Association of fitness and waist circumference with hypertension in Brazilian elderly women

Abstracts

FUNDAMENTO: O efeito protetor da aptidão cardiorrespiratória tem sido reconhecido nos adultos. Entretanto, essa relação ainda não se mostra esclarecida nos idosos. OBJETIVO: Analisar a associação entre hipertensão e aptidão cardiorrespiratória (ACR) em 1.064 mulheres idosas Brasileiras. MÉTODO: A obesidade central foi estimada pela circunferência abdominal (CA) e a ACR pelo teste de caminhada de 6 minutos. Os testes de ANOVA one-way, Qui-quadrado e regressão logística foram usados para a análise estatística. RESULTADOS: A prevalência de hipertensão foi de 53,9%. O grupo obesidade central apresentou maior risco para hipertensão quando comparado ao grupo não-obesidade central, mesmo pertencendo ao mesmo nível de ACR. Além disso, ambos os grupos mostraram um aumento progressivo do risco para hipertensão do maior para o menor grupo de ACR, indicando uma relação inversa entre ACR e obesidade central. O grupo não-obesidade central obteve o menor odds ratio (OR) de 1,49 (95%IC 0,97-2,28) e 1,54 (95%IC 0,94-2,51); enquanto que no grupo obesidade central, o OR foi 2,08 (95%IC 1,47-2,93), 2,79 (95%IC 1,79-4,33) e 3,09 (95%IC 1,86-5,12). CONCLUSÃO: Os resultados encontrados indicaram que a CC é um forte preditor de hipertensão, e que o efeito protetor da ACR pode ser estendido às mulheres idosas, mesmo àquelas com obesidade central.

Obesidade; aptidão física; idoso; pressão arterial; prevenção de doenças; circunferência abdominal; mulheres; Brasil

FUNDAMENTO: El efecto protector de la aptitud cardiorrespiratoria ha sido reconocido en los adultos. Sin embargo, esa relación todavía no está aclarada en las personas adultas mayores. OBJETIVO: Analizar la asociación entre hipertensión y aptitud cardiorrespiratoria (ACR) en 1.064 mujeres adultas mayores brasileñas. MÉTODOS: La obesidad central se estimó por la circunferencia abdominal (CA) y la ACR por el test de marcha de 6 minutos. Se emplearon las pruebas de ANOVA one-way, Chi-cuadrado y regresión logística para el análisis estadístico. RESULTADOS: La prevalencia de hipertensión fue de un 53,9%. El grupo obesidad central presentó mayor riesgo para hipertensión cuando comparado al grupo no-obesidad central, aun perteneciendo al mismo nivel de ACR. Además de ello, ambos grupos revelaron un aumento progresivo del riesgo para hipertensión del mayor para el menor grupo de ACR, indicando una relación inversa entre ACR y obesidad central. El grupo no-obesidad central obtuvo el menor odds ratio (OR) de 1,49 (95%IC 0,97-2,28) y 1,54 (95%IC 0,94-2,51); mientras que en el grupo obesidad central, el OR fue 2,08 (95%IC 1,47-2,93), 2,79 (95%IC 1,79-4,33) y 3,09 (95%IC 1,86-5,12). CONCLUSIÓN: Los resultados encontrados indicaron que la CC es un fuerte predictor de hipertensión, y que el efecto protector de la ACR puede extenderse a las mujeres adultas mayores, aun a las con obesidad central.

Obesidad; aptitud física; adulto mayor; presión arterial; prevención de enfermedad; circunferencia abdominal; mujeres; Brasil

ORIGINAL ARTICLE

^IUniversidade de Pittsburgh, PA, Estados Unidos

^IIUniversidade Federal do Paraná, Curitiba, PR - Brazil

^IIIHospital Universitário Evangélico de Curitiba, Curitiba, PR - Brazil

Mailing address

SUMMARY

BACKGROUND: The protective effect of cardiorespiratory fitness, regardless of obesity, has been recognized in adults. However, this association is still not clear in elderly individuals.

OBJECTIVE: To analyze the association between hypertension and cardiorespiratory fitness in 1,064 elderly Brazilian women.

METHODS: Central obesity was estimated by waist circumference and cardiorespiratory fitness by the 6-minutes walk test. ANOVA one way, chi-square and logistic regression were used for the statistical analysis.

RESULTS: The prevalence of hypertension was 53.9%. The central obesity group had higher odds for hypertension when compared with the non-central-obesity group, in the same cardiorespiratory fitness group. Furthermore, both the central obesity and non-central obesity groups had a progressive increase in the odds ratio for hypertension, from the highest to lowest fitness groups, indicating an inverse relation between fitness and central adiposity. The non-central obesity group had the lowest odds ratios (OR), 1.49 (95%IC 0.97-2.28) and 1.54 (95%IC 0.94-2.51); whereas the central obesity group had an OR of 2.08 (95%IC 1.47-2.93), 2.79 (95%IC 1.79-4.33) and 3.09 (95%IC 1.86-5.12).

CONCLUSION: Our findings indicated that the waist circumference measurement is a strong predictor of hypertension and suggested that the protective effect of cardiorespiratory fitness can be extended to elderly women, even to those with central obesity.

Key words: Obesity; physical fitness; aged; blood pressure; disease prevention; abdominal circumference; women; Brazil.

Introduction

Hypertension has a high prevalence in adults, tending to affect more women than men all over the world. It is well recognized that its prevalence is increasing gradually with advancing age, affecting approximately half of the elderly Brazilian people^1-7.

One of the main factors related to the genesis of hypertension is an increase in the adipose tissue, which currently has been defined as "obesity hypertension". Although central obesity has been shown to alter the cardiovascular, renal, and metabolic systems, triggering inflammatory responses, the cause-effect relationship between adiposity and hypertension is not quite understood. However, it is common agreement that individuals with elevated central adiposity have an increase in the risk for hypertension, cardiovascular disease and mortality^3,6,8-12. Additionally, central obesity has been strongly associated with a high prevalence of hypertension^6,8-10,12-20.

According to the findings from the MONICA study, a 2.5 cm increase in waist circumference (WC) for women corresponds to an increase in systolic blood pressure of 1mmHg⁶. Furthermore, the JNC 7³ have reported that the relationship between blood pressure and risk of CVD is continuous, consistent and independent of other risk factors; thus, it is suggested that hypertensive individuals become more vulnerable to acquire other health problems, particularly elderly individuals who have been suffering the time-accumulated deleterious effect of aging and cumulative time exposure of risk factors for longer periods of time^1,2,6.

This scenario has become a crescent concern for public health professionals, and primary prevention has been the main focus, which includes weight loss, balanced diet control, changes in alcohol and smoking habits and especially, exercise practice^{1-3,7,13,15,18,21}. In spite of the JNC 7³ and the V Brazilian Recommendations for Hypertension⁵ advice, as a lifestyle modification, that all individuals (hypertensive or not) engage in regular aerobic physical activity due to the protective effect of high fitness in relation to health risks and mortality in adults, even with excess of adiposity, this tendency has been less explored in elderly women^1,22-30. For this reason, the main purpose of this study was to determine the association between hypertension and cardiorespiratory fitness (CRF), and to examine the joint effect of the CRF and central obesity with hypertension in elderly Brazilian women.

Methods

Design

The present study was carried out in the city of Curitiba, state of Parana, Brazil. The sample consisted of elderly women that participated in community groups in the entire city. These groups were randomly selected. Subjects were invited to participate in this investigation after receiving a detailed clarification of the procedures involved in this research, including benefits and possible risks. All subjects signed the informed consent form, indicating that their participation was voluntary.

One thousands and sixty-four non-institutionalized women, aged between 60.0 - 88.8 years, agreed to participate in the study. The sample consisted predominantly of Caucasian subjects, classified as of low or middle socio-economic level.

All the assessments were performed between 08:00 and 10:00 am, to avoid the influence of circadian variations. Furthermore, the participants were instructed not to ingest any food two hours before the tests, as well as to avoid any vigorous physical activity for 24 hours before testing. The assessments were carried out at the Physiology Laboratory of the Exercise and Sports Research Center of the Universidade Federal do Parana.

The study protocol was approved by the Ethics Committee of the Universidade Federal do Parana, according to the norms established in the Resolution 196/96 of the National Health Council, concerning researches involving human subjects.

Measurements

Blood pressure was measured according to JNC 7³ recommendations, using the auscultatory method by a trained physician who made sure that the subjects were comfortably seated for at least five minutes on a chair (with feet placed on the floor), in a quiet environment, and with their right arm supported at heart level. Hypertension was determined when the systolic blood pressure was > 140 mmHg and diastolic blood pressure > 90 mmHg or when the subject self-reported the current use of antihypertensive medication. In addition, the subjects were asked if their physician had ever told them that they were hypertensive.

Waist circumference (WC) was measured according to the procedures by Lohman et al³¹. In order to avoid inter-examiner variability, this measurement was performed by only one trained examiner for all participants.

The 6-min walk test (6MW) was administered to estimate cardiorespiratory fitness. The test was performed on a 54.4 m rectangular course (18.0 m length x 9.2 m width). The maximum distance walked in 6 minutes was recorded for each subject. The test was discontinued if, at any time, a participant showed signs of dizziness, pain, nausea, or undue fatigue³².

Additionally, participants reported family history of cardiovascular disease and smoking status (current smoker - CS or not). Socioeconomic status was determined by a validated national socioeconomic questionnaire.

Statistical analyses

The Kolmogorov Smirnov test of normality was used to determine that the distribution of the sample data was parametric. Subsequently, means, standard deviations and relative frequencies were calculated for the descriptive values according with blood pressure classification - normo/hypertensive. A one-way analyses of variance (ANOVA) was used to identify differences between age, socioeconomic status, systolic and diastolic blood pressure, waist circumference and cardiorespiratory fitness in the normo/hypertensive groups. The Chi-Square test was used to determine if frequencies of smoking status and family history of cardiovascular disease significantly differed between the normo/hypertensive groups.

Logistic regression analysis was used to determine the association between central adiposity (WC) and cardiorespiratory fitness (CRF) with hypertension. Hypertension was treated as a dichotomous variable (yes/no). WC and CRF were divided into quartiles at the univariate analysis. Odds Ratio (OR) and their 95% confidence intervals (95%CI) were calculated using age and adjusted-models, which included the potential confounders' variables - socioeconomic status, family history of cardiovascular disease and smoking status, and central adiposity or cardiorespiratory fitness. To investigate the joint effect of central adiposity and cardiorespiratory fitness with hypertension, the following variables were created: CRF > 490.2 and WC < 88.0 (referential group) and > 88.0 cm; CRF < 490.2 - > 431.0 and WC < 88.0 and > 88.0 cm; CRF < 431.0 - > 330.8 and WC < 88.0 and > 88.0 cm; CRF < 330.8 and WC < 88.0 and > 88.0 cm. The division of the groups provided the information from high to low CRF quartiles for the non-central (WC < 88.0) and central obesity (WC > 88.0 cm) groups. All analyses were performed using the Statistical Package for the Social Sciences (SPSS, version 13.0) for Windows.

Results

Of the 1,064 participants, 574 subjects were classified as hypertensive (53.9%). The one-way analysis of variance and chi-square analysis showed significant differences between normo/hypertensive groups for the following variables: age, socioeconomic status - SES, systolic blood pressure - SBP, diastolic blood pressure - DBP, waist circumference - WC, cardiorespiratory fitness - CRF, and family history of cardiovascular disease - FH_CVD. Smoking status - CS did not differ between groups (Table 1).

The highest prevalence of hypertension was found in the highest central adiposity group (WC >94.0 cm), indicating a direct association between these variables (Figure 1). In contrast, a trend of an inverse association was found between the prevalence of hypertension and CRF (Figure 2).

The logistic regression analysis determined a gradual increase in odds ratio (OR) across the WC quartiles. Table 2 indicates three-fold odds for hypertension for those women with higher central adiposity (WC >94.0 cm) regardless of age or confounder variables. However, after adjusted for CRF the odds was slightly attenuated, being around 5% for those with WC >94.0 cm and 8% for those with WC of 87 - 93.9cm. Table 3 shows the association between hypertension and CRF. The two highest CRF groups had a reduction of 33 and 36%, respectively, in the odds for hypertension. However, after including WC in the regression model, the odds ratio increased to 0.76 and 0.75 in the same two highest CRF groups, respectively.

Figure 3 shows a tendency that central obese elderly women (WC >88.0cm) had a higher odds for hypertension when compared with the non-central-obesity (WC <88.0cm), in the same CRF group. Therefore, the greater CRF the lower the odds for hypertension for non-central and central obesity group (WC>88.0cm).

Discussion

Excess of adiposity has been directly associated with the prevalence of hypertension, supporting our findings that showed that women with higher WC had an increase of three-fold in the odds ratio for hypertension, indicating that WC is a strong predictor of hypertension in this sample. Several investigations have shown that WC is an indicator of central obesity in adults and elderly women^{1,8-12,21,23,33}, consequently it is directly associated with health risks^17,18,34. Additionally, WC has a greater predictive cutoff point for hypertension than BMI in men¹⁹ and mainly in the first WC cutoff point (WC >80) in adult women¹⁴, WC has an odds ratio for hypertension of 1.76 between 80-88cm and OR 2.18 for WC >88cm¹³, and it is a strong predictor of CVD in women aged 25 to 74 years³⁴.

Despite the recognized importance to maintain moderate-high CRF, even in individuals with excess of adiposity^{23,25,27,35,36}, this approach seems to be yet little explored for elderly women. Our results verified that the CRF mean was higher in the normotensive than in the hypertensive group and indicated an inverse association between the prevalence of hypertension and CRF. These findings are supported by a recent investigation that examined the effects of CRF and incidence of hypertension in the Aerobic Center Longitudinal Study (ACLS), which was carried out in normotensive women without CVD at baseline. Those results indicated an inverse relation between CRF and hypertension after follow-up. Furthermore, at the multivariate model, the OR was 0.61 for a moderate fitness level and 0.35 for a high fitness level, indicating a strong protective effect of CRF. Similarly, our results of the univariate analysis indicated a decrease of 24 and 25% in the odds for hypertension in the two highest CRF quartiles, respectively, even after the WC measurement was included in the model. It seems that CRF has a protector effect in hypertension; the same effect was confirmed for women with prehypertension³³ and for elderly⁵. Hu et al¹⁶ also indicated a protective effect of the physical activity level (PAL) for hypertension in women aged 25 to 64 years.

Although the results of the previously presented studies were not specific for elderly women, being determined using a sample stratified by age groups³⁰, or adjusted by age^16,27,34, they still support our findings that CRF has a protective effect for hypertension, and consequently, this CRF effect can be extended specifically to elderly women, regardless of the non-central obesity or central obesity classification.

Similarly to what was reported by ACLS researchers²³ our purpose was not to minimize the effect of obesity on elderly women's health, but to confirm the benefits of the maintenance of CRF in this specific population. Currently, there is an increased concern about what strategy can be more efficient against hypertension, because it is supposed that even normotensive individuals, younger than 65 years, have a remaining lifetime risk of developing hypertension of approximately 90%. In addition, it seems that several cases of pharmacological treatment have not been effective in the control of this condition, mainly in older women^1,2. For these reasons, the primary prevention has been recognized as the most important one^3,5, such as regular practice of aerobic exercises, which has been highly recommended. The maintenance of a moderate-high CRF through aerobic exercise, mainly when performed since the adult age, seems to promote health benefits and to help sustain them for a long time^22,26.

Our findings have clinical and public health implications, supporting the premise that the protective effect of CRF over hypertension can be extended to elderly women, even to those with central obesity. It is suggested that health professionals should encourage their patients to increase physical activity levels, especially with aerobic exercises, as regular physical activity has been considered a common denominator for the clinical therapy of low fitness and excess of weight^5,23.

Although the self-reported hypertension was confirmed by actual measurements of blood pressure or by a previous medical diagnosis, this factor can be considered a limitation for our findings. Unfortunately, our survey did not include other risk factors for hypertension, such as alcohol consumption and dietary habits (i.e., sodium and potassium intake) to be used as adjustments in the regression analysis. CRF was determined using a submaximal exercise test, which could have over/underestimated our results. However, this test is considered a valid option to estimate CRF specifically in elderly subjects that were not recommended to be exposed to a maximal effort³⁷. Both non-central and central obesity groups with lower CRF had an insufficient number of participants (n=25 and 24, respectively) in our final regression analysis, not allowing consistent results to be drawn about these specific groups. However, the tendency found across all groups was significant. Considering that the design of this study is cross-sectional it is not possible to provide evidence for causality or the time effect on hypertension based on our results.

Potential Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Sources of Funding

There were no external funding sources for this study.

Study Association

This study is not associated with any post-graduation program.

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Association of fitness and waist circumference with hypertension in Brazilian elderly women

Maressa Priscila Krause^I; Tatiane Hallage^II; Mirnaluci Paulino Ribeiro Gama^III; Cristiane Petra Miculis^II; Nívea da Silva Matuda^II; Sergio G. da Silva^II

Publication Dates

• Publication in this collection
  13 Oct 2009
• Date of issue
  July 2009

History

• Reviewed
  11 June 2008
• Received
  20 May 2008
• Accepted
  19 June 2008