Secular trends in sedentary behaviors and associations with weight indicators among Chinese reproductive-age women from 2004 to 2015: findings from the China Health and Nutrition Survey.

BACKGROUND: Overweight and obesity are rising among Chinese reproductive-age women, while some studies have focused on the relationship between sedentary behavior and obesity in certain populations, none has focused on Chinese reproductive-age women specifically. This study examined secular trends in leisure time sedentary behaviors (watching television time, computer time and reading time, and the total sedentary time) among Chinese reproductive-age women and the association of those behaviors with five weight indicators-body mass index (BMI), waist circumference (WC) and overweight, obesity, and abdominal obesity status.
METHODS: A prospective cohort study was conducted with Chinese reproductive-age women aged 15-49 who had participated in two or more rounds of the China Health and Nutrition Survey (CHNS), and completed the questionnaire and anthropometric measurements. The exposure variables were the average weekly time spent on three leisure time sedentary behaviors (watching television, using computer, and reading) and the total sedentary time (the sum of the above three sedentary time and video game time). Mixed-effect linear models were produced to explore the secular trends of the mean hours of these sedentary behaviors and the total sedentary time after adjusting covariates. Models were also produced to study the effects of these types of sedentary behavior levels on BMI and WC. Mixed-effect logistic regression models were produced to study the effects of the sedentary behavior levels on overweight, obesity, and abdominal obesity status.
RESULTS: The total sedentary time among the reproductive-age women increased over time across most of age, region, educational levels, and income groups from 2004 to 2015. Television hours fluctuated, it increased and then declined over time across most of age, region, and income groups. Computer hours continually increased over time across all age, region, educational level, and income groups. Reading hours gradually decreased over time across most of age, region, educational level, and income groups. Those with a moderate level of television time (14 to <35 h/week) had 1.08 cm larger WCs and were 1.31 times more likely to have abdominal obesity than those with a low level of television time (<14 h/week). Those with a high level of television time (≥35 h/week) had 1.74 cm larger WCs, 0.66 kg/m2 larger BMIs, were 1.50 times more likely to be overweight and were 1.47 times more likely to have abdominal obesity than those with a low level of television time (<14 h/week). Greater computer, reading time, and total sedentary time were not associated with WC, BMI, overweight, obesity, or abdominal obesity.
CONCLUSIONS: These findings showed that among Chinese reproductive-age women ages 15-49, secular trends of computer time increased rapidly, reading time decreased gradually and television time fluctuated but showed not much difference from 2004 to 2015. The sharp increase in computer time far outweighed the decline in reading time. As a result, the overall sedentary behavior time of Chinese reproductive-age women gradually increased. These findings provided strong evidence that greater television time was significantly associated with higher BMI, WC, and higher risks of overweight, abdominal obesity among Chinese reproductive-age women. Computer, reading, and the total sedentary time were not associated with those weight indicators.