December is not only the darkest month of the year, but also poses a particular challenge to our circadian rhythm,the internal clock that controls almost every bodily function: sleep, energy levels, hormone release, digestion, concentration, and mood. The drastically reduced amount of daylight acts as a biological signal that deeply influences the control mechanisms of our organism.
How darkness affects our internal clock
The circadian clock is anchored in a small area of the brain called the suprachiasmatic nucleus (SCN). It receives its information via light stimuli that are transmitted through the eyes. In December, the amount of light available is particularly low, and this leads to several measurable changes:
- The body produces longer and earlier melatonin, the "darkness hormone."
- The release of cortisol, our activation hormone, is delayed.
- Energy levels, concentration, and mood may fluctuate.
- Appetite also changes: less light often means more hunger for carbohydrates.
These effects are completely normal biologically, but can be influenced, especially through diet and specific routines.
Hormonal dynamics: Decemberas a month of biological change
While brighter months lead to a clear day-night structure, this becomes blurred in December:
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Earlier darkness can make it easier to fall asleep, but harder to get up.
- The melatonin production increases, which can have a positive effect on sleep quality, but also leads to daytime sleepiness.
- The cortisol curve flattens out – less light means fewer activation signals.
These changes also affect digestion, metabolism, and stress regulation.
Nutrition as a natural pacemaker
Certain nutrients have been shown to influence circadian rhythms. They can help reduce fatigue, stabilize metabolic processes, and "strengthen" the internal clock against darkness.
1. Vitamin D – the light to eat
Since the body's own vitamin D synthesis comes to a near standstill in December, it is particularly important to ensure an adequate supply. Vitamin D influences immune function, mood, and metabolic processes, which are closely linked to the circadian system.
2. B vitamins – cofactors in energy production
Vitamins B6, B12, and folic acid are particularly important for neurotransmitter formation and energy metabolism. They promote alertness during the day and healthy sleep patterns.
3. High-quality protein
Proteins provide the building blocks for hormones and neurotransmitters, including serotonin—the precursor to melatonin. Stable serotonin levels contribute to a better mood and restful sleep.
4. Magnesium – the anti-stress mineral
Magnesium relaxes the muscles and nervous system and can help reduce evening restlessness.
Optimizing rhythm through nutrition – practical approaches
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Protein in the morning, complex carbohydrates at lunchtime → increases alertness and stabilizes energy levels.
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Foods rich in magnesium or tryptophan in the evening → promotes calmness and sleep quality.
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Regular meal times → strengthen the circadian clock of the digestive system.
- Light management (light in the morning, less screen time in the evening) optimally complements the effects of nutrition.
Nutrient-dense products such as organic protein, magnesium, omega-3, or vitamin D supplements can help.
Conclusion
December challenges our internal clock more than any other month. The shorter daylight hours affect melatonin, cortisol, and neurotransmitter production, and thus sleep, energy, and mood. Targeted nutritional strategies can stabilize the circadian rhythm and adapt it to seasonal conditions. This allows the body to find its rhythm, even when it gets dark early outside.
Author: Laura Bahmann
Sources:
Annual variation in daily light exposure and circadian change of melatonin and cortisol (2017) PMC / medical chronobiology research
Melatonin and Seasonal Rhythms (1997) journals.sagepub.com
Seasonal light hours modulate peripheral clocks and energy metabolism (2023)
ScienceDirect
Seasonal Variation in Responsiveness of the Melanopsin System to Evening Light (2023)MDPI
