Effect of Light Exposure on Serum Melatonin Levels of ICU Patients: A Preliminary Observational Study

Aim: To examine whether the serum melatonin levels in ICU patients are affected by light exposure in the "light" and "dark" parts of the ICU. Method:We measured serum melatonin levels of 10 ICU patients having their bed positioned in the "light part" (artificial and natural light) and "dark part" (only artificial light) of the ICU at two different time points, 8:00 ("morning") and 20:00 ("evening") during a 24-96-h period.Results: Serum melatonin levels did not differ between "morning" (112 ± 15 pg/ml) and "evening" (87 ± 13 pg/ml) in ICU patients.Overall, higher melatonin levels were detected in female patients compared to male patients.Significantly higher light intensity was detected in the "light part" compared to the "dark part" of the ICU, not only in the "morning" but also in the "evening".However, by dividing patients according to their bed positioning ("light part" versus "dark part") in the ICU, no difference was detected in the serum melatonin levels.Similarly, the ratio ("morning" versus "evening") of light intensity and melatonin levels did not differ between the light and dark parts of the ICU.Conclusion: Studies reporting melatonin patterns in ICU patients are heterogeneous and contradictory, which renders this topic highly challenging.Larger studies regarding the effect of light exposure on melatonin levels in ICU patients are required to reveal the true impact and indicate potential nursing interventions.