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Nigerian Journal of Physiological Sciences
Physiological Society of Nigeria
ISSN: 0794-859X
Vol. 22, Num. 1-2, 2007, pp. 37-42
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Nigerian
Journal of Physiological Sciences, Vol. 22, No. 1-2, 2007, pp. 37-42
Hypertension,
and Blood Pressure Response to Graded Exercise in Young Obese and Non- Athletic
Nigerian University Students.
K. Ibhazehiebo, U. Dimkpa1 and V. I. Iyawe
Department of Physiology, College of Medical Sciences,
University of Benin, Benin City Edo State, Nigeria, E-mail: viyawe@ yahoo.com.
1 Department of Physiology, College of Health Sciences, Igbinedion University, Okada, Edo State, Nigeria
Received: 15/2/2007
Accepted: 27/4/2007
Code Number: np07006
Summary
Hypertension, and
the effect of graded exercise on Blood pressure (BP), in 60 obese non-athletic
young medical students (40 females and 20 males) with Body Mass Index (BMI)
greater than 30 were studied. The subjects were in the age range of 18-22 years
with mean age of 20.30±1.32 years.
Twenty percent of the males and 7 percent of the females were found to be
hypertensives (P<0.05) and the severity of the hypertension significantly
(P< 0.05) increased linearly with increase in BMI (r =0.6). Our study
reveals a positive direct correlation between obesity and socioeconomic status
and BP. Marked increases in systolic blood pressure (SBP), diastolic blood
pressure (DBP), mean arterial pressure (MAP), time of return (RT) were observed
in the obese individuals compared to control at all levels of graded exercise
with the highest rises seen during severe exercise. Among the obese subjects,
the increases in BP were more in the males than females, but time of return was
higher in females than males. This study further confirms that obese young
individuals are prone to early onset of hypertension and thus other
cardiovascular diseases and less tolerant to physical exercises. Our results
add to the evidence that hypertension is common among obese young adults.
Key Words: BMI,
Hypertension, Exercise, mean arterial pressure
Introduction
Obesity is
defined as a BMI of >95th percentile for age and gender
(Stamler et al 1978, Cassono et al 1990). Young adults with a BMI
between the 85th to 95th percentile for age and gender
are defined as being at risk of obesity (Julius et al 2000). Individuals
with BMI less than 19.0 are underweight, BMI 19.0 to 25.0 are normal, BMI 26.0
to 30.0 are considered as over-weight and BMI of greater than 30.0 are
considered as obese (Barlow et al 1998). Adolescent and young adult
obesity is now a significant public health concern because of it`s immediate
impact on their physical and psychological health such as loss of confidence
and self esteem often leading to isolation and depression. More importantly, it
is a risk factor for the development of chronic diseases later in life.(Dietz,
1998).Recent studies have shown a significant increase in the prevalence of
obesity in adolescents and young adults in America and in the United Kingdom
(Van Itallie 1997, Dietz 1998), and the cost of obesity and its associated
illnesses is also increasing (Wang and Dietz 2002).
Indeed, the
prevalence of obesity increased in all ages, genders and ethnic/racial groups
during the past three decades being most prevalent in Hispanic males (27.5%)
and African American females (26.6%), adolescent and young adults (Ogden et
al 2002).The number of factors responsible for this condition ranges from
genetic factors (Rosenbaum and Liebel 1998), environmental factors such as
increased calorie intake and decreased physical activity (Birch and Fisher,
1998), psychological disorders (Barlow and Dietz, 1998) and endocrine and
genetic syndromes (Greger and Edwin 2001). Obese young adults do less physical
activities, prefer sedentary lifestyles and are less tolerant to physical
exercises. These attitudes ultimately increase their predisposition to
hypertension and other cardiovascular diseases later in life due to continuous
deposition of fatty adipose tissue and quickened atherosclerotic changes in
different blood vessels in their body (Hirsch et al 1976).
Also, a decreased cardiac, vascular, glucose and
phosphate response to B-agonist is found in obese individuals (Kannel et al
1979) and this further reduces their ability to dissipate excess calories and
reduces their susceptibility to hypertension. In Edo state, Nigeria, though no published data are available, every day contact with obese adolescents
and young adults of high socioeconomic status suggests an increase in the
prevalence of obesity amongst this age group and class. This correlates
positively with the Westernization of diet and rapid emergence of fast food and
confectionaries which are highly patronized by young adults especially of the
higher socioeconomic group. Hence the need for this study which will provide
baseline data for our environment.
Materials and Method
Sixty obese
subjects (20 males and 40 females) in the age range 18-22 years were selected
from among the 400 medical students of Igbinedion University Okada (a private
University mainly for the affluents) using the cluster sampling method. The
body mass index, that is weight in kilograms divided by height in meters
squared (Kg/m2) was used to determine obesity. Weight was measured
with light clothes on using a calibrated beam scale placed on a firm surface
and height measured using a meter rule. BMI greater than 30 was chosen as
obese.
Informed
consent was obtained, after which a structured health and lifestyle
questionnaire was administered to obtain information on general lifestyle,
eating habit and health status. Subjects with known history of hypertension or
any cardio-respiratory diseases, Diabetes Mellitus, pregnant females, smokers,
athletes, alcoholics and those on medication known to affect cardiovascular
function were excluded. An age and sex-matched control group of 60 subjects (20
males and 40 females) with BMI between 19 and 24 was employed in this study.
The blood pressure for each subject was measured using the auscultatory method.
A standard mercury column sphygmomanometer was used. All measurements were done
in the seated position with cuff tied around the left arm. The procedure was
usually done in the morning between 9 am and 12 noon. BP was expressed as mean
SBP ±SD mmHg and mean DBP± SD mmHg.
Following a standardized protocol, two separate measurements of
BP at rest were made at 15 minutes interval and the average of the two
measurements recorded. Where high blood pressure was recorded for the first
time, it was re-checked more than twice and the average of two close readings
was taken. To confirm the increase in BP, this procedure was repeated after a
week and the average of both readings was finally taken and recorded as the
systolic and diastolic blood pressures. Graded exercises were performed in a
quiet well -ventilated room (29°C).
Subjects were instructed not to consume any beverage containing alcohol or
coffee prior to exercise and BPmeasurements. After 10 minutes of quiet rest,
the subject's pre -exercise systolic and diastolic blood pressures were
re-measured to check for consistency with previously taken resting values. The
subjects were asked to perform exercise on a cycle ergometer for 5 minutes at a
rate of 5-10 cycles per minute (mild exercise). The systolic and diastolic
blood pressures were measured and monitored until it returned to pre- exercise
values and the time taken to return to pre- exercise values was recorded for
each subject. After resting for at least 30 minutes, the subjects exercise at 20-25
cycles per minute for 5 minutes (moderate exercise) and later 30-40 cycles per
minute for 5 minutes (severe exercise) still observing the 30 minutes quiet
rest in between the exercises and the times taken for the blood pressure to
return to pre- exercise values were recorded. Only 60 of the initial 70 obese
subjects recruited completed the study. The other 10 subjects could not
complete the severe aspect of the graded exercise and thus were not included in
the final analysis.
For the
purpose of this study, SBP greater than 140mmHg and DBP greater than 90mmHg was
regarded as hypertension. Data were analyzed using the student t-test and chi
square and expressed as mean ± S.D.
Statistical significance was set at P<0.05. A correlation analysis was used
to establish a relationship between BMI and BP.
From the analysis of the questionnaire, in 56% of
the obese subjects, the obesity was probably genetic since one or both
parents were fat. 75% of the subjects did not exercise at all, while 25%
exercised occasionally. All the subjects had at one stage of their lives been
psychologically traumatized because of their obese condition. 100% of the
subjects had the knowledge that obesity could be deleterious to their health
and would welcome any intervention to help lose weight.
Seven out of the 60 obese subjects (12%) were
hypertensive (p<0.05). They had a mean BMI of 32.45±1.1 Kg/m2, mean SBP of 158.26 ±10 mmHg and mean DBP of 96.5± 9 mmHg. Unlike the obese subjects, there
was no incidence of hypertension in the control subjects. 5 of the 7 obese
subjects with hypertension (70%) had episodes of un-explained headache and
dizziness, while the other 2(30%) had episodes of unprovoked epistaxis.70% of
all obese subjects admitted that they consistently fed on high calorie diet
mainly snacks, fizzy sugary drinks and confectionaries- the so called junk
food. All obese subjects with hypertension were in this category.
Table 1: Pre-exercise blood pressure of obese subjects.
SEX |
Age (yr) |
No |
Height (m) |
Weight (Kg) |
BMI (Kg/m2) |
SBP (mmHg) |
DBP (mmHg) |
MAP (mmHg) |
Males |
20.3± 1.3 |
20 |
1.7±1.0 |
91.1±1.6
|
31.8±1.3 |
137.4±11 |
82.6±12 |
100.8±13 |
Females |
19.3±1.4 |
40 |
1.6±1.1 |
85.0±2.4
|
32.0±1.1 |
126.8±10 |
79.4±12 |
93.3±12 |
Table 2 : Pre-Exercise Blood
Pressure Of Control Group
Sex
|
Age
(Years)
|
No |
HT
(Meters)
|
WT
(KG)
|
BMI
Kg/m2
|
SBP
(mmHg)
|
DBP
(mmHg)
|
MAP
(mmHg)
|
Males
|
20.2±1.4 |
20 |
1.7±0.2 |
63.8±3.0 |
21.3±0.9 |
119.4±8.9 |
70.6±5.9 |
84.2±5.2 |
Females
|
19.3±1.2 |
40 |
1.65±0.8 |
56.8±8.0 |
21.9±2.8 |
110.1±11.0 |
69.4±7.6 |
80.6±8.2 |
Table 3: Blood pressure changes
in obese subjects following graded exercise.
SEX |
SBP
(mmHg)
|
DBP|
(mmHg)
|
MAP
(mmHg)
|
RT
(Mins)
|
Degree of Exercise
|
Males |
156.3±14.0 |
87.9±10.0 |
110.2±12.0 |
5.97±1.2 |
Mild |
Females |
141.0±9.0 |
86.4±10.1 |
107.3±8.0 |
7.4±1.4 |
Mild |
Males |
163.4±10.0 |
93.6±7.0 |
119.3±10.0 |
8.0±1.0 |
Moderate |
Females |
152.3±11.0 |
92.0±6.0 |
114.3±9.0 |
9.3±1.4 |
Moderate |
Males |
173.1±14.0 |
98.5±10.0 |
124.2±12.0 |
11.2±1.3 |
Severe |
Females |
163.1±9.0 |
95.4±10.0 |
118.8±7.0 |
13.1±1.9 |
Severe |
Results from Table 1 show the pre-exercise values of
SBP, DBP, MAP to be 137.4±11, 82.6± 12 and 100.8±
13mmHg in obese males and 126.8± 10,
79.4± 12, and 93.4± 13mmHg in obese females and this is higher
than in control SBP, DBP, MAP i.e. 119.4±9,
70.6 ±6, 84.2± 5 mmHg in non- obese males and 110.1± 11., 69.4± 8, 80.6± 8mmHg in non obese females respectively
(Table 2).
Following
graded exercise, there was a marked increase in SBP, DBP, and MAP in obese
subjects as the intensity of the exercise increased from mild to severe i.e.
from 156.3 ±14, 87.9± 10, 110.2±
12mmHg SBP, DBP, and MAP respectively, to 173.1±
14, 98.5± 9, 124.2± 13 mmHg in obese males; and 141.0±9, 86.4 ±10,
107.3± 8mmHg to 163.1± 9, 95.4±
10, and 118.8± 7mmHg in obese females.
In the control only modest increases were noticed, SBP, DBP and MAP values from
133.0± 7., 70.1± 7.9 and 95.9±9mmHg to 153.0±13,
89.2± 12 and109.5± 9mmHg in non- obese males; and 134.5±11, 74.6±4,
94.6± 5mmHg to 148.8± 12, 85.8±
11 and 106.7± 9mmHg in non- obese
females (Tables 3 and 4).
Also the time
in minutes taken for the blood pressure to return to pre-exercise levels was
considerably longer in obese subjects compared to control subjects in all the
categories of graded exercises. In the obese group, it was longer in females
than in males i.e. 5.97 ±1.21, 7.9± 1.01, 11.21±
1.34 minutes in obese males following mild, moderate and severe exercises and
7.36± 1.41, 9.31± 1.40, 13.14±1.92
minutes in obese females following same graded exercise (Table 3) .The time was
shorter in control subjects i.e. 4.40±
1.31, 6.93± 2.16, 9.44± 2.37 minutes in non- obese males and 5.43± 1.49, 8.50±
1.44, 11.6 ±1.73 minutes in non-obese
females (p<0.05) Table 4.
The increases
in BP following exercise in the obese when compared with the non-obese subjects
are shown in Tables 5A and 5B. The increases were highly significant for SBP (P
< 0.01). When male obese were compared with the female obese subjects, SBP
also increased more significantly following exercise in the males than
females-Table 6A and 6B.
Table 4: Blood pressure changes in control subjects
following graded exercise.
Sex |
SBP
(mmHg)
|
DBP
(mmHg)
|
MAP
(mmHg)
|
RT
(Mins)
|
Degree of Exercise
|
Males |
135.0±7.4 |
70.1±7.4 |
95.9±9.2 |
4.4±1.3 |
Mild |
Females |
134.5±10.5 |
74.6±4.2 |
94.6±5.1 |
5.4±1.5 |
Mild |
Males |
148.2±14.8 |
84.6±12.4 |
105.7±10.9 |
6.9±2.2 |
Moderate |
Females |
140.3±11.6 |
78.3±9.2 |
101.3±7.6 |
8.5±1.4 |
Moderate |
Males |
153.0±13.1 |
89.2±11.5 |
109.5±9.4 |
9.4±2.4 |
Severe |
Females |
148.8±11.8 |
85.8±10.9 |
106.7±9.1 |
11.6±1.7 |
Severe |
Table 5a: Changes in SBP in obese and non- obese
subjects. SBP(mmHg)
Degree of Exercise
|
Obese |
Non Obese
|
Significance |
Mild |
150.4±10.3
|
94.3 ± 8.6
|
P < 0.01 |
Moderate |
161.7±9.6
|
113.8 ± 10.1 |
P < 0.01 |
Severe |
169.4±11.2
|
126.0 ± 10.8 |
P < 0.01 |
Table 5b: Changes in DBP in obese versus non-obese
subjects. DBP(mmHg)
Degree of Exercise
|
Obese |
Non Obese |
Significance |
Mild |
85.4±8.6
|
78.3 ± 9.4 |
NS |
Moderate |
91.7 ±6.0
|
83.9 ± 7.5 |
NS |
Severe |
97.4±8.9
|
89.3 ± 9.2 |
NS |
Discussion
Obesity in young
adults has become a significant public health problem because of its impact on
the physical and psychological health and because it is a risk factor in the
development of chronic cardiovascular and metabolic diseases later in life
(Stamler et al 1978, Cassono et al 1990, Julius et al
2000.).
Blood pressure
elevation may be the intermediate phenotype of an underlying sympathetic over
activity in hypertension where stimulation of B-adrenergic receptors increases
the total body energy expenditure. A chronic increase in the sympathetic tone
causes down regulation of B-adrenergic receptors leading to a decreased
cardiac, vascular, glucose and phosphate responses.(Julius et al 2000).
This suggests that obesity is linked with hypertension through the sympathoadrenal
system. (Landsberg 1986).
Our result
indicates that the prevalence of obesity among young adults (18-22 years age
range) is 15% (i.e. 60 of the 400 subjects) This agrees with Ogden et al 2002
who reported the prevalence of obesity in adolescent and young adults to be
15%. From our study, the occurrence of hypertension among the obese young
adults was 12% and this is in line with Bertsias et al 2003 who reported
similar levels of prevalence among medical students in Crete, Greece. From this
study, the increase in BP was more in obese males than females. The SBP, DBP,
MAP of hypertensive obese male subjects were higher than those of their female
counterparts .The male: female ratio for the development of hypertension among
obese young adults was 3:1 as 20% of the obese males had hypertension compared
to 7% of the obese females.
Table 6a; Changes In SBP In
Obese Males Versus Obese Females
SBP(mmHg)
Degree of Exercise
|
Male |
Female |
Significance |
Mild |
156.3±14.0
|
141.0 ±9.0
|
P <0.05 |
Moderate |
163.4±10.0
|
152.3±11.0
|
P <0.05 |
Severe |
173.1±14.0
|
163.1±9.0
|
P <0.05 |
Table 6b: Changes in DBP in obese males versus obese
females.
DBP(mmHg)
Degree of Exercise
|
Male |
Female |
Significance |
Mild |
87.0±10.0
|
86.4±10.1
|
NS |
Moderate |
93.6±7.0
|
92.0±6.0
|
NS |
Severe |
98.5±10.0
|
95.4±10.0
|
NS |
Though genetic factors play a very significant role
in the development of obesity, environmental factors seem to be the most
plausible explanation for the increased prevalence of obesity among adolescents
and young adults in our study in a university campus where 70% of the obese
subjects consistently fed on high calorie foods, such as fast food and
confectionaries which are readily available, and heavily promoted among this
age group. Also exercise and physical activities are no longer part of regular
young adults everyday life as some never walk or cycle to school, or play any
kind of sport. It is not unusual for adolescents and young adults to spend
hours in front of the television or computer. This is evident from our study
where 75%(45) of our obese subject dont exercise at all while only a mere 25%
(15) occasionally involve themselves in exercise. Our study also shows that
there is a direct relationship between obesity and family income since all the
obese subjects were from wealthy affluent homes compared to our control group
where most of the subjects were from average or outright poor homes. This
contrasts with the findings of Trioano and Flegal 1998 who reported an inverse
relationship between obesity and family income in non-Hispanic white
adolescents.
The present study indicates that
blood pressure parameters rise to higher levels in obese adolescents and young
adults under conditions of graded exercise compared with non-obese adolescents
and young adults. This finding is consistent with those of Dempsay et al,
1966, Lampman et al 1985, Segal et al 1989, and Shephard et al
1994. SBP is labile and changes more rapidly during exercise and this may
explain the significant difference SBP between obese and non-obese subjects as
opposed to DBP, which is slow to respond to exercise. The obese were more
stressed by the graded exercises than the non- obese; in other words, the
exercise tolerance levels of the obese young adults were considerably lower
compared to control. Whereas all the control subjects were able to complete
the various levels of graded exercise, only 60 of the 70 initial obese subjects
could complete the graded exercises. Comparing male and female obese subjects,
exercise tolerance was lower in obese females than their male counterpart as 9
of the 10 obese subjects who could not complete the graded exercise were
females and this correlates with previous works done by Foss et al 1975,
Lampman et al 1987, Sakamoto et al 1993, Shephard et al
1994. Also, the time to return to pre-exercise levels was longer in the
females.
Conclusion
Obesity is associated with premature increase in BP. A
significant number of young obese adults in this study were hypertensive, a
situation that would predispose them to cardiovascular complications and other
health problems in future. The early increase in BP is a result of interwoven
genetic and environmental factors. Also, the time of return of BP parameters to
baseline values was longer in obese adolescents and young adults than non-obese
adolescents and young adults following graded exercise. Our results underscores
the need to perform large scale epidermiologic studies within the general
Nigerian young adult population, and implement health promotion programmes for
them.
References
- Barlow, S. E., Dietz, W. H. (1998). Obesity evaluation and treatment:
expert committee recommendations. Pediatrics. 102: E29.
- Bertsias,
G. (2003).Overweight and obesity in relation to cardiovascular disease risk
factors among medical students in Crete, Greece. BMC Public Health. 3(1) 3-12
- Birch, L. L., Fisher, J. O. (1998). Development of eating behaviours
among adolescents. Pediatrics. 101:539-549.
- Cassono, P. A. (1990). Body fat distribution, blood pressure, and
hypertension: a prospective cohort study of men in the normative aging study. Ann
Epidemiol. 1:33-48.
- Demsey, J. A. (1960). Work capacity determinants and physiologic cost
of weight-supported work in obesity. Journal of Applied Physiology. 15:
377-392
- Dietz, W. H. (1998). Health consequences of obesity in youth:
childhood and predictors of adult disease. Pediatrics. 101:503-525.
- Foss, M. L., Lampman, R. M., Watt, E. (1975). Initial work tolerance
of extremely obese patients. Archives of Physical Medicine and
Rehabilitation. 56: 63-67.
- Hirsch, J.
L., Batchelor, B. (1976) . Adipose tissue cellularity and human obesity. Clinical
Endocrinology and Metabolism. 5: 299-315.
- Iyawe, V. I., Ighoroje, A. D. A., Iyawe, H. O. (1996). Changes in
blood pressure and serum cholesterol following exercise training in Nigerian
hypertensive subjects. J. Human Hypertension, 10(7) ; 483-487.
- Julius S, Valentini, M., Palatini, P. (2000). Overweight and
hypertension; a 2-way street?. Hypertension. 35: 807-825.
- Kannal, W. B., Gordon, T., Castelli, W. P. (1979). Obesity, Lipids,
and glucose intolerance. The Framingham study. American Journal of Clinical
Nutrition. 32:1238-1256.
- Lampman, R. M., Schteingart, D. E., Henry, G. C. (1987). Medical
management of severe obesity: Graded exercise testing. Journal of
Cardiopulmonary Rehabilitation. 7 : 358-364.
- Must, A., Strauss, R.
S. (1999). Risks and consequences of childhood and adolescent obesity. The
International Journal of Obesity 23:S2-S11.
- Ogden, C. L. (2002). Prevalence and trends in overweight among US
children and adolescents, 1999-2000. Journal of the American Medical
Association 288:1728-1732.
- Rosenbaun, M., Liebel, R. (1998). Pathophysiology of childhood
obesity. Advance Pediatrics. 35:73-137.
- Sakamoto, S., (1993). The effect of obesity on ventilatory response
and anaerobic threshold during exercise. Journal of Medical Systems. 17
(3-4) : 227-231.
- Segal, K. R., Pi Sunyer, F. X. (1993) Exercise and obesity. Medical
Clinics of North America. 73 (1): 217-236
- Shephard, R. J., Bouchard, C. (1999). Principal components of
fitness: relationship to physical activity and lifestyle. Canadian Journal
of Applied Physiology. 19 (2) : 200- 214.
- Sowers, J. R. (2003). Obesity as a cardiovascular risk factor. Am.
J. Med. 115 Suppl 8 A: 37S-41S.
- Stamler, R. (1978). Weight and blood pressure:
findings in hypertension screening of 1 million Americans. JAMA. 240:
1607-1610.
- Troiano, R. P., Flegal, K. M. (1998). Overweight children and
adolescents: description, epidermiology and demographics. Pediatrics. 101: 497-504.
- Wang, G., Dietz, W. H. (2002). Economic burden of obesity in youths
aged 6 to 17 years: 979-1999. Pediatrics. 109: 81-87.
©Physiological Society of Nigeria, 2007
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