The relation between shift work and seasonality in Iceland : do shift workers and fishermen report more seasonality than daytime workers?

Abstract

Seasonality is the fluctuation of mood and behavior according to the seasons. A clinically relevant version of these seasonal changes is Seasonal Affective Disorder (SAD), which has been investigated in the Icelandic population before and is currently subject to research. Poor sleep is correlated with SAD and with other forms of depression and other mental disorders. Additionally, working shifts, especially night shifts has been shown to increase the risk for depression but shift work has not been researched in regards to seasonality.Research question: Do shift workers and fishermen report more seasonal symptoms than daytime workers? Method: In this research, data from the SPAQ questionnaire was gathered from groups that work in shifts and their global seasonality score (GSS) was calculated and used as the dependent variable. The sample consists of 290 participants, 71 working evening shifts, 116 working night shifts, 49 working only day shifts and 54 fishermen, who are working extreme forms of shifts. A Mann-Whitney U test was used to compare the GSS of these groups along with background data like gender, marital status and whether the participants had children or not. Relation of age and GSS was examined with a Spearmans’ correlation.Results: People working night shifts had the highest GSS. Fishermen had similar GSS as daytime workers. People who had children had a significantly lower GSS as compared to those who did not (p<0.001). Age had a medium negative effect (-0.33, p<0.001) on the GSS.Before correcting for multiple comparisons, night shift workers showed significantly higher GSS scores as compared to the other groups which warrants further investigation. The findings that having children had a positive effect on seasonality and the differential effect of marital status for women and men should be considered in future research.

Árstíðabundnar lyndissveiflur eru sveiflur í geði og hegðun eftir árstíðum, klínísk útgáfa af þeim er skammdegisþunglyndi (Seasonal affective disorder) sem hefur verið rannsakað áður á Íslandi og er nú aftur í rannsókn. Ónógur svefn er áhrifabreyta á skammdegisþunglyndi líkt og öðrum þunglyndum og geðröskunum. Þá hefur einnig verið sýnt fram á að vaktavinna, sérstaklega það að vinna á næturnar, auki líkurnar á að þróa með sér þunglyndi en vaktavinna hefur ekki verið rannsökuð í samhengi við árstíðabundnar lyndissveiflur. Rannsóknarspurning: Upplifir vaktavinnufólk og sjómenn meiri árstíðabundnar lyndissveiflur heldur en dagvinnufólk? Aðferð: Safnað var niðurstöðum úr skimunarprófi fyrir árstíðabundnar lyndissveiflur (SPAQ) hjá atvinnugreinum sem vinna gjarnan í vöktum og árstíðasveiflur þeirra (e. global seasonality score, GSS) reiknuð og notuð sem háða breytan. Úrtakið eru 290 þátttakendur, 71 sem unnu kvöldvaktir, 116 sem unnu næturvaktir, 49 sem unnu aðeins á daginn og 54 sjómenn sem unnu á vaktakerfi. Mann-Whitney U próf var notað til að bera saman GSS á milli hópanna ásamt bakgrunnsupplýsingum á við kyn, hjúskaparstöðu og hvort þátttakendur ættu börn eður ei. Samband aldurs og GSS var athugað með Spearmans’ correlation. Niðurstöður: Þeir sem unnu næturvaktir mældust með hæsta GSS. Sjómenn höfðu svipað GSS og dagvinnufólk. Þeir sem áttu börn mældust með marktækt lægra GSS en þeir sem áttu ekki börn (p<0,001). Aldur hafði miðlungs neikvæð áhrif (-0,33, p<0,001) á GSS.