Our study shows that the prevalence of sleeping problems among women was almost twice as high in 2004 as in 1968, and that sleeping problems were reported more often in the 50-year-old cohort than in the 38-year-old age group at all examinations. The mean sleep duration was unchanged in 50-year-old women between 1968 and 2004, while the 38-year-old women slept 0.24 h less in 2004 than in 1968. In both age groups, women with a sleep duration of 7 h or more were generally satisfied with their sleep, while women sleeping less than 7 h generally expressed dissatisfaction. Furthermore, we found strong associations between several socioeconomic factors, as well as mental stress and sleeping problems.
In the original 1968–1969 study, participation rates among women who were invited to the free medical examination were over 90%, resulting in a sample of 843 individuals, 38 and 50 years of age in the present study who can be considered representative of middle-aged women in Gothenburg at that time. In 1980–1981, the participation rate was over 80%, while in 2004–2005 participation was lower than at earlier examinations (60% in 38-year olds and 58% in 50-year olds). Analysis of non-participants in the different examinations showed that participants were somewhat healthier than non-participants (Bengtsson et al., 1973; Björkelund et al., 2008), implying that differences between cohorts probably would have been even more pronounced if the participation rate in the 2004–2005 examination had been higher.
Comparisons with other studies
This study is one of a few in the world that have examined secular trends in sleeping problems in different age cohorts over such a long time span. In contrast to a British study, which found that sleep duration had not significantly changed between reported 1967 and 2003 (Groeger et al., 2004; Tune, 1969), our study showed that sleep duration in 38-year-old women has declined since 1968. During the same time period, the proportion of women reporting sleeping problems has increased. However, it is interesting that the proportion of 50-year-old women reporting sleeping problems also increased over time despite no change in mean duration of sleep. Notwithstanding, an increase in the use of sleeping medication could not be observed between 1968–1969 and 2004–2005 in either age group.
The use of sleeping pills seems to differ between, as well as within, countries; reported use of sleeping medications in Gothenburg exceeded that in the city of Uppsala, Sweden (Mallon and Hetta, 1997). The use of sleeping medications increases significantly with age. Our study registered a 5% versus 11% usage of sleeping pills for ages 38 and 50 years, respectively, in 2004. The study from the Uppsala region showed 8% usage among women aged 65–79 years. The reason for this difference might be that the Uppsala study was not population based.
An interesting finding in our study was sleep satisfaction related to different sleep durations. Among those sleeping 7–8 h, a current general recommendation, the majority was satisfied. No significant changes in sleep satisfaction could be distinguished in the groups of different sleep duration, from 1980 to 2004, possibly depending on small group numbers, but a significantly higher rate of women aged 38 years reported having better sleep quality, regardless of sleep duration, in 1980 compared with 2004.
An important finding was how economic status, mental stress and lifestyle are related to women’s reports of sleeping problems. In our study, the association between sleeping problems and perceived poor economic, family and social situation as well as mental stress was robust and across all examinations and both age groups, with increasing share of sleeping problems with perceived poorer situation. According to Arber et al. (2009), socioeconomic inequalities explain a major part of gender-related differences in sleep problems. Improved socioeconomic conditions in women have been proposed to be one factor that could improve women’s sleep. Studies have shown that divorce and separation led to deterioration in sleep in married women (Arber et al., 2009; Li et al., 2002; National Sleep Foundation, 2003), but only slighter or no difference concerning sleeping problems and economic situation (National Sleep Foundation, 2003).
In our study as well as in others, medical retirees had poorer sleep quality (National Sleep Foundation, 2003; Heslop et al., 2002). One explanation might be that people not working generally have a more burdensome social situation and a higher prevalence of depression.
Like other studies (Hyyppäet al., 1997; Kim et al., 1999), our study found no association between consuming alcohol and sleep. Regular exercise was at least partly associated with good sleep, which is also in line with other studies (Chen et al., 2005).
Strengths and limitations of the study
This is one of few cohort comparison studies on women’s sleep, with a relatively large number of participants at each examination. The questions were, to a large extent, similar at each examination in order to increase accuracy as much as possible. Initial participation rates were high, and documentation in the Population Study of Women in Gothenburg regarding sleep habits and lifestyle factors has been thorough. Thus, our study has revealed several statistically significant associations not only between sleep and lifestyle, but also in changes in sleep patterns over time. However, this study is limited to women, and patterns and associations are not necessarily applicable to men. In addition, data concerning sleep were based on the women’s own perceptions stated in questionnaires and doctor’s interview. Types of sleep medication were not fully documented directly in connection with the sleep interview. Finally, as mentioned earlier, participation rates differed over time in the different cohorts studied. However, decreasing participation in later examinations would probably tend to result in underestimated secular increases in sleep problems, rather than the reverse.
Despite these limitations, several conclusions may be drawn about trends over time, based on this cohort comparison. We could reliably conclude that middle-aged women well before menopause have shorter average sleeping time and perceive more sleeping problems than in earlier generations. In our study, the average sleep duration in 38-year-old women declined by about 15 min during the last 36 years. During the same period, the proportion of women complaining of sleeping problems almost doubled, but the use of sleeping medications remained unchanged since 1968. Middle-aged women of today generally seem to perceive more sleeping problems than earlier generations, which could for instance be explained by increased participation in working life and at the same time still taking major responsibilities for family and household work. In the Population Study of Women, working outside the home in these age groups increased from 55% in 1968 to 90% in 2004 (Björkelund et al., 2008).
The association between perceived sleeping problems and reported poor perceived economic, social and family situations, as well as with medical retirement across all examinations and both age groups, with increasing share of sleeping problems with perceived poorer situation is a confirmation of findings from several other population studies and should be an important issue in the context of improvements of women’s health. Short sleep duration and perceived sleep problems are both symptoms and causal factors of ill health. Changes in societal and work-related matters that improve women’s socioeconomic and family situations could be expected to be very health promotive for middle-aged women. As there was no apparent association between alcohol consumption and sleeping problems or regular leisure time physical activity, improvements on society level rather than on the individual level could be expected to be more efficient in improving women’s sleep.