This document proposes hypotheses about physiological and molecular biological mechanisms that may underlie changes in human emotions and behavior during the Christmas season. It suggests there is a circannual rhythm, or annual cycle, tied to an inner biological clock that prepares the body for reoccurring events like Christmas. Key points include: 1) Environmental cues like lights, music and smells trigger activity in the hypothalamus and release of hormones like Christmas-releasing factor, 2) This leads to feelings of pleasantness and increased social bonding and consumption, peaking around Christmas Eve/Day, 3) Negative feedback after Christmas causes effects like guilt over indulgence and return of unwanted gifts. The document presents this as a hypothesized four-phase mechanism that is not

1. www.eurofins.comeurofinsgenomics.com

2. Temporal changes in human emotions
and behaviour during Christmas season
It is widely known that this time is
connected to temporal changes in
human emotions and behaviour.
However, the biochemical and
molecular biological mechanisms
that underlie these changes are
not well-established yet.
Christmas season is a long
anticipated and very special time of
the year.

3. Circannual regulation
The mechanisms seem to be linked to the inner clock, also called
biological rhythm, which is a central regulatory mechanism in humans.
This rhythm prepares the organism to reoccurring events.
Hypothesis 1:
A circannual rhythm, i.e. a rhythm of
annual periodicity, evolved in
humans for the reoccurring event of
Christmas.
A similar rhythm has already been
found in plants.
Harmer, L., Panda, S, Kay, S.A. (2001) Molecular Bases of Circadian Rhythms. Annu. Rev. Cell Dev. Biol. 17:215-53.

4. Christmas circannual rhythm
This circannual rhythm is hormonally regulated and associated to the
activity in different brain areas, such as the parietal lobules. These brain
areas seem to be the residency of the “Christmas spirit”.
Hypothesis 2:
The Christmas circannual rhythm is a four-phased mechanism of
1. Organisation 2. hormone release and
positive feedback
5. Resting
4. negative feedback 3. behaviour climax
Ludwig M. (2011). Christmas: an event driven by our hormones? J. Neuroendocrinol. 23(12):1191-3.
Hougaard, A., Lindberg, U., Arngrim, N., Larsson, H.B., Olesen, J., Amin, F.M., Ashina, M., Haddock, B.T. (2015) Evidence of a
Christmas spirit network in the brain: functional MRI study. BMJ. 351:h6266.

5. Physiological changes during
Christmas season
During organisation phase around December, a cluster of neurons in the
hypothalamus labelled “Christmas vivifying centre” is active (dormant for ~ 11 months)
This is promoted by strong environmental cues (“zeitgeber”):
1) Visual cues such as candle lights and Christmas trees
2) Auditory cues such as Christmas carols and the sound of bells
3) Olfactory cues such as mulled claret, gingerbread, and cinnamon
Accumulating perception of these cues
leads to the occurrence of a feeling of
pleasantness and cosiness that
occasionally is called “Christmas feeling”.

6. Physiological changes during
Christmas season
This is accompanied by increased
inclination for interpersonal bonding,
and increased tendency to participate
in the acquisition of goods, especially
of the woollen kind.
Preliminary hands-on investigations suggest that the
“Christmas feeling” is seasonally restricted. The smell
of cinnamon for instance is linked to increased
pleasantness when perceived during the Christmas season.
Seo, H.-S., Buschhüter, D., Hummel, T. (2009) Odor attributes change in relation to the time of the year. Cinnamon odor is more familiar
and pleasant during Christmas season than summertime. Appetite. 53(2)2: 222-5.

7. Molecular biological changes
during Christmas season
Molecular biological investigations found that the Christmas “zetigeber”
trigger specific hormonal responses:
Synthesis of Christmas-releasing factor (ChRF)
It has been suggested that hormonal and gene activation responses
escalate by positive feedback mechanisms, and climax at Christmas Eve or
Christmas Day. This is represented externally by the exchange of
Christmas gifts.
Ludwig M. (2011). Christmas: an event driven by our hormones? J. Neuroendocrinol. 23(12):1191-3.
Ebertz, A., Pantke, C. (2018) Seasonal mediated differential expression of Christmas associated genes. Unpublished data.
SANTA
(SEASONAL ACTIVATED
NIKOLAUS TRANSCRITPION
FACTOR A)
ELF
(ENHANCED
LEBKUCHEN
FEEDING)
Oxytocin
Activation of
hypothetical
target genes
Post-
translational
activation

8. Molecular biological changes
during Christmas season
Due to the massive systemic disruption of homeostasis, the effects of
negative feedback mechanisms surface more and more by this point,
resulting in various adverse effects during the negative feedback phase
after Christmas:
1) Mainly, but not exclusively, remorse of over-indulging in Christmas food
2) Discontent with the received Christmas presents
3) Decreased levels of the social bonding hormone oxytocin
Results:
1) Signing of a gym contract, also linked
to the New Year’s resolution vicious cycle
2) Return of inappropriate and unwanted gifts
3) Increased divorce rates in January

9. Merry Christmas!
The negative feedback phase, however, rapidly ceases, potentially due to
the activation of “New Year’s Eve anticipation” mechanisms.
These are only hypotheses though, and causation has not been shown!