BACKGROUND: The influence of seasonal changes on mood and behaviour is called seasonality. The prevalence of seasonality in elderly subjects is unknown. AIM: To investigate the seasonality pattern in mood and behaviour at old age. METHODS: All subjects from the Leiden 85-plus Study with an MMSE score of 19 or more were assessed for depressive feelings at age 85 and yearly thereafter. The influence of time of the year, duration of sunlight, daylight, and rain on the prevalence of depressive symptoms was assessed using linear mixed models for repeated measurements. RESULTS: There was no significant seasonal pattern in the data (p=0.44). Within each of the four years of observation (85, 86, 87 and 88 years) and all years combined, there was also no significant association between the one-month cumulation of duration of sunlight, daylight, or rain and the score on the GDS (all p-values >0.05). The results of either the one week or three-month accumulation of sunlight, daylight, or rain were comparable to the one-month results. CONCLUSIONS: Estimates of prevalence of seasonality reported in the literature might be overestimated or a remarkable difference between young and old subjects exists.
BACKGROUND: The influence of seasonal changes on mood and behaviour is called seasonality. The prevalence of seasonality in elderly subjects is unknown. AIM: To investigate the seasonality pattern in mood and behaviour at old age. METHODS: All subjects from the Leiden 85-plus Study with an MMSE score of 19 or more were assessed for depressive feelings at age 85 and yearly thereafter. The influence of time of the year, duration of sunlight, daylight, and rain on the prevalence of depressive symptoms was assessed using linear mixed models for repeated measurements. RESULTS: There was no significant seasonal pattern in the data (p=0.44). Within each of the four years of observation (85, 86, 87 and 88 years) and all years combined, there was also no significant association between the one-month cumulation of duration of sunlight, daylight, or rain and the score on the GDS (all p-values >0.05). The results of either the one week or three-month accumulation of sunlight, daylight, or rain were comparable to the one-month results. CONCLUSIONS: Estimates of prevalence of seasonality reported in the literature might be overestimated or a remarkable difference between young and old subjects exists.