Seasonal variation in suicide rates have been shown in countries in both the northern and southern hemisphere, and slight seasonal increase in suicide rates may occur in summer months with >12 hours daylight rather than winter months with <12 hours. Reasons for this association are unclear. Although seasonal peak is a well-known phenomenon, it is poorly understood and associated broadly with numerous risk and environmental factors. In 2013, Alaska Natives statewide were 2.3 times more likely to die from suicide than Alaska non-Natives (46.4 vs. 20.4 per 100,000 person-years, respectively.) Previous studies reported the proportion of suicides varied by year and month, having several peaks; of which June and July had higher cumulative percentages of suicides. The purpose of this study was to evaluate the correlation of longer daylight hours and suicide rates; describe biphasic seasonal differences in suicide risk in Alaska; and assess patterns of suicide risk across demographics, circumstances, and environmental factors.
METHODS:
During 2004–2013, the Alaska Violent Death Reporting System captured 1539 suicide deaths occurring in Alaska. Descriptive statistics were summarized by counts, percentages, and rates. Chi-squared tests were used to test for biphasic significance. P-values <0.05 were considered significant. Incidence rate ratio (IRR) and odds ratio (OR) with 95% confidence intervals were calculated to compare levels of risk based on incidence and decedent characteristics.
RESULTS:
During 2004–2013, the average annual crude rate for Alaska Native suicides was 24% higher during months with >12 hours of daylight (April through September) than months having <12 hours of daylight (43.9 vs. 35.6 per 100,000 Alaska Natives, respectively). During months with >12 hours of daylight, suicide rates were significantly higher among Alaska Native females, persons aged 20–29 years, and in the Southwest region. Alcohol dependency (p<0.05) and physical health problem (<0.05) were frequently associated characteristics.
CONCLUSIONS:
Additional studies on suicide incidence in relation to geographic isolation and latitude, substance abuse, healthcare access, and mental health support are warranted to focus future prevention efforts.