Sedentary Behavior and Obesity in Youth According to Meeting Physical Activity Guidelines: National Health and Nutrition Examination Survey 2003

Abstract

Background:

The purpose of this study was to examine the association between sedentary time and obesity in youth according to meeting physical activity guidelines.

Methods:

A total of 1991 youth (10–17 years) from the 2003 to 2006 National Health and Nutrition Examination Survey were included in the analysis. Physical activity was categorized into two levels: (1) daily engagement in ≥60 minutes of moderate and vigorous physical activity (MVPA) and (2) <60 minutes per day of MVPA. Sedentary time was categorized into four levels using quartiles. BMI was categorized into two levels using sex-specific BMI for age percentiles from the CDC: (1) obese group: BMI ≥90 percentile and (2) nonobese group: BMI <90 percentile.

Results:

After adjusting for covariates, among those meeting physical activity guidelines, there was a statistically significant relationship between sedentary time and obesity for Q1 (sedentary time <383.5 min/day) vs. Q4 (sedentary time >523.5 min/day) [odds ratio (OR) = 0.14, 95% confidence interval (CI): 0.02–0.87] and Q2 (sedentary time = 383.5–451.83 min/day) vs. Q4 (sedentary time >523.5 min/day) (OR = 0.16, 95% CI: 0.03–0.99). Among youth not meeting physical activity guidelines, however, sedentary time was not associated with obesity [OR = 0.72 (Q1 vs. Q4), OR = 0.88 (Q2 vs. Q4), OR = 1.08 (Q3 vs. Q4)].

Conclusions:

These results indicate that sedentary time is associated with obesity among those meeting physical activity guidelines. However, the relationship between sedentary time and obesity in a low physical activity group is not obvious. Therefore, to confirm the role of low-level physical activity on the relationship between sedentary time and health outcomes, further investigation is required.

Introduction

Factors affecting health in modern society include physical activity^1–3—and sedentary behavior (SB).⁴ Physical activity has been defined as “any bodily movement produced by skeletal muscles that result in caloric expenditure.”⁵ Physical activity is inversely associated with various health outcomes such as obesity,^6,7 metabolic syndrome,^8,9 and cardiovascular disease.¹⁰ The recent 2018 Physical Activity Guidelines for Americans¹¹ recommends that youth engage in at least 60 minutes per day moderate and vigorous physical activity (MVPA), including short episodes of activities (i.e., bouts <10 minutes) that contribute to health outcomes.

SB has been defined as “any waking behavior characterized by energy expenditure of 1.5 metabolic equivalents (METs), while in a sitting or reclining posture.”¹² According to recent studies, the detrimental associations of SB with obesity have been indicated independent of MVPA.^13,14 Obesity in childhood is known to track into adolescence¹⁵ and adulthood,¹⁶ and is associated with several health problems such as cardiovascular disease,¹⁷ hypertension,¹⁸ and metabolic syndrome.⁸ Therefore, in addition to promoting MVPA, efforts should be made to reduce SB.¹⁹

Although previous work has statistically controlled for physical activity when evaluating the association between sedentary time and obesity,²⁰ this analytical approach does not determine whether there is an interaction effect of physical activity and sedentary time on obesity. That is, whether sedentary time is associated with obesity among those who meet and do not meet physical activity guidelines. This was of central interest to this study. In addition, the majority of work on this topic has employed self-report measures of physical activity and sedentary time, which are prone to considerable measurement error, including social desirability and recall bias.²¹ Furthermore, when obesity in youth seems to be tracked over time, the rise in youth obesity rates is expected to exacerbate adult obesity rates in the future.²² Therefore, attention should be paid to obesity in youth. Therefore, the purpose of this study was to address these gaps in the literature by specifically evaluating whether device-assessed sedentary time is associated with obesity among those meeting and not meeting physical activity guidelines in youth.

Methods

Design and Participants

Data extracted from two cycles of the 2003 to 2006 National Health and Nutrition Examination Survey (NHANES). These cycles were employed as, at the time of this writing, these are the only available cycles with accelerometry data. The NHANES is an ongoing survey conducted by the CDC that uses a representative sample of noninstitutionalized United States civilians selected by a complex, multistage, stratified, clustered probability design. The NHANES procedures were approved by the ethics review board of the National Center for Health Statistics. More information on the NHANES methodology data collection can be found on the NHANES website (www.cdc.gov/nchs/nhanes.htm). Among the 2003–2006 NHANES cycles, we delimited the analyses to youth between 10 and 17 years, which included 1991 youth.

Physical Activity and Sedentary Time Measures

The Actigraph (model 7164; Actigraph, LLC, Fort Walton Beach, FL) accelerometer was used to measure physical activity and sedentary time of all ambulatory participants. The participants were instructed to wear the accelerometer on their right hip for 7 consecutive days, with the exclusion of water-related activities or sleeping. A detailed description of the accelerometer protocol for the 2003–2004 NHANES is available at www.cdc.gov/nchs/data/nhanes/nhanes_03_04/lab.pdf.

The SB metric that we used was time spent in SB. The time spent on MVPA and SB during wear time was defined as ≥2020 and <100 counts per minute (cpm), respectively.^23,24 For each valid day, the cumulative total MVPA and sedentary time were estimated to indicate the average time spent in a day in MVPA and SB. Valid days were defined as the device being worn over 10 or more hours.

Nonwear time was defined as a period with ≥60 consecutive minutes of 0 cpm with allowance for 1 or 2 minutes with <100 cpm. Participants were included in the analysis if they had at least 4 valid days, including at least one weekend day. The procedures used to analyze accelerometer data were based on the protocols used in similar studies.^24,25 For analytical purposes, physical activity was categorized into two levels: (1) ≥60 minutes per day of moderate and vigorous physical activity (MVPA) and (2) <60 minutes per day MVPA. Sedentary time was categorized into quartiles.

Obesity Measures

Obesity was assessed from BMI (kg/m²). Weight (kg) and height (m) were measured in accordance with standard procedures. BMI was categorized into two levels using sex-specific BMI for age percentiles from the CDC: (1) obese group: BMI ≥90 percentile by age and sex and (2) nonobese group: BMI <90 percentile by age and sex.

Data Analysis

All statistical analyses were performed using SURVEY procedures in SAS version 9.4 (SAS Institute, Inc., Cary, NC) to account for the complex nature of the NHANES sampling scheme. SAS SURVERYLOGISTIC procedure was performed to evaluate the association between sedentary time and obesity by physical activity level, while controlling for age, sex, race, income, and a total number of wear minutes in a day. Statistical significance was set a priori at an α level of 0.05.

Results

Across the 2003–2006 NHANES cycles, youth 10–17 years of age were included in the analyses. Among those with complete data on the study variables (age, sex, race, income, BMI, sedentary time, and physical activity), the total sample size was 1991 (1017 boys). Table 1 presents the study variable characteristics across physical activity level. The average BMI among those meeting physical activity and not meeting physical activity guidelines was 19.93 ± 4.07 and 22.30 ± 5.20 kg/m² (p < 0.001), respectively. The average sedentary time among those meeting physical activity and not meeting physical activity guidelines was 385.95 ± 92.08 and 475.25 ± 112.30 minutes (p < 0.001), respectively.

Table 1.

Descriptive Characteristics of the Sample across the Two National Health and Nutrition Examination Survey Cycles

Variable	Meeting PA guideline	Not meeting PA guideline	p
Age (years)	11.58 ± 1.70	13.73 ± 2.23	<0.001^*
Sex, n (%)			<0.001^*
Boys	294 (73.1)	723 (45.5)
Girls	108 (26.9)	866 (54.5)
Race/ethnicity, n (%)			0.55
Non-Hispanic white	93 (23.1)	392 (36.1)
Non-Hispanic black	157 (39.1)	520 (32.7)
Mexican American	125 (31.1)	573 (36.1)
Other race	14 (3.5)	63 (4.0)
Other Hispanic	13 (3.2)	41 (2.6)
Household income, n (%)			0.78
<$25,000	117 (29.1)	397 (30.21)
$25,000 to <$45,000	92 (22.9)	351 (26.71)
$45,000 to <$75,000	76 (18.9)	273 (20.78)
$75,000 to over	95 (23.6)	293 (22.30)
BMI (kg/m²)	19.93 ± 4.07	22.30 ± 5.20	<0.001^*
Nonobese, n (%)	303 (76.15)	1073 (70.21)
Obese, n (%)	99 (23.85)	516 (29.79)
SB time (minutes)	385.95 ± 92.08	475.25 ± 112.30	<0.001^*
Min	189.50	209.40
Max	826.71	1245.17
MVPA (minutes)	89.13 ± 28.84	25.71 ± 16.74	<0.001^*

SB time reported median and interquartile range.

p-Value <0.05 indicates difference between meeting PA guideline group and not meeting PA guideline group.

Max, maximum; Min, minimum; MVPA, moderate and vigorous physical activity; PA, physical activity; SB, sedentary behavior.

Table 2 displays the adjusted odds ratio (OR) between sedentary time and obesity by physical activity level. After adjustments, the OR was statistically significant between sedentary time and obesity in those meeting physical activity guidelines. In those meeting physical activity guidelines, youth in the 1st (<383.5 min/day) and 2nd (383.5–451.83 min/day) sedentary time quartiles were less likely to be obese compared to youth in the upper sedentary time quartile (>523.5 min/day), OR = 0.14, 95% confidence interval (CI): 0.02–0.87 and OR = 0.16, 95% CI: 0.03–0.99, respectively. However, youth in the 3rd (451.83–523.5 min/day) sedentary time quartile did not have a significant association between sedentary time and obesity when compared to those in the upper sedentary time quartile. Among those not meeting physical activity guidelines, there was no statistical association between sedentary time and obesity [OR = 0.72 (Q1 vs. Q4), OR = 0.88 (Q2 vs. Q4), OR = 1.08 (Q3 vs. Q4)].

Table 2.

Adjusted Odds of Obesity across Quartile of Accelerometer-Derived Sedentary Behavior Time

PA guideline	Health outcomes	SB	OR	95% CI
Meeting PAG	Obesity	1st Quartile (≤383.5 min/day)	0.14^*	0.02–0.87
		2nd Quartile (383.6–451.83 min/day)	0.16^*	0.03–0.99
		3rd Quartile (451.84–523.5 min/day)	0.49	0.11–2.15
		4th Quartile (≥523.6 min/day)	Ref.
Not meeting PAG	Obesity	1st Quartile (<383.5 min/day)	0.72	0.41–1.27
		2nd Quartile (383.5–451.83 min/day)	0.88	0.47–1.65
		3rd Quartile (451.83–523.5min/day)	1.08	0.66–1.78
		4th Quartile (>523.5 min/day)	Ref.

Indicates that OR is significant at 0.05 controlling for gender, age, race, income, and total number of wear minutes in a day.

CI, confidence interval; OR, odds ratio; PAG, physical activity group; Ref., reference.

Discussion

The purpose of this study was to evaluate the relationship between objectively measured sedentary time and obesity among youth who meet and do not meet physical activity guidelines. Our findings demonstrated that higher sedentary time was associated with increased odds of obesity among those who meet physical activity guidelines.

Our descriptive demographics indicate that those who do not meet physical activity guidelines were older than those meeting physical activity guidelines, and boys were more active than the girls. These results support previous studies that indicate physical activity decreases as an individual gets older.^26,27 Also, other research demonstrates that boys are more active than girls.^26,28,29 Among those meeting physical activity guidelines, nearly one-third of youth were obese. Future research is needed to investigate the activities of overweight/obese youth and the factors that may affect them.

According to previous studies, regardless of physical activity, the shorter the sedentary time such as screen time in adolescent, the lower the probability of obesity.³⁰ Our results indicate that physical activity may not attenuate the detrimental effects of sedentary time on obesity. That is, sedentary time was only associated with obesity among those who meet physical activity guidelines. Also, previous studies support our results in that sedentary time and MVPA were independently associated with all-cause mortality³¹ and a positive relationship between sedentary time and metabolic risk in physically active people.³²

Also, when physical activity was “statistically controlled” in the analyses, this does not mean that sedentary time influences obesity “regardless” of physical activity. The only way to look at this “regardless” effect is through the moderation approach we employed or to evaluate an interaction. Therefore, when we use one of the methods to identify the “regardless” effect, we demonstrate that sedentary time is only associated with obesity among youth meeting physical activity guidelines.

In our study, however, the relationship between sedentary time and obesity among those not meeting physical activity guidelines is unclear. It is possible that the effect of low physical activity on obesity is greater than the effect of SB, thus washing out the association between SB and obesity. Perhaps, the association between SB and obesity is not independent of physical activity in this group. Therefore, this will require additional investigation and future research should consider these possibilities within our evaluated topic.

There are several limitations of our study. Due to cross-sectional nature of the NHANES data, we could not determine the cause and effect relationship between sedentary time and obesity. Also, the accuracy and relevance of this data may be questionable because the data reported in this study were collected between 2003 and 2006. In terms of strengths, sedentary time and physical activity were objectively measured by accelerometry and provide objective evidence of the relationship between sedentary time and obesity. Also, we employed a nationally representative sample of youth.

Conclusions

In summary, sedentary time was positively associated with obesity among youth who were meeting physical activity guidelines. For a group of the low level of physical activity, however, the relationship between sedentary time and obesity is not evident. Therefore, further investigation is required to confirm the role of low-level physical activity on the relationship between sedentary time and health outcomes.

Footnotes

Funding Information

This research received no external funding.

Author Disclosure Statement

No competing financial interests exist.

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Sedentary Behavior and Obesity in Youth According to Meeting Physical Activity Guidelines: National Health and Nutrition Examination Survey 2003–2006

Abstract

Background:

Methods:

Results:

Conclusions:

Introduction

Methods

Design and Participants

Physical Activity and Sedentary Time Measures

Obesity Measures

Data Analysis

Results

Discussion

Conclusions

Footnotes

Funding Information

Author Disclosure Statement

References