Download plasma insulin pattern in a hausa-fulani ethnic group in northern

Annals of African Medicine
Vol. 3, No. 1; 2004: 7 - 9
PLASMA INSULIN PATTERN IN A HAUSA-FULANI ETHNIC GROUP
IN NORTHERN NIGERIA
A. G. Bakari
Department of Medicine, Ahmadu Bello University Teaching Hospital, Zaria, Nigeria
Reprint Requests To: Dr. A.G. Bakari, Consultant Physician and Endocrinologist, Department of Medicine, A.
B. U. Teaching Hospital, Zaria, Nigeria. E-mail: [email protected].
Abstract
Background: Plasma insulin levels seem to play significant roles in health and disease; and prevailing plasma
insulin levels are modulated by racial and ethnic factors. There has been no previous study of the plasma insulin
pattern in any northern Nigerian tribe.
Methods: Thirty-six (24 males and 12 females) healthy volunteers of a northern Nigerian tribe were studied.
Fasting plasma insulin and glucose levels were estimated; this was followed by a standard OGTT to study the
plasma insulin response to oral glucose challenge.
Results: Although there were marked individual variations with 16.7% of individuals demonstrating fasting
hyperinsulinaemia, mean fasting plasma insulin levels were similar to those earlier reported elsewhere.
Conclusion: These findings are discussed in view of other factors known to modulate plasma insulin levels.
Key words: Plasma Insulin, northern Nigeria
Introduction
Insulin, the primary anabolic hormone of the human
body has been implicated in the aetiopathogenesis of
several non-communicable diseases like hypertension,
peripheral vascular disease, coronary heart disease and
even cancer. 1-4 There is evidence that the pattern of
fasting plasma insulin and plasma insulin response to
oral glucose challenge is modulated by racial and ethnic
factors, 5, 6 as well as such other factors as diet and
physical activity. 7 Although there are few studies on
plasma insulin levels in few ethnic groups in Nigeria, 810
there has been no study of plasma insulin levels in any
northern Nigerian ethnic group. The plasma insulin
response to a standard oral glucose tolerance test
(OGTT) in 36 healthy normoglycaemic individuals of
Hausa - Fulani ethnicity in Zaria, northern Nigeria was
studied.
Subjects and Methods
Zaria (located at Longitude 080 300 East and latitude 040
000 North of the equator) in Northern Nigeria is
inhabited mainly by two tribes. The Hausa and Fulani
(Fulbe); are two distinct tribes with similar cultural
practices. Intermarriage between these tribes occurs
quite frequently especially in urban areas of northern
Nigeria, making it difficult to come across a ‘pure’
breed of any of the tribes in most of the urban areas of
northern- Nigeria. The term Hausa-Fulani has therefore
been unofficially adopted and commonly used to refer to
the two groups or a hybrid of the two.
Hausa-Fulani volunteers were recruited after
community visits to explain the nature and aims of the
study. The exclusion criteria were: Clinical evidence of
any illness, personal or family history of diabetes or
hypertension, current use of any form of medication and
engagement in competitive sports.
Informed consent was obtained from all subjects;
this was followed by metabolic studies. After an
overnight ten to twelve hours fast, commencing between
21.00 to 22.00 hours the preceding night. 11 On the day
of the studies, Information on age, sex and
anthropometric measures were obtained from all
subjects. Weights (in Kg) were taken with only
undergarments to the nearest 0.5kg. Heights (in meters)
were taken to the nearest 0.5 cm with subjects standing
erect without shoes or headgear. Body Mass Index
(BMI) was derived by dividing body weight by the
square of the height BMI of >25 kgm-2 was considered
overweight. 12
Fasting venous blood samples were drawn from each
subject using 18 gauge needles fitted with plastic
canulae. The canulae were then kept patent by slow
infusions (3-5 drops per minute) of 0.9 percent saline
without any additive. The fasting blood samples were
promptly centrifuged and analyzed promptly for glucose
using a glucose oxidase method. 13 Aprotinin 200
KIUl/ml was added to part of the sample reserved for
insulin assay 14. These samples were immediately
until
refrigerated
and
frozen
at
200C
8
Plasma insulin pattern in Hausa-Fulani of northern Nigeria. Bakari A. G.
analysis. Following the withdrawal of fasting blood
samples, 75 grams of anhydrous glucose dissolved in
300ml of water was given to each subject. Each subject
completed this within five minutes; the time of
commencement of the drink is recorded as time zero
minute of oral glucose tolerance test (OGTT). Blood
samples were taken at tunes 30, 60, 90 and 120 minutes
of OGTT by temporarily stopping the slow saline
infusion for a minute. The blood samples were treated
just as the fasting samples. Insulin assay was performed
using a commercially available ELISA human insulin kit
(DRG instruments Gmbh, Marburg, Germany cat. no.
EIA 2935). The kit has inter-assay and intra-assay
coefficients of variation of 5.2 % and 4.8% respectively,
sensitivity of 99% for human insulin and does not cross
react with proinsulin.
Results are presented as mean + standard deviation.
Logarithmic transformation of plasma insulin values
was done before analysis, as the raw values were not
normally distributed.
between the two groups, p = 0.4187. The respective
values were 5.62 + 2.70 and 5.91 + 1.94 micromoles per
liter.
The mean plasma insulin levels and the range of
values observed following oral glucose administration
are shown on table 1 with the corresponding plasma
glucose levels.
Figure 1: Fasting plasma insulin levels in a Hausa Fulani
group in northern Nigeria
10
A total of 36 volunteers who met the inclusion criteria
participated in the study. This was made up of 12
(33.3%) females and 24 (66.7%) males. Mean age was
48.6 + 9.8 years (range 36-69 years). Nine (23%) of the
subjects had body mass index of greater than 25kgm-2
and were considered overweight.
There were marked individual variations in the
fasting plasma insulin levels necessitating logarithmic
transformation (Figure 1). Six (16.7%) individuals had
fasting plasma insulin levels more than 2 SD above the
mean and were regarded as exhibiting fasting
hyperinsulinaemia. Marked individual variation was also
noted in the plasma insulin response following oral
glucose challenge. The mean + standard deviation (SD)
fasting plasma insulin level among the 36 subjects was
5.72 + 2.16.
When the groups were subdivided as overweight and
normal weight, there was no significant difference
LOG. PLASMA INSULIN LEVEL.
Results
1
0.1
INDIVIDUAL PATIENTS.
Table 1: Mean plasma glucose and mean plasma insulin levels during OGTT in a Hausa-Fulani population in
northern Nigeria
OGTT time
Plasma glucose (mmol/L)
Fasting
3.95 + 0.49
30 minutes
7.55+ 0.42
60 minutes
6.94+ 0.54
90 minutes
6.45 + 0.47
120 minutes
5.63+ 0.51
Values are presented as mean + S.D
Discussion
Fasting plasma insulin levels in this study were similar
to the ones earlier reported by Ezenwaka et al 10 and
Osei et al 9 in southwestern Nigeria. They respectively
reported mean + standard deviation values of 5.8 + 5.6
Plasma insulin (micro-units/ml)
5.72 + 2.16
15.58 + 2.51
13.67 + 2.46
10.84 + 2.41
8.03 + 2.38
micro-units/ml and 4.5 + 1.8 micro units respectively for
fasting plasma insulin levels among the Yoruba ethnic
group of southwestern Nigeria. But much lower than
the value of 29.1 + 5.4 micro units /ml reported in
normal
Plasma insulin pattern in Hausa-Fulani of northern Nigeria. Bakari A. G.
African subjects in South Africa by Omar and Asmal.
Although it is difficult to distinguish the effect of race
from other confounding factors such as diet, there is
compelling evidence to suggest a role for racial factors
in modulating insulin secretion. Normoglycaemic Pima
Indians for example have been shown to produce two to
three times as much insulin when compared to their
Caucasian counterparts. 6 Similarly, plasma insulin
levels both basal and following oral glucose challenge
has been shown to be significantly and consistently
higher among Micronesians compared to their
Polynesian counterparts despite comparable levels of
glycaemia. 5 However, Kuku and Boyo 8 in a study of
forty healthy Africans in Lagos western Nigeria found
plasma insulin levels comparable to those reported for
Caucasians. This could be attributable to the
metropolitan nature of Lagos with life-styles comparable
to that obtained in Caucasian communities.
It is note worthy and indeed worrisome that 16.7%
of the subjects in this study demonstrated fasting
hyperinsulinaemia, this perhaps is due to the changes in
life styles that is been witnessed in most developing
countries. Anecdotal evidence suggests that more and
more people in this environment especially residents of
urban areas, are increasingly living more sedentary
lifestyles in addition to consumption of more refined
foods. In southwestern Nigeria, Ezenwaka et al 10 had
expectedly found tendency to hyperinsulinaemia to be
more common among urban dwellers than rural dwellers
near Ibadan.
Differences in dietary composition between the
populations may explain some of the differences
observed. It is known that high total and saturated fat
intake are associated with higher fasting plasma insulin
concentrations while high dietary fiber is associated
with low fasting insulin levels. 7 Other factors such as
glucose intolerance or hypertension have been excluded
by the selection criteria used in this study. Following
oral glucose administration, the plasma insulin response
was as expected brisk and proportional to the prevailing
plasma glucose levels.
Although the sample size is limited by availability of
resources, the finding of hyperinsulinaemia in more than
16% of subjects in this study is worrisome considering
the emerging role of insulin resistance as a
cardiovascular risk factor. Obviously larger prospective
studies on the beta-cell function and insulin sensitivity
in this population are required.
15
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
References
14.
1.
2.
Modan M, Halkin H, Almong S et al.
Hyperinsulinaemia a link between hypertension,
obesity and glucose intolerance. J Clin Invest1985;
75:809-817.
Defronzo R. A, Ferrarini E. Insulin resistance: a
multifaceted syndrome responsible for NIDDM,
obesity,
hypertension,
dyslipedaemia
and
15.
9
atherosclerotic cardiovascular disease. Diabetes
Care 1991; 14:173-191.
Ducimere P, Eschwege E Papoz L et al.
Relationship of plasma insulin levels to the
incidence of myocardial infarction and coronary
heart disease mortality in middle aged population.
Diabetologia 1980; 19:205-210.
Furlanetto R. W, Dicarlo J. N. Somatomedin Creceptors and growth effects in human breast cells
maintained in long-term tissue culture. Cancer Res
1984; 44:2122-2128.
Whitehouse K. S, Kiss J. Ethnic Variability in the
plasma insulin response to oral glucose in
Polynesian and Micronesian subjects. Diabetes
1979; 28: 624-628.
Aronoff S. L, Bennet P. H, Gorden P. Unexplained
hyperinsulinaemia in normal and prediabetic Pima
Indians compared with normal Caucasians. An
example of racial differences in insulin secretion.
Diabetes 1977; 26: 827-840.
Marshall J. A, Bessesen D. H, Hamman R. F. High
saturated fat and low starch and fiber are associated
with hyperinsulinaemia in a non diabetic
population. The San Luis Valley Diabetes Study.
Diabetologia 1997; 40; 430-434.
Kuku S. F, Boyo A. E. Plasma insulin and human
growth hormone patterns in an African population
Trop Geog Med 1979: 31:99-103.
Osei K, Cottrell D. A, Adejuwon C. A, Ezenwaka
E. C, Akanji A. O, O’Dorisio T. M. Serum Insulin
and glucose concentration in people at risk for type
II diabetes. A comparative study of AfricanAmerican and Nigerians. Diabetes care 1993; 16:
1367-1375.
Ezenwaka C. E, Akanji A. O, Osei K et al.
Glucose and insulin responses to intravenous
glucose challenge in relatives of Nigerian patients
with non-insulin-dependent diabetes mellitus. Diab
Res Clin Pract 1993; 20: 175-181.
World Health Organization: Definition, Diagnosis
and classification of diabetes mellitus and its
complications. Report of a WHO Consultation.
WHO, Geneva. 1999.
World Health Organization Expert committee:
Physical status; the use and interpretation of
anthropometry. Report of a WHO expert
committee. Technical report series 854. WHO,
Geneva. 1995.
Trinder P. Determination of Glucose in blood using
glucose-oxidase with an alternative oxygen
acceptor. Ann Clin Biochem 1969; 6:24-27.
Verstraete M. Clinical applications of inhibitors of
fibrinolysis. Drugs 1985; 29: 236-246.
Omar M.A. K, Asmal A. C. Insulin responses to
oral glucose in young African and Indian noninsulin dependent diabetic patients in Natal. Trop
Geog Med 1983; 35:59-64.