To the best of our knowledge, this study is the first to investigate the association of the number of breaks taken during SB, measured objectively by a device, and serum lipid profiles in a healthy middle-aged female population. Previous studies have focused on PA and SB in child( 26,27), youth (28) or adult populations with certain physiological states or illnesses (29–31) or adults with different types of professions.(32, 33)
The quartile that had highest number of breaks per day had 0.11 mmol/l higher concentration of HDL and 0.10 mmol/l lower concentration of triglycerides compared to the quartile with lowest number of breaks in the adjusted model. Thus, participants in the quartile with the most breaks during SB had healthier lipid profiles than the quartile with the fewest breaks. This result might suggest better cardiovascular health in the future for the individuals with more breaks during SB. Therefore, it is hypothesized that in addition to the known positive effect of physical activity, our novel finding of the high amount of breaks during SB will have an impact on an individual’s CVD risk.
The mean amount of SB was higher in middle-aged women (60% of waking hours) than in the youth (53% of waking hours). However, these middle-aged women had more MVPA (8.9%) than the youth (5.3%).(28) The association of the amount of MVPA and the concentration of HDL-c was similar in our middle-aged women as was shown in pregnant women.(29)
The present study population represents the Finnish middle-aged female population well since the relevant baseline characteristics (BMI, age, TC, use of medications) are very similar to the Health 2011 study’s female population, which includes thousands of Finnish women.(8, 34) Thus, our results can be applied to the general population. Intervention studies on lifestyle changes in women invited to breast cancer screenings are ongoing, but they lack objectively measured PA data.(35) In addition, interventional studies on breast cancer patients showing a better quality of life among patients with the most physical activity have been published.(36)
Participants in the present study took an average of 7483 steps per day. This result is in line with those reported in other accelerometer studies.(8) It seems that important cardiometabolic improvements emerge when people take > 7500 daily steps, and it is suggested that one should aim for at least 7500 daily steps and 150 minutes of MVPA per week.(37) In this study the quartile with the most steps had a significantly higher concentration of HDL-c than the quartile with the fewest daily steps.
In Finland, all women aged 50–69 years are invited by personal letters to participate in breast cancer screenings with mammography tests biennially, free of charge. Participation is voluntary. However, the participation rate has been high since the implementation of nationwide screening in 1987. In 2017, the nationwide participation rate for the breast cancer screening programme was 82%. In addition, 3% of participants were invited for further testing, i.e., ultrasound examinations and biopsies, and 0.6% were diagnosed with breast cancer.(38) This type of screening would offer a unique platform for lifestyle counselling for middle-aged women.
CVDs are very common in Finland. They account for 34% of deaths annually in Finland. In 2012 nearly 22 000 cases of myocardial infarction and coronary artery disease episodes were reported. Almost half of them in females.(39) It is therefore important to investigate ways to influence cardiovascular health in our population.
The limitation of this type of study is that the participants are likely to comprise healthy volunteers who are already interested in their health. The volunteers are also likely to be more physically active. Altogether, 4161 women were invited for screenings with mammograms during the weeks we recruited study participants. Of these women, 3366 (81%) attended a screening, and 880 (26%) were willing to participate in this study. The mean BMI of the study population was slightly lower (26 kg/m2 (SD 4.6)) than in the FinHealth2017 Survey population study with the mean BMI of 28 kg/m2 among Finnish women in 2017.(40)
The recruitment method for the study was not very intensive. There were posters and flyers about the study in the screening mammography waiting room. Nurses at the screening facility mentioned about the recruiting process if they had the time to do so. This explains the loss of many participants and why the ones who wanted to participate are already quite physically active. However, there were 880 participants in this study, which is a reasonable amount.
The accelerometers were instructed to be used during waking hours and not during water-based activities. Therefore, some of the PA data were lost from the measurement period. However, the data are more objective and reliable than data in previous studies because these data are based on objective measurements and not on questionnaires only.(41)
We lost a few participants and their data because a mail workers’ strike occurred during our study period. Because of the postal delay in the delivery, the battery for the accelerometers did not last for the whole measurement period.
The study data from the questionnaires are not objective. It might be tempting for the participants to embellish their responses, e.g., their weight, height or smoking status. Menopausal status was not addressed in our questionnaire, but due to the study’s target age group (50–60 years), it is likely that most of the participants were postmenopausal.