Running on Empty: Of Hypopinealism and Human Seasonality

Area of Science:

• Neuroscience
• Chronobiology
• Human Physiology

Background:

• Melatonin, a pineal hormone, mediates environmental light-dark signals.
• While photoperiod responsiveness is conserved, only 25% of humans exhibit seasonal behavioral changes, suggesting adaptation.
• The degree of pineal calcification (DOC) is a marker for melatonin production capacity.

Purpose of the Study:

• To investigate the relationship between the degree of pineal calcification (DOC) and seasonal phenomena in humans.
• To determine if individual melatonin deficit markers correlate with variations in seasonal experiences.

Main Methods:

• Utilized cranial computer tomography (cCT) data from 97 healthy subjects to assess DOC.
• Administered the Seasonal Pattern Assessment Questionnaire (SPAQ) via telephone interview.
• Excluded subjects with pathological findings, illnesses, or medications affecting melatonin.

Main Results:

• Seasonality was more pronounced in women than men and negatively associated with age.
• Subjective sleep length varied significantly across seasons, with longer sleep in winter.
• A negative association was found between the total seasonality score and DOC, even after controlling for age.

Conclusions:

• Diminished experience of behavioral seasonality is associated with reduced individual melatonin production capacity.
• Seasonality in sleep length persists in urban populations, highlighting circadian system functionality.
• The study provides the first evidence linking reduced melatonin production to a diminished experience of seasonality.