This study examined the prospective association of leisure time spent on various sedentary activities with cardiometabolic risk factors in adults. Our findings demonstrate that there are almost no prospective associations between overall sedentary time or sedentary time in different domains (i.e. TV viewing, computer use, reading and other sedentary behaviours) with individual or clustered cardiometabolic risk factors.
Our finding that higher levels of overall sedentary time were negatively associated with HDL-C over a two-year period was weak as the regression coefficient for this association was small. This is only partly in line with previous studies examining objectively measured sedentary time and cardiometabolic risk among individuals at increased risk for T2DM. Henson et al.  found a significant association between objectively assessed sedentary time and HDL-C as well as 2 hr glucose, but they found no association with waist circumference, BMI, fasting glucose and HbA1c among middle aged and older adults at high risk of impaired glucose regulation. Ekelund et al.  found no associations between objectively assessed sedentary time and fasting plasma insulin among individuals with a parental history of T2DM.
Separate analyses for TV time revealed a statistically significant association with only one out of 13 cardiometabolic risk factors studied (i.e. HDL-C). The lack of consistent associations with cardiometabolic risk is in line with a previous study of our group , but in contrast to findings of others ,,. Pinto Pereira et al. demonstrated a significant association between TV time and increase in BMI  and six out of nine cardiometabolic risk factors in women and four out of nine in men . Heinonen et al.  found significant associations of TV time with waist circumference and BMI. Among adults at increased T2DM risk, Ekelund et al.  found significant associations of TV time with fasting insulin and insulin resistance (HOMA-IR) at baseline, but not follow-up.
We found no associations of computer time with any of the cardiometabolic risk factors. This finding is in line with Altenburg et al. , but in contrast to Heinonen et al. , who found significant associations with waist circumference and BMI in women but not men.
In line with Heinonen et al. , we found no significant association between reading time and indicators of overweight. To date, no studies have been published on the separate association of reading time with cardiometabolic risk factors, T2DM and CVD and risk scores. The limited time spent on reading in this population might be an explanation for the lack of an association.
Time spent on sedentary behaviours other than TV viewing, computer use and reading was not related to cardiometabolic risk factors. Unfortunately, except for the examples given (e.g. sitting while talking with friends, playing board games, sitting in the car), we have no specific information on the sedentary behaviours in this category. Therefore, sedentary time in this domain, as well as total sedentary time, might be underestimated. Future studies should further examine less frequently explored sedentary behaviours including passive transport, sitting during meals and relaxing, in order to obtain a complete overview of sedentary time. Additionally, sedentary behaviours using electronic devices such as phones and tablets should be further explored.
One important difference with the previous studies mentioned above is that we adjusted for total physical activity (i.e. light, moderate and vigorous) instead of moderate-to-vigorous physical activity only. This is important when examining the true association between sedentary time and cardiometabolic risk . Our finding that there is virtually no association between sedentary time and cardiometabolic risk is in line with Maher et al. , who demonstrated that potential (weak) associations disappear when analyses are adjusted for total physical activity. Another explanation for the lack of an association of self-reported sedentary time with cardiometabolic risk may be the limited variance in sedentary time over the 2-year follow-up period. Furthermore, similar to physical activity that is generally overestimated , sedentary time may be underestimated especially when assessed in one question. Adding up sedentary time in different domains, i.e. in separate questions, may result in a more accurate estimate of actual sedentary time, when covering all sedentary behaviours.
The prospective design with four measurements over 2 years is an important strength of the present study. The distinction between different domains of sedentary behaviour (i.e. TV viewing, computer use, reading and other sedentary behaviours) further strengthens our study. Although self-reported measures of sedentary behaviour are sensitive to recall bias, these measures are required to study the association of different types of sedentary behaviours and cardiometabolic risk factors. The AQuAA questionnaire correlated moderately on test-retest reliability assessment (ICC = 0.60, CI = [0.40; 0.74]) regarding time spent on sedentary behaviours . However, correlation between the AQuAA and Actigraph was low and non-significant (Spearman correlation coefficient = 0.15). Finally, the category of time spent in sedentary behaviours other than TV viewing, computer use and reading is vague and may not cover all other sedentary behaviours.
We conclude that sedentary time (overall and in different domains) was virtually not prospectively associated with cardiometabolic risk among adults at increased cardiometabolic risk. Future studies, using more accurate measures of different sedentary behaviours, should further examine the possible distinct association of different sedentary behaviours and cardiometabolic risk factors.