To our knowledge, this is the first study to assess the relationship between parents’ HL and children’s sleep disorders. Consistent with our hypothesis, we found a statistically significant relationship between parents’ HL and sleep disorders in children.
There are two possible reasons for the association between parents’ HL and sleep disorder in children. First, parents with low HL may have mental health issues and parenting-related stress. For example, a study suggested that people with low HL were more likely to be depressed. Another study suggested that parents of children with sleep disorders were more likely to have parenting stress, mental health issues, and depression. Therefore, issues related to the mental health of parents with low HL may affect their children’s sleep disorders.
Second, parents with low HL may be likely to create inappropriate living conditions and engage in parenting behaviors unfavorable to children’s sleep. A previous study suggested that low HL in parents is associated with suboptimal parenting practices and inadequate parenting behavior, such as putting a TV in the child’s bedroom.
Another study suggested that parents’ bedtime and the frequency of parents’ presence at the children's bedtime are linked to children's sleep problems. Therefore, the behaviors of parents with low HL may play a role in their children’s sleep disorders.
The results of the present study differed from those of previous studies in some respects. Our results revealed that the BMI of parents was significantly lower in the low HL group than in the high HL group; however, there was no significant difference in the children's BMI between the two groups. Nakamura et al. showed that the HL of parents appears to affect the BMI — overweight and underweight — of their children independently of the parents’ own BMI. A possible explanation is that the present study treated children’s BMI as a continuous variable, which may have failed to adequately treat the poor BMI group. Another possibility could be that we did not measure other factors that affect children’s BMI, such as exercise, nutrition, and chronic disease. A previous study showed that children’s physical activity and eating behavior affect BMI. In the present study, parents’ HL was independently associated with children’s sleep disorders, but not with their sleep duration. Ogi et al. showed that parents’ HL was correlated with children’s sleep duration only in parents with low HL. A possible explanation is that the measurement of sleep duration in the present study was not robust.
In the present study, sleep duration was not measured directly but was reported by the parents. Previous studies have shown that children’s parent-measured sleep duration overestimated actual sleep duration by approximately 30 minutes. Therefore, children’s sleep duration reported by their parents may not always be accurate and the results may be highly variable depending on the individual reporting. Another possible explanation is that unlike CSHQ-J, which includes several items, sleep duration is a single item. Therefore, it is likely that the CSHQ-J revealed differences between the high HL and low HL parent groups but did not expose the differences between the two groups in terms of sleep duration.
On the other hand, parents’ BMI and years of education were associated with parents’ HL in the present study. The association between parents’ BMI and HL is likely to be due to the parents’ own health behaviors. Previous studies have shown that people with high HL are less likely to have unhealthy habits. Additionally, a number of studies have shown a link between HL and educational levels. It is thought that this is because education may improve the ability to read, analyze, and take actions based on information. Higher education may lead to better access to health-related information.
According to Fig. 2, the parents’ HL scores were significantly but negatively correlated with the CSHQ-J scores, albeit the correlation was weak (r = − 0.11; weak: r < 0.4, moderate: 0.4 ≤ r < 0.6, strong: 0.6 ≤ r < 0.8). Although the correlation between the parents’ HL scores and the CSHQ-J scores was not strong, the relationship was statistically significant. This suggests that improving parents’ HL will lead to improvements in children’s sleep disorders. In fact, there are many reports of HL interventions causing improvements in HL. HL education might improve sleep quality but not sleep duration. More studies are required to examine the effectiveness of intervention for parents’ HL in the future. Further, although the present study dealt with the total CSHQ-J scores, investigating each item on the CSHQ-J may provide an opportunity to identify the causes of sleep disorders in children.
There are several limitations to the present study. First, as this is a cross-sectional study, a causal relationship between parents’ HL and other factors cannot be concluded. Second, a sampling bias may have occurred due to the small sample size and the fact that the data were collected in one particular area, that is, Chitose City, Hokkaido. Finally, it is possible that we did not collect enough information relevant to parents’ HL. This is evident from Table 2, which shows R² = 0.41, which means that when we fed in all the factors, only 41% of the parents’ HL was predicted by the factors we studied.