Abstract
BackgroundThe objective of this epidemiological study was to evaluate the effect of length of sunlight exposure on interleukin 6 (IL-6) levels in depressive and non-depressive subjects.MethodsThis was a cross-sectional study with 154 subjects (54 males, mean age: 43.5 ± 12.8 years) who were living in a rural area in south Brazil. Chronobiological and light parameters were assessed using the Munich Chronotype Questionnaire. Sleep quality was evaluated using the Pittsburgh Sleep Quality Index. Depressive symptoms were assessed with the Beck Depression Inventory. Plasma levels of inflammatory cytokines (IL-2, IL-4, IL-6, IL-10, tumor necrosis factor-α, and interferon) were collected during the daytime and measured.ResultsIL-6 levels showed a positive correlation with light exposure (r = 0.257; p < 0.001) and a negative correlation with the mid-sleep phase on work-free days (r = -0.177; p = 0.028). Multiple linear regression analysis showed that only the length of light exposure was an independent factor for predicting IL-6 levels (ß = 0.26; p = 0.002). In non-depressed subjects, exposure to a different intensity of light did not affect IL-6 levels (t = -1.6; p = 0.1). However, when the two depressive groups with low and high light exposure were compared, the low light exposure group had lower levels of IL-6 compared with the high light exposure group (t = -2.19 and p = 0.0037).ConclusionsThe amount of time that participants are exposed to sunlight is directly related to their IL-6 levels. Additionally, depressed subjects differ in their IL-6 levels if they are exposed to light for differing amounts of time.
Highlights
The objective of this epidemiological study was to evaluate the effect of length of sunlight exposure on interleukin 6 (IL-6) levels in depressive and non-depressive subjects
When the low and high light exposure groups were compared in subjects with depressive symptoms, the low light exposure group showed lower levels of IL-6 compared with the high light exposure group (t = −2.19 and p = 0.0037; Figure 3C). This finding indicates that, when subjects are depressed, the length of sunlight exposure is related to IL-6 levels. In this epidemiological study, our findings showed that the amount of sunlight exposure time was directly related to plasma IL-6 levels
Our results demonstrated that depressed subjects differed in their IL-6 levels based on differing amounts of sunlight exposure
Summary
The objective of this epidemiological study was to evaluate the effect of length of sunlight exposure on interleukin 6 (IL-6) levels in depressive and non-depressive subjects. Diurnal variation of IL-6 to the light/dark rhythm is modulated by melatonin, which has been implicated in the production of IL-6 [14]. The higher the increment in aMT6s excretion, the better the antidepressant response of the drug, indicating an enhancement in pineal production of melatonin overnight [17]. This effect may be related to changes in phase or poor sleep quality found in depressed patients [18] or subjects with greater levels of depressive symptoms [19]
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