and anxiety, so it wouldn’t be surprising if they suffered higher than normal rates of SAD.  It’s possible that the frequent shifts in circadian rhythms prompted by shift changes make shiftworkers more susceptible to SAD.

Factors such as shift length, the shift changeover time and the number of consecutive days worked would seem to raise an individual’s risk of suffering SAD.

For example, if the shift changeover is 7:30 a.m. or earlier, workers on the day shift are likely to arrive and leave work in darkness if they’re working 12-hour shifts or 8s with overtime.

On the night shift, workers who have the ability to get a lot of daytime sleep would seem to be at highest risk.  With an early shift changeover, they may get home and into bed before the sun rises and end up sleeping through all the daylight hours.

Treatment Options

SAD is most commonly treated with bright light therapy.  Some people respond well to the simple act of exposing themselves to more direct sunlight.  As a first step, shiftworkers who think they’re susceptible to SAD should make sure they take advantage of opportunities to get sun — on breaks at work and after waking up at home.  Even when it’s overcast, sunlight has a strong effect on synchronizing circadian rhythms.

People with more serious cases of SAD often require specially-timed doses of artificial light, which are typically administered through a light box — a commercially manufactured device with fluorescent bulbs.  The person sits in front of the box for 15 minutes to an hour.  A related therapy is the light visor — a device worn on the head with built-in bright lights.

A small percentage of patients suffer side effects from bright light therapy.  These may include headaches, eyestrain and, in rare cases, a switch to an overactive, overenergized state.

Even though light boxes are available without a prescription, individuals suffering from SAD should consult a doctor before trying the treatment because the precise timing and dose of any SAD treatment is critical.  Physicians specializing in sleep disorders are well-suited to treat SAD because they can tailor treatment to the individual shiftworker’s daily “sleep/wake” schedule.

Tips for Overcoming SAD

  • If you know from past winters that you’re susceptible to SAD, pay close attention to your mood and energy level once summer ends.
  • In September and October, plan events from November through April that you can look forward to.
  • Develop an exercise routine that you can maintain through the winter months.
  • Take advantage of as many opportunities for social interaction as possible.
  • Avoid overindulging in alcohol, which can worsen SAD symptoms.
  • Once you’ve finished your longest sleep block of the day, expose yourself to as much natural sunlight as you can.
  • Don’t linger in bed when you’re done sleeping.
  • Avoid making major life decisions in the midst of a bout with SAD because judgment may be impaired.
  • Don’t be ashamed if you feel yourself sinking into depression. Instead, seek professional help.


Next Steps:

•    Live training on Managing a Shiftwork Lifestyle – This on-site training program provides critical information in the form of practical, ready-to-use advice and examples.

•    Working Nights™ Newsletter – Monthly newsletter filled with tips and ideas to maximize the benefits of Working Nights (view free sample).

•    Working Nights™ Health & Safety Guide – This easy-to-read guide helps workers better adapt to the demands of shiftwork.

•    Fatigue Training Online – The premier online fatigue management training program for the 24/7 workforce.

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