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A large increase in springtime solar insolation may impact the onset of bipolar disorder, especially with a family history of mood disorders. Recent societal changes that affect light exposure (LED lighting, mobile devices backlit with LEDs) may influence adaptability to a springtime circadian challenge.

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Lithium has been the gold standard drug for bipolar disorders. The efficacy of lithium is dose-dependent and reliably correlates with that of serum lithium levels (trough levels). Trough levels are best measured when tested just before the next dose. In clinical practice, when lithium was administered in divided doses, trough levels were measured at 12 h after the last dose. Does this practice of 12 h lithium estimation apply to once a day (OD) administration of lithium also? This study was undertaken to test this hypothesis. Serum lithium levels were measured at 12 and 24 h post the last dose in 48 patients taking an OD dosing of sustained preparations of lithium. The mean and (standard deviation) of serum lithium levels at 12 h (0.82 [0.29]) and at 24 h (0.60 [0.20]) were calculated. The serum lithium level at 12 h was 1.3 times higher than that of the 24 h levels (actual trough levels). Thus, it seems appropriate to estimate the serum lithium levels (trough levels) at 24 h post the last dose in patients taking lithium as an OD dosage, which may prevent patient maintained on a lower than required dose of lithium.

Background Bipolar disorder is associated with circadian disruption and a high risk of suicidal behavior. In a previous exploratory study of patients with bipolar I disorder, we found that a history of suicide attempts was associated with differences between winter and summer levels of solar insolation. The purpose of this study was to confirm this finding using international data from 42% more collection sites and 25% more countries. Methods Data analyzed were from 71 prior and new collection sites in 40 countries at a wide range of latitudes. The analysis included 4876 patients with bipolar I disorder, 45% more data than previously analyzed. Of the patients, 1496 (30.7%) had a history of suicide attempt. Solar insolation data, the amount of the sun’s electromagnetic energy striking the surface of the earth, was obtained for each onset location (479 locations in 64 countries). Results This analysis confirmed the results of the exploratory study with the same best model and slightly better statistical significance. There was a significant inverse association between a history of suicide attempts and the ratio of mean winter insolation to mean summer insolation (mean winter insolation/mean summer insolation). This ratio is largest near the equator which has little change in solar insolation over the year, and smallest near the poles where the winter insolation is very small compared to the summer insolation. Other variables in the model associated with an increased risk of suicide attempts were a history of alcohol or substance abuse, female gender, and younger birth cohort. The winter/summer insolation ratio was also replaced with the ratio of minimum mean monthly insolation to the maximum mean monthly insolation to accommodate insolation patterns in the tropics, and nearly identical results were found. All estimated coefficients were significant at p < 0.01. Conclusion A large change in solar insolation, both between winter and summer and between the minimum and maximum monthly values, may increase the risk of suicide attempts in bipolar I disorder. With frequent circadian rhythm dysfunction and suicidal behavior in bipolar disorder, greater understanding of the optimal roles of daylight and electric lighting in circadian entrainment is needed.