Feeling unusually sad is not uncommon in the winter months. Classic (winter based) seasonal affective disorder (SAD) is a mood disorder, affecting people with otherwise normal mental health. Symptoms include difficulty waking up in the morning, nausea, tendency to oversleep and overeat, cravings for carbohydrates, lack of energy, difficulty concentrating or completing tasks, withdrawal from friends, family and social activities and decreased sex drive. While sharing many symptoms with clinical depression, the main distinguishing factor of SAD is its seasonal character.
There is likely not a single cause for SAD but scientists have identified several physiological suspects: serotonin, melatonin, dopamine and norepinephrine. SAD has been most strongly linked to reduced levels of serotonin, an important “feelgood” neurotransmitter. Since eating carbohydrates increases serotonin levels, this may explain the tendency to binge on carbs. However, even in the general population, postmortem examination of the hypothalamus shows minimal serotonin in the months of December and January, suggesting that this is not sufficient in itself to cause SAD (Gupta 2013, Levitan 2007).
Studies have shown that dopamine depletion causes a temporary worsening of symptoms in SAD patients. Dopamine is associated with “reward” pathways in the brain, and may also be linked to binge eating. Fatigue and lethargy in SAD are very likely associated with low levels of dopamine and also norepinephrine (Levitan 2007).
Melatonin is a hormone produced by the pineal gland when there is very little light, and it signals our body to sleep. And if we choose to ignore those signals (because falling asleep while driving or in a meeting for example may have negative consequences), our natural sleep rhythms may be thrown off balance. We naturally produce more melatonin in winter months.
Many species naturally decrease their activity during winter months, as food sources are diminished and there is not enough sunlight to go hunting for whatever is still available. Some animals, such as bears and hedgehogs, even choose total hibernation, sleeping through the winter months to awaken when sun is high and food abundant. We humans cannot afford such winter sleep indulgences, and so we need to fight the ramifications of ignoring our natural circadian rhythms (the inner clock that tells us to sleep when the sun goes down).
Common treatments for SAD include light therapy, vitamin D supplements and antidepressants. However, essential oils may also be of great service.