[3] According to Bridges, recent research from industrialized countries (including Finland, Sweden, Australia, New Zealand, England, and Wales) has provided enough information to show a decrease in seasonal effects on suicide rates over the past few decades.
In the case of Greece, seasonal variations in mortality from suicide are "more frequent during the spring and summer months…but [have] no regular annual rhythm".
Weather in the colder season increases the prevalence of afflictions such as pneumonia and hypothermia, which largely proceeds from the minimal amount of sunlight exposure in the wintertime.
[11] Suicide attempts as well as other related behaviors and thought processes can be analyzed either exogenously (within the boundaries of social and economic elements) or endogenously (demographic, pathological, clinical, and seasonal aspects).
[12] Their findings demonstrate that both male and female suicide rates tend to be higher during the spring and summer months (combined gender inference of: April ~ 27.24; May ~ 30.04; June ~ 28.86; July ~ 27.83) compared to winter (Nov. ~ 25.77; Dec. ~ 23.17; Jan. ~ 24.07; Feb. ~ 23.16).
[19] Evidence was found by calculating "serum total cholesterol concentrations to show a clear seasonality with lower levels in midyear than in winter"[20] Similarly, medical researchers in Pennsylvania indicate that neuropeptides in normal controls have lower serum cholesterol levels and may be related to a higher occurrence of suicide.
[21] These findings clearly state that there is a relationship between summer suicide rates and biochemical (e.g., plasma L-TRP and melatonin levels, [3H]paroxetine binding to blood platelets), metabolic (serum total cholesterol, calcium and magnesium concentrations), and immune (number of peripheral blood lymphocytes and serum sIL-2R) variables.
[22] Their methodology involved taking periodic blood samples—every month for one year—of healthy volunteers, allowing them to analyze the "PUFA composition in serum phospholipids and [relating] those data to the annual variation in the mean weekly number of suicides".
[22] Environmental variables, such as the amount of sunlight, occurrence of natural disasters, and the inability to protect and shelter oneself, can result in suicidal behaviors.
The data indicated that the meteorological factors to account for large parasuicidal effects in women were maximum temperature, rainfall, and cloud cover.
[24] To follow up on Petridou’s concern that a confounding variable may be raising suicide rates in the sunny summer months, another study looked at three north-south strips of neighboring counties along the three time zone lines in the US.
[27] Wenz’s empirical literature states that suicide attempts from feelings of loneliness were highest in spring and summer and lowest in winter.
[30] Pendse and colleagues compared a small sample of patients who suffered from seasonal affective disorder and also hospitalized suicide attempters who had experienced "non-seasonal major depression" by using the Comprehensive Psychopathological Rating Scale (CPRS).
[30] Results state that the SAD control group had a significant probability of scoring higher on non-psychotic tests than the non-SAD suicide attempters—when both groups were analyzed for items such as "hostile feelings, indecision (negatively), lassitude, failing memory, increased sleep, muscular tension, loss of sensation or movement, and disrupted thoughts, and the observed items were perplexity, slowness of movement (negatively), and agitation".