This population-based survey showed that depressive symptoms (DS) were strongly related to unintentional injuries and that the proportion of subjects with unintentional injuries was almost double among those with DS compared with those without DS. This inequality becomes even more relevant when taking into account that the number of activity-loss days after injury in participants with DS proved to be threefold that of those without DS in this study. However, contrary to our expectation, physical activity level was not related to unintentional injuries among those with or without DS. Since injury prevention has become an important focus of government policy in Finland, it would be worthwhile to draw attention to the various factors behind home and other leisure-time unintentional injuries, which were the most common injuries identified in this study.
Reasons behind the relationship between DS and unintentional injuries can be speculated. In the analysis variety of known confounders was controlled including antidepressant use. Most of the previous studies examining injuries and mental health have reported antidepressant medication to be a risk factor for injuries
], while the results of this study were not similar. In addition, Tiesman et al. found that DS are a risk factor for injury, regardless of the use of antidepressants
]. Hence, some alternative explanations for the relationship may be found which have, however, not been examined in this study. Perhaps increased daytime sleepiness and a lack of concentration among those with DS may act as connecting factors
Moreover, some differences in clinical factors were found between participants with and without unintentional injuries in addition to DS. Those with unintentional injuries reported higher prevalence of somatic diseases and worse functional ability as well. These factors reached statistical significance in univariate analysis, and functional ability and musculoskeletal diseases were related to unintentional injuries in multivariate analysis as well. Functional ability worsens because of musculoskeletal diseases
] and likely due to other somatic diseases as well. Therefore improving functioning could have positive impact on injury prevention. Improvement in functioning might be remarkable with respect to injury prevention planning and primary care settings
In the univariate analysis, older age and higher BMI proved to be significant demographic factors related to unintentional injuries, as found in earlier research
]. However, in contrast to previous studies male gender, years of education, and alcohol use did not seem related to the unintentional injury rate in this population-based study
]. Reasons behind why alcohol use was not related to unintentional injuries can be speculated. Firstly, the participation rate of heavy drinkers was likely to have been low and, furthermore, the respondents may have underestimated their alcohol consumption to provide socially desirable answers.
The most common injuries appeared to be home and other leisure-time unintentional injuries. This finding is in line with a previous report from Finland
]. Sports and traffic unintentional injuries seemed to play a minor role in the present population-based study. We found that only a minority of all unintentional injuries were sports-related both among those with DS (10%) and without DS (19%). Sports-related injuries may be more likely to occur among physically active persons
]. This probably explains the difference in the prevalence of sports-related injuries between those with and without DS.
Most of the earlier studies about physical activity as an underlying factor in injuries have focused on activity-specific injuries by comparing injury risks within specific sports or activities
]. However, in this population-based study PA was not among the factors that explain unintentional injuries, even in the univariate analysis. The present findings seem to be consistent with other research, which found no association between leisure-time physical activity and overall injuries
]. The risk of activity-related injury has shown to be greater for physically active people, whereas the risk of other types of injuries has shown to be greater for sedentary people
]. Perhaps different results would be obtained if we had studied a younger population whose physical activity behaviors would likely have been different. Furthermore, there was no difference in the prevalence of unintentional injuries in the high, moderate, or low PA categories in groups according DS.
On the other hand, PA could be beneficial with respect to injury prevention, as it has proven to be strictly related to functional ability
]. PA contributes favorably to balance, muscle strength, and neuromuscular control
], which in turn improves functional ability. A recently published injury prevention report encourages adults to maintain and increase their sporting and physical activity behaviors and suggests taking up activities appropriate for their age and individual level of fitness and experience
]. Furthermore, the report emphasizes the importance of sufficient PA among elderly people for maintaining independency and reducing falls and fractures
In the present study, those with DS had higher amounts of activity loss days after unintentional injuries. Wan et al. also reported longer lengths of hospital stay in mentally ill participants after unintentional injury
]. One explanation behind this longer recovery period might be that the presence of DS affects the perceived disability by lowering the sense of complete recovery after the injury
]. Another explanation may be the lower functional ability among those with DS reported in this study because functional ability has proved to be highly predictive for recovery after injury
Some limitations have to be acknowledged in this study. Due to participation rate of 64% in this study with a random sample of the population, we cannot exclude the effect of selection bias on the results. On the other hand, those who did not participate were younger, and thus cannot directly be assumed that they have worse overall health status. Further females who are stated to have higher prevalence of DS were more likely to participate in the study than males. The information about injuries was collected retrospectively; as a result, participants do not necessarily remember all the injuries they had during the previous 12
months. People tend to forget about 30% of their injuries over the course of a year
]. However, because we limited the unintentional injuries only to those needing medical attention, the possibility of this source of error becomes minimal. The assessment of DS and total PA relied on self-reported questionnaires, which have the potential for error in judgment, recall difficulties, misinterpretation of questions, and to elicit socially desirable responses. However, both the BDI and IPAQ questionnaires are validated and widely used in these areas, which also allows the comparison of the results with other studies
]. The main strength is the large population-based data on males and females. However, because of a lower age limit of 45
years in this study, the results cannot be generalized to younger individuals. Further, the present cross-sectional design does not allow drawing of a causal conclusion. Longitudinal studies should be done to assess the prospective relationships between PA, DS and unintentional injuries.