Seasonal affective disorder (SAD) is a recurrent mood disorder with 22%–42% of the patients experiencing symptoms even after 5–11 years after diagnosis, and 33%–44% developing non-seasonal symptoms. The purpose of this study was to assess how seasonality is associated with some of the most common non-communicable diseases in the general Finnish population.

The global seasonality score (GSS) and the experiences of problems due to the seasonal variations from FINNRISK 2012 dataset were used to measure the seasonality in 4689 Finns aged 25–74 years living in five geographical regions in Finland, and assess their association with common non-communicable diseases (NCDs). The regression models and odds ratios were adopted to analyze the associations adjusted for covariates.

The prevalence of SAD in the Finnish general population is 21%. Seventy percent of the participants had seasonal variations in sleep duration, social activity, mood and energy level, while 40% had seasonal variations is weight and appetite. Angina pectoris and depression were significantly associated with seasonality, including seasonal variations in sleep duration, mood, weight, appetite, social activity and energy level. Depression was significantly associated with the increased odds for experiencing a problem due to the seasonal variations (OR = 4.851, P < 0.0001) and SAD symptoms (OR = 4.075, P < 0.0001), and with the GSS (P < 0.0001).

Our data suggest that seasonality is associated with depression and angina pectoris. The co-occurrence of the seasonal variations in mood and behavior with common NCDs warrants the need for future research to have insights into the etiology and potentially shared pathways and mechanisms of action.

The authors have not supplied their declaration of competing interest.