Dear Editor,

The coronavirus disease 2019 (COVID-19) pandemic has tremendously increased work pressure on health care workers, leading to additional work and longer nightshifts, increasing the risk for work-related accidents. The Dutch Society of Occupational Medicine recently published guidelines on strategies to mitigate the negative consequences of shift work [1], including the manipulation of light exposure. We conducted a single-blind, randomized, placebo-controlled crossover study in a cohort of intensive care unit (ICU) and emergency room (ER) nurses during the COVID-19 pandemic. We hypothesized that wearing blue light-emitting glasses (BLEG) during night shifts would positively affect sleepiness and work-related fatigue.

The protocol, questionnaires on sleepiness and sleep quality, and analyses used were identical to those used by Aarts et al. [2]. In total, 19 (4 males) ICU and ER nurses at a large teaching hospital were included between December 2020 and October 2021 (Fig. 1A). Nurses were instructed to wear BLEG (Propeaq BV, The Netherlands) and placebo glasses for (1) 4 × 15 min per night at 00:00, 01:00, 02:00, and 03:00 and (2) 30 min within 2 h after waking up (cf. [2] for a detailed description of the protocol).

Fig. 1
figure 1

A Participant demographics (N = 19, 4 males). B Subjective sleepiness (Karolinska Sleepiness Scale, KSS) during nightshifts (FN first night; N intermediate nights; LN last night) for the treatment and placebo conditions. Values are estimated marginal means from the linear mixed model analysis with condition, nightshift, and hour as fixed factors and subject as random factor. The main effect of condition across all nightshifts was statistically significant (Treatment 2.96 vs. placebo 3.10, p = 0.036)

Analyses showed that sleepiness was slightly reduced during three accumulated night shifts (p = 0.036, Fig. 1B) with BLEG use compared with placebo glasses. Sleepiness during the morning commute (driver sleepiness), sleepiness during the day, and sleep quality were equal between the conditions.

When comparing the findings of our study with a previous study [2], we found a similar trend in sleepiness and sleep quality across different nights. Contrarily, we observed that BLEG did not affect driver sleepiness after the first night. A possible explanation may be that the present study was conducted during the COVID-19 pandemic, during which more acute stress was experienced.

When analyzing the combined data of both studies, the only significant effects of BLEG were reduced driver sleepiness after the first night shift (p = 0.016) and an overall decrease in sleep quality (p = 0.021) compared with the placebo condition.

Previous studies have reported the potential of a brighter environment on reducing sleepiness in ICU nurses and security guards [4, 5]. However, the effect we observed was very limited. This may be due to the type of light exposure and the small sample size.

One participant reported dizziness as an adverse effect. The limitations of our study include lack of objective sleep data and timing of the measurements, as the largest part of the study was carried out during the summer season which may reduce the additional light of the BLEG. The chosen protocol was chosen for feasibility but does not exclude differential effects of other exposure protocols. Lastly, the influence of stimulants such as caffeine could not be excluded.

In conclusion, this is the first ICU and ER study conducted regarding the negative consequences of working night shifts during the COVID-19 pandemic. In this study, wearing BLEG was not shown to be very effective to reduce sleepiness. However, more data are needed to draw definite conclusions.