Associations of Outdoor Activity, Screen Time with Body Weight: A Cross-Sectional Study of Chinese Preschool Children ^†

Abstract

This study was conducted to explore the relationship between outdoor activity time, screen time and body weight of children. All the participants, 3–6 years of age (n = 1422), from four kindergartens in Hangzhou City, Zhejiang Province, were selected as the subjects by random cluster sampling. Weight and height were measured. Total screen time, time of outdoor play were self-reported by parents in a questionnaire. We used the X² test, t-test and logistic regression analysis to analyze the data. After adjusting the influencing factors such as children’s age, father’s education level and screen time, the risk of overweight and obesity was 1.734 times (95% CI: 1.178–2.552) higher for the children with outdoor activity time ≤ 2 h/d: 2.050 (95% CI: 1.252–3.357) for boys, 1.472 (95% CI: 0.785–2.761)—for girls. After adjusting the influencing factors such as children’s age, father’s education level and outdoor activity time, the risk of overweight and obesity in the children with screen time ≥ 1 h/d was 1.639 times (95% CI: 1.272–2.113) that in the children whose screen time was less than 1 h/d, including 1.474 times (95% CI: 1.057–2.057) higher for boys and 1.676 times (95% CI: 1.119–2.511) higher for girls. Thus, both long screen time and outdoor activity time were associated with the increase in the risk of overweight and obesity.

1. Introduction

Child obesity has become one of the most challenging public health problems, and this issue is no longer a patent of developed countries. Many developing countries are also at risk of the increasing prevalence of childhood obesity.

With the popularization of electronic media products such as television, computers, and mobile phones, the opportunities for children to access electronic products continue to increase. Watching TV, playing with computers, and using mobile phones have become an indispensable part of children’s lives. However, watching TV, using computers, mobile phones and other screen devices for a long time has a great impact on childhood obesity [1]. However, the superimposed effects of screen time and outdoor activities on childhood overweight and obesity still lack the corresponding research [2].

2. Materials and Methods

This study adopted a random cluster sampling method and selected all 3–6-year-old children from four kindergartens in Hangzhou, a city in eastern China, as the research subjects. A total of 1422 children were tested, including 716 boys and 706 girls. The average age was 4.48 ± 0.91 years. The research subjects were divided into seven age-based groups with the step of half a year: 3 years old means 3–3.4 years old; 3.5 years old means 3.5–3.9 years old; 4 years old means 4–4.4 years old; 4.5 years old means 4.5–4.9 years old; 5 years old means 5–5.4 years old; 5.5 years old means 5.5–5.9 years old; 6 years old means 6–6.5 years old.

We adopted the questionnaire survey method. From April to June 2019, after the children’s afternoon school was over, the team members who received uniform training gathered the caregivers of the children surveyed in the classroom, and explained the survey purpose and requirement to the caregivers. And all the caregivers finisher the questionnaire on a voluntary basis after being informed. In this process, the relevant research personnel would remain ready to address the doubts of the parents in the process of filling in the questionnaire on time. After the questionnaires would be filled, the relevant survey personnel would collect them on the spot to ensure that there were no missing items.

The questionnaire for this research adopted the content of “The Fifth National Fitness Monitoring Work Plan (Kindergarten Part)”. The investigated family factors related to children’s overweight and obesity included whether the child participated in special sports training courses, the reproductive age of the parents, the education level of the parents, the parents’ occupations, whether the parents regularly exercised and the child caregivers. The education level was divided into three levels: junior high school and below, high school (including technical secondary school), university (including junior college and above); child caregivers were divided into parents, the elderly at home, and others (relatives, nanny, etc.)

The outdoor activity time aspect of this study required the parents to carefully recall the average daily outdoor activity time in the past week when their children were at home. According to the children’s physical activity guide, the average daily outdoor activity time was divided into “>2 h” and “≤2 h” [3].

The screen time aspect of this study required the parents to recall the average daily time their children spent watching TV, using mobile phones, tablets, computers, video games, etc. in the past week. According to the World Health Organization and China’s recommendations, children’s daily screen time should not exceed 1 h. The standard divides the average daily screen time into “<1 h” and “≥1 h” [2].

3. Results

3.1. Physical Characteristics of the Children

Table 1. Subjects’ height and body weight and gender differences (M ± SD).

Age	Height				Body Weight
	Boys	Girls	p		Boys	Girls	p
3	98.78 ± 4.13	97.73 ± 3.57	0.09		15.66 ± 1.85	15.15 ± 1.91	0.092
3.5	102.59 ± 4.69	100.24 ± 4.36	0.00		16.46 ± 2.19	15.50 ± 2.22	0.002
4	106.01 ± 4.60	104.49 ± 4.19	0.01		18.05 ± 3.45	16.70 ± 2.07	0.001
4.5	108.95 ± 4.08	107.99 ± 4.18	0.06		19.40 ± 2.94	18.20 ± 2.61	0.001
5	112.69 ± 4.51	111.16 ± 4.17	0.01		20.25 ± 3.12	19.03 ± 2.56	0.002
5.5	116.47 ± 4.25	115.20 ± 4.54	0.03		22.02 ± 3.71	20.61 ± 2.69	0.002
6	116.77 ± 4.38	115.34 ± 4.43	0.00		22.18 ± 3.35	20.62 ± 3.15	0.000
Total	109.04 ± 7.33	107.94 ± 7.32	0.00		19.18 ± 3.74	17.86 ± 3.11	0.000

shows that with the increase of age, the height and weight of children show a continuous increasing trend, and there are gender differences in height and weight of children 3.5 years old and later (p < 0.05).

There is no gender difference in the BMI of children before the age of 4, but from the age of 4, the BMI of children begins to have gender differences, and the BMI of boys is higher than that of girls (

Table 2. Subjects’ BMI and gender differences (M ± SD).

Age	Boys	Girls	p
3	16.03 ± 1.43	15.83 ± 1.38	0.359
3.5	15.59 ± 1.37	15.38 ± 1.68	0.308
4	15.96 ± 2.05	15.27 ± 1.43	0.005
4.5	16.29 ± 1.88	15.57 ± 1.68	0.001
5	15.89 ± 1.76	15.38 ± 1.48	0.022
5.5	16.15 ± 1.85	15.52 ± 1.74	0.011
6	16.23 ± 1.98	15.26 ± 1.77	0.003
Total	16.02 ± 1.79	15.46 ± 1.59	0.000

). Overall, the proportion of boys who are overweight and obese is higher than that of girls (

Table 3. Report rates of overweight and obesity in the children of different gender groups (n, %).

Gender	Normal Weight	Overweight and Obesity	X2	p
Boys	498 (69.6)	218 (30.4)	35.490	0.000
Girls	586 (83.0)	120 (17.0)

).

3.2. Outdoor Activity Time and the Children’s Overweight and Obesity

Table 4. Comparison of weight between the different outdoor activity time groups (n, %).

Group	Normal Weight	Overweight and Obesity	X2	p
Boys
Outdoor activity time < 2 h/d	402 (67.7)	187 (32.3)	5.795	0.016
Outdoor activity time ≥ 2 h/d	96 (78.7)	26 (21.3)
Girls
Outdoor activity time < 2 h/d	504 (82.5)	107 (17.5)	0.854	0.335
Outdoor activity time ≥ 2 h/d	82 (86.3)	13 (13.7)
Total
Outdoor activity time < 2 h/d	906 (75.2)	299 (24.8)	4.749	0.029
Outdoor activity time ≥ 2 h/d	178 (82.0)	39 (18.0)

shows that outdoor activity time has an impact on the overweight and obesity rate of boys (X² = 5.795, p = 0.016). But it has no effect on girls.

After adjusting for children’s age, parent’s education level, screen time and other factors, the risk of overweight and obesity for children with outdoor activities ≤ 2 h/d is 1.734 times that of children with outdoor activity> 2 h/d (95%CI: 1.178–2.552), of which boys are 2.050 times (95%CI: 1.252–3.357), and girls are 1.472 times (95%CI: 0.785–2.761); outdoor activity time ≤ 2 h/d is a risk factor for overweight and obesity in boys (p < 0.05,

Table 5. Logistic regression of the relationship between outdoor activity time and overweight and obesity.

Independent Variable	Unadjusted OR (95% CI)	Adjusted OR (95% CI)
Boys
Outdoor activity time ≥ 2 h/d	1	1
Outdoor activity time < 2 h/d	1.763 (1.106–2.811) *	2.050 (1.252–3.357) *
Girls
Outdoor activity time ≥ 2 h/d	1	1
Outdoor activity time < 2 h/d	1.339 (0.720–2.492)	1.472 (0.785–2.761)
Total
Outdoor activity time ≥ 2 h/d	1	1
Outdoor activity time < 2 h/d	1.506 (1.040–2.181) *	1.734 (1.178–2.552) *

Note: * p < 0.05; the adjusted factors include children’s age, father’s education level, screen time.

).

3.3. Screen Time and the Children’s Overweight and Obesity

As shown in

Table 6. Comparison of weight between the different screen time groups (n, %).

Group	Normal Weight	Overweight and Obesity	X2	p
Boys
Screen time < 1 h/d	278 (73.9)	98 (26.1)	7.183	0.007
Screen time ≥ 1 h/d	220 (64.7)	120 (35.3)
Girls
Screen time < 1 h/d	368 (85.6)	62 (14.4)	5.184	0.023
Screen time ≥ 1 h/d	218 (79.0)	58 (21.0)
Total
Screen time < 1 h/d	646 (80.1)	160 (19.1)	15.765	0.000
Screen time ≥ 1 h/d	438 (71.1)	178 (28.9)

and

Table 7. Logistic regression of the relationship between screen time and overweight and obesity.

Independent Variable	Unadjusted OR (95% CI)	Adjusted OR (95% CI)
Boys
Screen time < 1 h/d	1	1
Screen time ≥ 1 h/d	1.547 (1.123–2.131) *	1.474 (1.057–2.057) *
Girls
Screen time < 1 h/d	1	1
Screen time ≥ 1 h/d	1.579 (1.064–2.345) *	1.676 (1.119–2.511) *
Total
Screen time < 1 h/d	1	1
Screen time ≥ 1 h/d	1.641 (1.284–2.098) *	1.639 (1.272–2.113) *

Note: * p < 0.05; the adjusted factors include children’s age, father’s education level, outdoor activity time.

, taking screen time <1 h/d as the dividing standard, after adjusting for children’s age, parent’s education level, outdoor activity time and other factors, screen time ≥ 1 h/d children with overweight and obesity risk screen time <1 h/d children’s 1.639 times (95%CI: 1.272–2.113), among which boys are 1.474 times (95%CI: 1.057–2.057), girls are 1.676 times (95%CI: 1.119–2.511); screen time ≥1 h/d is for boys Risk factors for overweight and obesity in girls (p < 0.05).

4. Discussion

Studies have shown that the occurrence of myopia is related to the decrease in outdoor activities and the increase in TV, computer and mobile phone time [4]. This study shows that outdoor activity time and screen time increase the risk of overweight and obesity in 3–6-year-old children. Relevant studies have found that parental education has a certain influence on childhood obesity. It is believed that the incidence of obesity in children with mothers with low education is more common than that with mothers with high education [5]. This study found that mother’s education level has no effect on childhood obesity, but father’s education level has a significant impact on childhood obesity. The related mechanisms need to be investigated further. Therefore, when we studied the OR value of screen time and outdoor activity time with regard to the incidence of overweight and obesity in children, we adjusted the impact of parent’s education and age (Table 5 and Table 7).

We must consider the impact of lockdown measures instituted during the COVID-19 pandemic on childhood obesity and myopia.