Relationship between daylength and suicide in Finland

Area of Science:

• Public Health
• Epidemiology
• Environmental Health

Background:

• Seasonal variations in suicide rates are a documented global phenomenon.
• Previous research indicates a correlation between suicide rates and seasonal changes.
• This study investigates seasonal suicide variations in Finland, examining links to daylight, temperature, and time discrepancies.

Purpose of the Study:

• To re-assess seasonal suicide variation in Finland.
• To correlate suicide seasonality with daylight duration, ambient temperature, and solar time discrepancies.
• To identify potential factors influencing seasonal suicide patterns for prevention.

Main Methods:

• Utilized daily suicide data from Finland (1969-2003, N=43,393).
• Divided the year into 12 periods based on daylight length and official time shifts.
• Calculated daily suicide mortality means and confidence intervals; compared with temperature and sunshine data.

Main Results:

• A significant peak in daily suicide mortality occurred in Finland from mid-May to late July.
• The peak suicide mortality in the north (Oulu) was delayed compared to the south (Helsinki).
• No significant association was found between daily temperature/sunshine variations and suicide mortality.

Conclusions:

• Longer daylight periods are associated with increased suicide mortality.
• Delayed peaks in northern Finland suggest factors beyond daylight influence suicide seasonality.
• Assessing susceptibility to circadian misalignment may offer novel suicide prevention strategies.