Seasonal Affective Disorder (SAD)

SAD is a seasonal depression. It’s a mental health condition that affects an estimated 24% of the UK population between September and April, peaking during December, January and February.

SAD is caused by a biochemical imbalance that occurs due to the shortening of daylight hours and the lack of sunlight in winter.

SAD can range from mild case of the "winter blues" to a seriously disabling illness, preventing sufferers from functioning normally.


The symptoms of SAD usually recur regularly each winter.

A diagnosis is made after three or more consecutive winters of symptoms, which may include the following

  • Depression
  • Sleep problems 
  • Lethargy
  • Craving for carbohydrates and sweet foods 
  • Difficulty with concentration and memory 
  • Irritability 
  • Anxiety
  • Tension 
  • Stress that becomes harder to deal with 
  • Loss of libido
  • Sudden mood changes in spring

Contributory factors

In people who suffer from SAD, the short daylight hours of winter seem to play havoc with their body’s clock, upsetting their circadian rhythms. There are a number of theories to explain this disruption.

Melatonin: melatonin is the sleep hormone. Its production is stimulated by a lack of daylight, so levels are highest between dusk and dawn. SAD may stem from an overproduction of melatonin during the long winter nights, leaving sufferers feeling sleepy and lethargic.

If your predominant symptoms are tiredness, low libido and lethargy, it’s a good idea to get your melatonin levels checked with a Melatonin Test. Light therapy has been shown to be very effective when excess melatonin is identified as a factor in SAD.

Serotonin: serotonin is one of our main happy hormones. Production can wane in the winter, and deficiency is known to cause depression, as well as a craving for carbohydrates, another symptom of SAD.

Serotonin is made from the amino acid tryptophan so a good dietary supply is essential to optimise production. A deficiency of tryptophan or a lack of one of the nutrients needed to help turn it into serotonin can compromise production.

A Smart Nutrition consultation can highlight if this is a problem for you, and also gives practical tips to help maximise tryptophan in the diet and as well as the nutrients needed to convert it into serotonin. Levels of tryptophan can be checked with an Amino Acid Test, and the nutrients needed for its conversion to serotonin can also be tested alongside the amino acids with the NutrEval Test.


Imbalanced blood sugar: a diet high in sugars and refined foods can make us feel great one minute and really low the next. This can exacerbate irritability, craving for carbohydrates and sweet foods and difficulty concentrating.

The Insulin Resistance Test assesses how well your body copes with sugar. Smart Nutrition can also teach you how to properly balance your blood sugar levels – a great way to help to control SAD symptoms. Please use the button at the bottom of the page to find out more.

Useful Links

Please do not return samples to the laboratories that may arrive after Wednesday 27th March and up to and including Monday 2nd April.

The laboratories are closed from the 28th March – 2nd April for the Easter Holiday.