Cardiometabolic Risk Factors among Insufficiently Active African American Women with Obesity: Baseline Findings from Smart Walk

Abstract

Background:

Low moderate-to-vigorous physical activity (MVPA) levels and obesity are associated with increased cardiometabolic disease risk.

Objective:

To describe MVPA and cardiometabolic risk characteristics of insufficiently active African American women with obesity (N=60) enrolled in a culturally tailored MVPA intervention.

Methods:

We assessed accelerometer-measured and self-reported MVPA, blood pressure, serum lipid profiles, cardiorespiratory fitness (VO₂ peak), and aortic pulse wave velocity.

Results:

Participants (M age=38.4; M BMI = 40.6 kg/m²) averaged 15 min/day of accelerometer-measured MVPA and 30 min/week of self-reported MVPA. Systolic and diastolic blood pressure were elevated (135.4 and 84.0 mm/Hg, respectively). With the exception of LDL- (121.4 mg/dL) and HDL-cholesterol (47.6 mg/dL), lipid profiles were within normal ranges. Compared to normative reference values, average VO₂ peak was low (18.7 ml/kg/min), and pulse wave velocity was high (7.4 m/s).

Conclusions:

Our sample of insufficiently active African American women with obesity was at elevated risk for cardiometabolic disease.

Introduction

Cardiometabolic diseases are a major public health concern for African American (AA) women. National data show 55% are obese,¹ 59% have cardiovascular disease,² and 13% have diagnosed diabetes (with type 2 accounting for 90-95% of all cases).³ These conditions affect AA women at higher rates than non-Hispanic white women, Hispanic women, and the US population as a whole.^1–3 For example, 38% of non-Hispanic White women are obese, 42% have cardiovascular disease, and 7% have diabetes. Rates among Hispanic women are 51%, 43%, and 12%, respectively. The burden of these conditions among AA women contributes to their high cardiovascular mortality rate, which is at least twice that of non-Hispanic White and Hispanic women.⁴

Lifestyle behaviors, including moderate-vigorous physical activity (MVPA), play a critical role in preventing and managing cardiometabolic diseases. In fact, high levels of MVPA, independent of weight status, are associated with reduced risk of cardiovascular disease, type 2 diabetes, cardiovascular mortality, and all-cause mortality.⁵ Existing research examining associations between MVPA and cardiometabolic disease risk among AA women has relied predominately on self-reported MVPA and traditional measures of cardiometabolic disease risk (i.e., blood pressure, lipid profiles, and insulin levels).^6,7 Few studies examining cardiometabolic risk profiles among AA women have included objectively-measured MVPA and more novel and prognostic risk factors implicated in cardiometabolic diseases, including cardiovascular fitness and arterial stiffness. Cardiorespiratory fitness and arterial stiffness (measured by aortic pulse wave velocity) have stronger predictive value for cardiovascular events than traditional measures of cardiometabolic disease risk.^5,8 They provide a stable estimate of cardiometabolic disease risk that accounts for habitual MVPA and the presence of other cardiometabolic risk factors (i.e., age, high blood pressure, smoking). This report describes MVPA levels and measures of cardiometabolic disease risk among insufficiently active (i.e., ≤ 60 minutes/week of self-reported MVPA) AA women with obesity (BMI ≥ 30 kg^/m²) enrolled in a culturally tailored MVPA intervention for which MVPA was measured objectively and cardiometabolic disease risk assessment included traditional and novel measures.

Methods

Sample and Study Design Overview

Data presented are the baseline MVPA and cardiometabolic disease risk characteristics of insufficiently active AA women (N=60) with obesity enrolled in a randomized pilot trial of Smart Walk, an 8-month culturally tailored, Social Cognitive Theory-based smartphone-delivered MVPA intervention (clinicaltrials.gov identifier NCT02823379).⁹ The intervention focused exclusively on women who were both insufficiently active and with obesity because they are at high risk for development of cardiometabolic diseases based on their low MVPA levels and elevated weight status.⁵ Participants were recruited using community-based strategies, including email distribution lists, social media advertisements, fliers placed at community locations, and in-person recruitment at community events. Inclusion criteria were: a) self-identifying as an AA woman; b) aged 24 to 49 years; c) BMI ≥ 30 kg^/m²; d) engaging in ≤ 60 minutes/week of MVPA according to the 2-item Exercise Vital Sign questionnaire¹⁰; and e) English-speaking and -reading. Exclusion criteria included: a) concurrent participation in another PA, nutrition, or weight loss program; b) indication of a potential contraindication of exercise according to the 2015 Physical Activity Readiness Questionnaire (PAR-Q+),¹¹ unless a written permission from the potential participant’s primary care physician is provided; c) pregnant at time of screening or plans to become pregnant in the next 8 months; and d) plans to relocate out of the Phoenix metropolitan area in the next 12 months.

Women interested in study participation contacted the research team and completed a telephone eligibility screening interview. Eligible women then attended an in-person study orientation session that provided detailed information about the study. After the orientation session, women participating in the study provided written informed consent and were given an ActiGraph GT9X Link accelerometer with instructions for wear for the next 7 days. After wearing the accelerometer, participants returned the accelerometer at their baseline study visit and completed survey and physiological study assessments (described below). See Joseph et al.⁹ for a detailed description of the Smart Walk intervention study.

Measures

Sociodemographics

Sociodemographic characteristics were assessed using a self-report form developed for the study. Variables assessed included age, relationship status, education, and household income.

Physical Activity

Self-reported PA.

Self-reported PA was assessed using the 2-item Exercise Vital Sign questionnaire.¹⁰ The Exercise Vital Sign questionnaire asks participants to report the frequency (days per week) and duration (minutes per day) of MVPA performed (e.g., a brisk walk) during the past week. The questionnaire is scored by multiplying the days x minutes of MVPA performed to create an estimate of minutes per week of MVPA. This measure has been validated against population-based surveillance surveys¹⁰ and accelerometers for accurate assessment of PA.¹²

Accelerometer-measured MVPA.

Objectively measured MVPA was assessed using the ActiGraph GT9X Link activity monitor. The GT9X Link is a 3-axis accelerometer that objectively measures the rate of body movement. Participants were asked to wear the activity monitor on their non-dominant wrist 24 hours per day for 7 consecutive days. To be considered a valid assessment, participants were required to wear the accelerometer for at least 10 waking hours per day on at least 4 days during the 7-day wear period. Raw accelerometer data were collected at 30 Hz and downloaded to a computer equipped with ActiLife (Version 6) software. To verify wear time, raw accelerometer data were scaled to a 60-second epoch length using ActiLife software and screened using the validated Choi et al.¹³ algorithm. After wear time was validated, raw accelerometer files were processed and analyzed using the GGIR software package¹⁴ available in the R open-source computing software program.¹⁵ Algorithms by Hildebrand et al.¹⁶ were applied to classify minutes/day of MVPA performed in 1- and 10-minute bouts using a 5-second epoch and a gravity-based acceleration threshold of 100 mg or greater to classify MVPA. MVPA performed in 1-minute bouts was calculated by summing the total number of daily minutes participants met or exceeded the 100 mg threshold continuously over a 60-seconds. MVPA minutes accrued in 10-minute bouts were calculated as the number of minutes where 80% of movements over ≥ 10 consecutive minutes were equal to, or higher, than the 100 mg threshold.

Measures of Cardiometabolic Disease Risk

BMI.

Body weight was measured with a Tanita TBF-300A digital scale to the nearest 0.1 kg. Height was measured with Seca 213 portable stadiometer to the nearest 0.1 cm. Waist circumference was measured at the midpoint between rib and the top of iliac crest to the nearest 0.1 cm at the end of participants’ normal expiration. BMI was calculated as weight in kilograms divided by height in meters squared.

Serum and Plasma Markers of Cardiometabolic Disease Risk.

A certified phlebotomist collected blood draws after a 10-hour fast. Serum and plasma were separated by centrifugation and stored at −80C. Fasting plasma glucose was measured using a Cobas C-111 chemistry analyzer (Roche Diagnostics, Indianapolis, IN) and serum lipid panel measures (triglycerides, total cholesterol, HDL-C) were assessed using a Rx Daytona chemistry analyzer (Randox Laboratories, Kearneysville, WV). LDL was calculated using the Friedewald equation.

Classification of Metabolic Syndrome.

National Cholesterol Education Program Adult Treatment Panel III criteria¹⁷ were used to identify the presence of the metabolic syndrome. These criteria included the presence of three or more of the following risk factors: 1) increased waist circumference (i.e., >88 cm for women); 2) hypertension (≥130/≥85 mmHg); 3) elevated triglycerides (i.e., ≥150 mg/dl); 4) low HDL cholesterol (i.e., < 50 mg/dl in women); and 5) impaired fasting glucose (≥100 mg/dl).

Cardiorespiratory Fitness.

A modified Balke treadmill protocol was used to estimate peak oxygen uptake (VO₂peak). This validated¹⁸ protocol maintains a constant speed of 3.0 mph and starts at 2% grade. The workload is then increased by a 1% grade every minute until the termination of the test. Criteria for test termination followed ACSM guidelines.¹⁹ Metabolic responses to exercise were assessed using an Oxycon mobile device (CareFusion) and breath-by-breath indirect calorimetry. VO₂peak was estimated using the Foster equation.²⁰

Pulse Wave Velocity.

A certified sonographer measured aortic pulse wave velocity. To begin this test, a blood pressure cuff was placed around the participant’s thigh and the distance between the carotid and femoral arteries was measured to the nearest centimeter. Next, the participant rested in the supine position in a quiet room for 15 minutes. After this 15-minute rest period, the aortic pulse wave velocity test was conducted using the SphygmoCor XCEL system (AtCor Medical, Itasca, IL). Specifically, the blood pressure cuff on the participant’s thigh was inflated to sub-systolic pressure (<150 mmHg) to capture the femoral artery waveform and the technician placed an applanation tonometer over the carotid artery. The SphygmoCor XCEL system then assessed the transit time for the pulse to travel from the carotid artery to the femoral artery. The system automatically determined pulse wave velocity by dividing the distance between the carotid and femoral arteries by the pulse transit time. Three measurements were taken with the SphygmoCor device, with the 2 closest values being averaged to obtain pulse wave velocity.

Statistical Analysis

Descriptive statistics (i.e., means, standard deviations, frequencies, percentages) were used to summarize sociodemographic characteristics, physical activity levels, and measures of cardiometabolic disease risk. Exploratory analyses using Pearson correlations were conducted to examine associations among MVPA outcomes and measures of cardiometabolic disease risk. Data analyses were conducted using R version 4.0.2.

Results

Table 1 provides an overview of sociodemographic characteristics, physical activity levels, and cardiometabolic disease risk profiles of participants.

Table 1.

Sociodemographic characteristics, physical activity levels, and measures of cardiometabolic disease risk among study participants (N = 60, except where noted).

Sociodemographic characteristics	M (SD) or n (%)
Age (years)	38.4 (6.9)
Relationship status
Married	22 (36.7%)
Committed relationship	8 (13.3%)
Divorced or separated	10 (16.7%)
Never married	20 (33.3%)
Annual household income
< $25,000	9 (15.0%)
$25,000-$50,000	23 (38.3%)
$50,001-$75,000	22 (36.7%)
≥ $75,001	6 (10.0%)
Highest level of education completed
Some high school	1 (1.7%)
High school diploma/GED	7 (11.7%)
Some college or technical school	23 (38.3%)
Bachelor’s degree	12 (20.0%)
Postgraduate degree	16 (26.7%)
Physical activity	M (SD)
Self-reported MVPA a (min/week)	30.3 (40.3)
ActiGraph-measured MVPA (min/day)
Bouts of 1 minute or greater	15.0 (10.3)
Bouts of 10 minutes or greater	2.1 (5.2)
Measures of cardiometabolic disease risk	M (SD) or n (%)
BMI (kg/m2)	40.6 (7.0)
Waist circumference (cm)	114.7 (15.4)
Brachial Systolic BP (mmHg)	135.4 (15.1)
Brachial Diastolic BP (mmHg)	84.0 (11.3)
Blood pressure categoryb
Normal	8 (13.3%)
Elevated	7 (11.7%)
Stage 1 hypertension	28 (46.7%)
Stage 2 hypertension	17 (28.3%)
Fasting glucose (mg/dl), n = 58c	108.0 (43.4)
Total cholesterol (mg/dl), n = 58	186.7 (37.1)
HDL cholesterol (mg/dl), n = 58	47.6 (9.9)
LDL cholesterol (mg/dl), n = 58	121.4 (30.2)
Triglycerides (mg/dl) , n = 58	88.7 (44.4)
Metabolic syndrome present, n = 58	39 (67.2%)
Relative VO2 peak (ml/kg/min), n = 58 d	18.7 (3.21)
Pulse wave velocity (m/s), n = 57 e	7.4 (1.2)

^aMVPA = moderate-to-vigorous physical activity.

^bBlood pressure categories are based on American Heart Association guidelines.

^cSerum and lipid data were not available for 2 participants due to unsuccessful blood draws.

^dCardiorespiratory fitness was missing for 2 participants due to mask anxiety (n=1) and computer software malfunction (n=1)

^ePulse wave velocity data missing for 3 participants due to failed quality control checks.

Sociodemographic Characteristics

Participants, on average, were aged 38.4 (SD=6.9) years. Half of the sample was either married or in a committed relationship and forty-seven percent reported obtaining a bachelor’s degree or higher. Household income levels varied (see Table 1), with most participants (95%) reporting a household income of less than $75,000.

Physical Activity

Participants self-reported engaging in 30 (SD=40.3) minutes per week of MVPA. ActiGraph accelerometer-measured MVPA indicated that participants performed 15 (SD=10.3) min/day when considering PA performed in bouts of 1 min or greater and 2.1 (SD=5.2) min/day in bouts of 10 min or longer.

Measures of Cardiometabolic Disease Risk

Participants had a mean BMI of 40.6 kg/m² (SD=7.0) and a mean waist circumference of 114.7 cm (SD=15.4). Brachial measured blood pressure estimates were 135.4 mm/Hg (SD=15.1) for systolic pressure and 84.0 mmHg (SD=11.3) for diastolic pressure. Seventy-five percent of participants were classified as having stage 1 (46.7%) or stage 2 (28.3%) hypertension. Despite mean total cholesterol being in the desirable range (186.7 mg/dl; SD=37.1), average LDL cholesterol was high (121.4 mg/dl; SD=30.2) and average HDL cholesterol was slightly below the 50 mg/dl threshold for low HDL (M=47.6 mg/dl; SD=9.9). Based on ATP III criteria, 67.2% of participants were classified as having metabolic syndrome. Cardiorespiratory fitness (VO₂ peak) and aortic pulse wave velocity outcomes were 18.7 ml/kg/min and 7.4 m/s, respectively.

Associations among Physical Activity and Measures of Cardiometabolic Disease Risk

Correlations among MVPA outcomes and measures of cardiometabolic disease risk are presented in Supplemental Digital Content Tables 1–3. Moderate-to-strong associations between accelerometer-measured MVPA (accrued in 1- and 10-minute bouts) and BMI (Pearson rs = −.31 and −.32, respectively), waist circumference (rs = −.32 and −.37 respectively), and cardiorespiratory fitness (rs = .39 and .43, respectively). Higher accelerometer-measured MVPA was associated with lower BMI, smaller waist circumference, and higher cardiorespiratory fitness. After adjusting p-values for multiple testing, these associations were no longer statistically significant. With exception for some associations between self-reported PA and measures of cardiometabolic disease risk, most other correlations were weak (rs < .25) and not statistically significant prior to (or following) adjustment for multiple testing.

Discussion

This article reports baseline PA and cardiometabolic disease risk characteristics of insufficiently active AA women with obesity enrolled in a culturally tailored physical activity intervention designed to increase PA and reduce cardiometabolic disease risk. Results showed that participants engaged in 30 minutes/week of self-reported MVPA. This amount equates to less than 5 min/day of MVPA and is approximately 80% lower than national PA guidelines of 150 min/week. Accelerometer-measured PA estimates confirmed participants’ low PA levels. When considering activity performed in bouts of 1 min or longer, participants engaged in 15.0 min/day of MVPA (or approximately 105 min/week). However, when analyzing activity in bouts of 10 min or greater, which corresponds with the minimum bout criteria for PA assessed using our self-report measure (Exercise Vital Sign) and aligns with the bout duration traditionally considered necessary to accrue health benefits from PA (that is, until release of the 2018 PA guidelines for Americans²¹), participants engaged in a mean of 2.2 min/day of MVPA (approximately 15 min/week). The low level of daily MVPA performed in 10-minute bouts reflects the small proportion of participants who performed any MVPA in bouts of ≥ 10 min during the 7-day accelerometer wear period. For example, 40 (66.7%) of the participants had no days with a bout of MVPA ≥ 10 min, 12 participants (20.0%) had only one day with bouts ≥ 10 min MVPA, 4 (6.7%) had two days, 2 (3.3%) had three days, and 1 (1.7%) had four days. MVPA levels of study participants were similar to results of other studies examining MVPA among populations with elevated indices cardiometabolic disease risk (i.e., high blood pressure, elevated BMI),^22,23 as well as those with the diagnosed presence of cardiometabolic diseases²⁴; further underscoring the relationship between MVPA and cardiometabolic disease risk.

Blood pressure results showed that 87% (n=52) of our sample had sub-optimal blood pressure levels, with most classified as having either Stage 1 (47.6%) or Stage 2 (28.3%) hypertension. Despite participants having a mean total cholesterol level within a generally accepted normal range (i.e., M total cholesterol of our sample was 187 mm/dl), average LDL levels (M=121.4 mg/dl) were 21% higher than recommended level of 100 mg/dL and average HDL levels (M=47.6 mm/dl) were below the threshold of 50 mm/dL.²⁵ Triglyceride and fasting glucose levels were within optimal ranges for most participants.²⁵ This finding mirrors national trends showing AA women are less likely to demonstrate elevated levels of these two factors than other measures of cardiometabolic risk (i.e., blood pressure, HDL-cholesterol, LDL-cholesterol).²⁶ According to ATP-III criteria, 67.2% of participants were classified as having metabolic syndrome. This prevalence is over 3 times the national average for AA women (21%) based on the most recent NHANES data available.²⁶

Cardiorespiratory fitness levels of participants were low (M VO₂ peak=18.7 ml/kg/min). However, the values were comparable to those seen in other studies assessing fitness among similar populations of insufficiently active AA women at risk for cardiometabolic diseases.^27,28 The average fitness level for our participants was 41% lower than the normative reference value (M VO₂ peak=31.3 ml/kg/min) for our sample’s corresponding age group (30-39 years), as established by the Fitness Registry and Importance of Exercise National Databased (FRIEND) study.²⁹ Given cardiorespiratory fitness has emerged as a more powerful predictor of cardiovascular events and mortality risk when compared to traditional risk factors (i.e., hypertension, obesity, serum and blood measures of cardiometabolic risk),⁵ the low cardiorespiratory fitness levels of our sample suggest an important area for intervention. Pulse wave velocity assessments revealed a mean value of 7.4 m/s, which mirrors normative values for adult women aged 30-39 years with hypertension (i.e., 7.3 m/s).³⁰ However, it is still substantially higher than values typically observed among adults aged 30-39 without hypertension (i.e., 6.5 m/s); indicating premature age-related stiffening of the heart and increased risk cardiovascular disease and cardiovascular events. Given few studies have assessed pulse wave velocity among AA women, this outcome provides preliminary data on the impact of both obesity and low PA levels on this measure in this defined population.

Accelerometer-measured MVPA (1- and 10-minute bouts) showed moderate-to-strong associations with BMI, waist circumference, and cardiorespiratory fitness. Associations between accelerometer-measured MVPA and other measures of cardiometabolic risk were generally weak, as were associations between self-reported MVPA and all measures of cardiometabolic disease risk. Given our relatively small and homogeneous sample of insufficiently active women with obesity, these exploratory analyses had low statistical power, which was further diminished through adjustment for multiple testing. Accordingly, these findings should be interpreted with caution.

Taken altogether, the cardiometabolic disease risk profiles of our sample confirm that AA women who are both insufficiently active and with obesity are at elevated risk for developing cardiometabolic diseases. Results also emphasize the need for researchers to include more novel and prognostic measures of cardiometabolic disease risk when studying the health of AA women, including cardiorespiratory fitness and pulse wave velocity. Strengths of this study include using subjective and objective measures of PA and a comprehensive battery of cardiometabolic disease risk outcomes. Potential limitations include a relatively small sample size and the use of wrist-worn accelerometer protocol, which limited direct comparison of our accelerometer-measured PA outcomes to PA levels previously reported by nationally representative and large cohort studies (i.e., these studies have utilized waist-worn accelerometer protocols). We selected a non-dominant wrist-worn accelerometer protocol because we anticipated it would allow us to compare our accelerometer-measured MVPA outcomes to wrist-worn accelerometer data collected by NHANES starting with the 2011-2012 and 2013-2014 cycles. However, NHANES has yet to publish MVPA estimates based on wrist worn accelerometer data collection, nor provided guidance on how they intended to analyze their data to assess MVPA. This led to us use the only publicly available MVPA cutpoints¹⁶ for non-dominant wrist worn accelerometer data; which were developed using a convenience sample of healthy and normal weight Norwegian adults (M BMI=24 kg/m²; M age=34 years; n=17 women and n=13 men). Thus, the generalizability of these accelerometer-derived MVPA cutpoints to our sample of insufficiently active AA women with obesity and limited history of being physically active should be interpreted with caution.

Conclusions

The purpose of this article is to report baseline cardiometabolic disease risk factors of insufficiently active AA women with obesity enrolled in a culturally tailored physical activity intervention designed to increase PA and reduce cardiometabolic disease risk. Results suggest that AA women with obesity who are also insufficiently active are at elevated risk for adverse cardiometabolic health outcomes.

What’s New.

• Participants self-reported performing 30 minutes/week of moderate-to-vigorous physical activity. Accelerometer-measured outcomes showed our sample performed an average 15 minutes/day (or approximately 105 minutes/week) of moderate-to-vigorous physical activity when performed in bouts 1-minute or greater. However, when considering activity performed in bouts of at least 10-minutes, participants averaged 2 minutes/day (or approximately 15 minutes/week) of moderate-to-vigorous physical activity.

• Eighty-seven percent (n=52) of participants had elevated blood pressure, with most being classified as classified as having either Stage 1 (47.6%) or Stage 2 (28.3%) hypertension. Sixty-seven percent (n=39) were classified as having metabolic syndrome. Cardiorespiratory fitness levels were 41% lower than age-based normative reference values, while pulse wave velocity outcomes indicated elevated arterial stiffness.

• Results highlight that insufficiently active African American women with obesity are at elevated risk cardiometabolic diseases, as evidenced by both traditional and novel measures of cardiometabolic disease risk.