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Public Health Nutrition: 3(4), 425±431 425
Five-year follow-up of a food-based vitamin A intervention
in Tanzania
Diana Kidala
1
, Ted Greiner
2
and Mehari Gebre-Medhin
2,
*
1
Tanzania Food and Nutrition Centre, Dar-es-Salaam, Tanzania:
2
Department of Women's and Children's Health,
Section for International Maternal and Child Health, Uppsala University, S-751 85 Uppsala, Sweden
Submitted 4 October 1999: Accepted 7 January 2000
Abstract
Objective: To evaluate the long-term effects of a horticultural and nutrition education
intervention in rural Tanzania.
Design: A quasi-experimental post-test design was used.
Setting: The research was carried out in 10 villages in Singida region, Tanzania.
Subjects: Mothers and their children aged 6±71 months (n = 236) from an experi-
mental (Ilongero) and control (Ihanja) area were interviewed regarding knowledge
and practices related to vitamin A nutrition. Intake of vitamin A-rich foods by the
children during the 7 days prior to the interview was recorded. Stools were examined
for helminths and serum samples were analysed for retinol and C-reactive protein
(CRP) (n = 146) for the children aged 12±71 months.
Results: Knowledge and practices were more favourable to vitamin A intake in the
experimental area than in the control area, and an increased frequency of intake of
green leaves was associated with higher serum retinol values. The experimental area
had lower mean serum retinol levels (13.7 mgdl
-1
, n = 75) than the control area
(19.3 mgdl
-1
, n = 71). One likely confounder was the higher helminth infestation in
the experimental area (n = 75, 79%) than in the control area (n = 71, 49%) (P , 0.001).
Children with helminths (n = 94) had a lower mean serum retinol level than those
without (n = 52) (12.3 6 5 vs. 24 6 10 mgdl
-1
; P = 0.001).
Conclusions: Food-based vitamin A programmes can make sustainable improvements
in knowledge and dietary practices but these may not necessarily be re¯ected in
increases in serum retinol. Programme implementation and evaluation should take
confounders into consideration as, in this case, helminth infestation.
Keywords
Nutrition education
Vitamin A
Helminths
Children
Nutrition intervention
Food
Serum retinol
Tanzania
It is estimated that vitamin A de®ciency (VAD) and
xerophthalmia occur in about 6% of the Tanzanian
population, 98% of those affected being children under 6
years of age
1
. This de®ciency is a problem of public health
signi®cance mainly in the dry regions of central Tanzania
2
.
As an immediate measure for controlling VAD, vitamin A
supplements are to be provided to children with
xerophthalmia, acute respiratory infections, protein
energy malnutrition, prolonged diarrhoea and measles.
To achieve a more sustained impact, emphasis is being
placed on increased production and consumption of
vitamin A-rich foods, control of childhood diseases
through immunization and good environmental sanita-
tion, and promotion of breast-feeding and appropriate
weaning foods. Nutrition education is one of the strategies
used for these purposes
3
.
It is now widely accepted that vitamin A is important in
reducing mortality in children
4,5
, especially from deaths
which are attributed to diarrhoea and measles
5
. Improve-
ment of the vitamin A status of young children in areas
where clinical signs of de®ciency are evident has been
reported to reduce their mortality rate by 23%
6
. Night
blindness and xerophthalmia have been associated with
infrequent consumption of foods containing vitamin A
7±9
.
Some studies have found that intestinal helminths
appear to have a negative impact on vitamin A status
10,11
while others have not
12,13
. Higher levels of formal educa-
tion among mothers are associated with higher nutritional
status
14,15
. Speci®c nutrition education to improve con-
sumption of foods containing vitamin A has been reported
to be effective
16±18
. However, few studies have looked into
the extent to which the results of nutrition education
are sustainable and can still be observed beyond the
intervention period
19,20
.
Increasing the supply of affordable food sources can
also be effective. Home gardens, for example, can con-
tribute to vitamin A intake and status
21,22
. Improvements
in food processing and preparation techniques can also
be effective. For example, solar-dried provitamin A fruits
and vegetables for use during periods of scarcity tend
to have a higher provitamin A content than sun-dried
ones
23
.
q 2000 Nutrition Society* Corresponding author: Email Mehari,Gebre-Medhin@kbh.uu.se
426 D Kidala et al.
Concern has been raised about the effectiveness of
nutrition education in improving the diets of poor women
if given in isolation of programmes that make improve-
ments affordable
24
. Yet, in one study increases in house-
hold income were not signi®cantly associated with the
intake of dietary vitamin A to preschool children
25
. There
is also little documentation of the impact of nutrition
education interventions on knowledge, practices or
nutritional status in an African setting
26
, particularly with
respect to vitamin A intervention
27
. Further studies are
needed to elucidate the whole chain of events from
nutrition education through improved knowledge and
practice to an enhanced vitamin A status, particularly their
sustainability in natural settings. In addition, the role of
possible confounders such as infections in these interven-
tions needs to be further investigated.
A horticulture and nutrition education intervention had
been carried out in the arid VAD-prone area of Singida,
Tanzania in 1992/93. The present study was conducted
5 years later to look at programme sustainability and
examine the possible impact of that programme on the
knowledge and practices of the mothers in the area and on
the vitamin A status of their preschool children. We also
looked at the occurrence of intestinal helminths in the
children, a possible confounder of nutritional status.
Materials
The surveys
A survey was carried out in November 1991 among
preschool children aged 6±71 months in 10 villages in the
semiarid Ilongero and Ihanja Divisions in the Singida Rural
District of Tanzania. Five villages in each division were
randomly selected and data on serum retinol were
collected among 226 children, 6±71 months of age. The
results indicated that vitamin A de®ciency was a serious
public health problem: about 15% of the total sample
had severe de®ciency (serum retinol , 10 mgdl
-1
) and
another 47% had low levels (serum retinol , 20 mgdl
-1
)
28
.
Immediate measures were taken on behalf of all who took
part in the study and showed signs of VAD or other
diseases.
A pilot project based on long-term measures relevant for
rural Tanzanian communities was then initiated in the ®ve
villages in the Ilongero Division with the aim of promoting
increased production and consumption of vitamin A-rich
foods and enhancing proper preparation of these foods
(Table 1).
It was decided in 1998 to conduct a second survey in the
same villages as in 1991, to evaluate whether sustainability
had been achieved and to obtain information for potential
replication to other affected areas. In this study Ilongero
Division will be referred to as the experimental area and
Ihanja Division as the control area.
The survey was conducted in November±December
1998 before the rains started, and thus controlled for
possible seasonal effects. Apart from a summary report
28
,
data from the baseline survey were not available and thus a
quasi-experimental post-test design was used in the present
study for comparing the control and experimental areas.
Study population
All households of the 10 villages, ®ve in the Ilongero
Division and ®ve in the Ihanja Division, with children aged
Table 1 Activities performed in the Ilongero Division, 1992±1993
Activity People involved Outcome Year
Sensitization meeting for village Virtually all villagers 1992
leaders and villagers conducted
by TFNC
Two-day seminar on project Village leaders and 1992
implementation and nutrition PIC in each village
education to PIC and village leaders
by TFNC
Sensitization meeting by the PIC on: Virtually all villagers
X 7000 guava and pawpaw seedlings 1992
X Problems associated with not eating distributed to HH and primary schools
vitamin A-rich foods
X Proper preparation and storage of X 1800 HH (76% of HH) established
vitamin A-rich vegetables gardens
X Growing of vegetables and fruits X All primary schools established/
rich in vitamin A strengthened school gardens
Two-day nutrition education seminar 20±30 women in each
X 119 women trained 1993
conducted by TFNC on: village selected from
X Booklets distributed on:
X Importance of backyard gardens area of the village Vitamin A de®ciency and associated
X Traditional vegetable preservation problems (100 copies)
X Weaning foods Weaning foods for Singida region
X Vegetable cooking (100 copies)
Breast-feeding posters (20 copies)
HH, households; PIC, Project Implementation Committee; TFNC, Tanzania Food and Nutrition Centre.
427Food-based vitamin A intervention
6±71 months, were listed, using the village register. Each
village has approximately 200±300 households and the
number of those with children aged 6±71 months ranged
from 50 to 180. A table of random numbers was used to
select 25 households in each village, giving a total of 250
households. The procedure for the selection of house-
holds and subjects is illustrated in Fig. 1. If the mother was
not in the household on the day of the interview, then the
nearest eligible household was chosen. If there was more
than one preschool child in the household, an index child
was randomly selected. Fourteen were not at home and no
nearby replacements could be located. This resulted in 236
mother±child pairs (with an age range of 6±71 months)
who were interviewed, as shown in Fig. 1. The ®nal study
population on which our retinol analyses are based was
146. In Table 2, these children are compared with those
who are not included in the analysis for practical reasons.
Most of those who were not included in the analysis
were very young children; the ®nal sample includes no
children under 12 months and only seven children were
12±23 months old.
Methods
A structured questionnaire was used, including questions
on the health status of the child, review of the child's MCH
Fig. 1 The research subjects from the experimental and control areas
428 D Kidala et al.
card, mother's knowledge and practices related to vitamin
A nutrition, and the frequency of consumption during the
past week of vitamin A-rich foods. Observations were also
made of the presence of a home garden and the types of
vitamin A-rich crops grown. The mother was asked about
the number of days during the past week on which each of
a list of vitamin A-rich foods was eaten by the index child.
The informed consent of the mother was obtained
before participation in the research. Ethical clearance was
obtained from the Ethics Committee, Faculty of Medicine,
Uppsala University and from the Tanzania Food and
Nutrition Research and Ethics Committee.
Measurements of health indicators
Anthropometric measurements were made on 225 of the
236 children. Weight was measured without shoes and
with minimal clothing, using a battery-powered digital
scale (Seca Inc., Columbia, MD) and recorded to the
nearest 0.1 kg. Height was measured with a measuring
board marked in 0.1 cm divisions.
Stools (n = 225) were examined in the ®eld using a wet
preparation technique on a light microscope under low
power on the same day to determine whether or not
helminth eggs were present. About 5 ml of venous blood
was taken from the cubital vein, using disposable syringes
and needles, for determination of serum retinol and CRP.
CRP is an acute-phase reactant that was used to indicate
possible infection or an in¯ammatory process among
the children
29
. The blood samples were covered with a
black cloth and left for 15 min at room temperature, and
then transferred to a cool box. Within a few hours, the
samples were centrifuged and serum was separated and
frozen at - 308C pending analysis. The samples were
transported within 1 month to the laboratory in a frozen
condition.
Analytical procedures
The frozen samples were analysed for serum retinol within
1 month of arriving at the laboratory, using high per-
formance liquid chromatography (HPLC)
30
. The between-
series coef®cient of variation was 15%. CRP was assayed
by an enzyme-linked immunoadsorbent assay (ELISA)
technique using in-house kits from DAKO (A/S Denmark)
and a computerized Multiskan Eliza reader (Labsystems
Finland). The detection level for CRP was 0.02 mg l
-1
.
The normal reference interval used for the study area was
CRP , 10 mg l
-1
.
Statistical analysis
The Statistical Package for the Social Sciences (SPSS version
9.0) was used for data analysis. Differences between the
experimental and control groups were calculated con-
cerning variables related to knowledge, practice, serum
retinol levels, and the number of days per week on which
individual vitamin A-rich foods were eaten. Appropriate
parametric or non-parametric statistical tests were chosen
according to whether or not variables were normally
distributed. The Mann±Whitney test, Pearson chi-square
and Spearman's correlations were used.
Results
Knowledge and practices
Knowledge and practice, as measured by the indicators
shown in Table 3, differed markedly between the two
areas. Knowledge about possession of and use of solar
driers was signi®cantly higher in the experimental area.
Sixty-seven per cent of the experimental households
were observed to have a home garden and 67% of these
households were growing pawpaws and/or guavas
(provided by the Tanzania Food and Nutrition Centre
(TFNC)), compared to 32% and 20% in the control area,
respectively (P = 0.001 in each case). Sixty-®ve per cent of
the index children in the experimental area consumed
vitamin A-rich foods more than 7 times a week, compared
to 37% in the control area (P = 0.001). Addition of fat to the
child's diet was similar in both areas but colostrum use was
slightly higher in the experimental area.
C-reactive protein
The serum concentration of CRP ranged from 0.5 to
29.1 mg l
-1
in the total study population (n = 161). All the
Table 2 Some characteristics of the children in the ®nal study population compared with those not included in the
retinol analysis (RA)
Experimental area Control area
Final study Not included Final study Not included
population in RA population in RA
Number 75 46 71 44
Mean age (years) 47 6 14 35 6 16 49 6 12 43 6 16
Girls/Boys (%) 51/50% 52/48% 48/52% 57/43%
Mean consumption of DGLVs 4.5 6 3.0 5.3 6 2.9 3.2 6 2.8 3.0 6 3.2
% with helminths 79% 70% 49% 59%
DGLV, dark green leafy vegetable.
429Food-based vitamin A intervention
children in the experimental group (n = 75) and 71 of
those in the control group had CRP < 10 mg l
-1
, i.e. within
the normal reference interval. Four children did not have
suf®cient blood for retinol analysis and 11 children had
CRP values . 10 mg l
-1
. Children with CRP . 10 mg l
-1
were excluded from further data analysis as were six
children for whom CRP values were not known.
Serum retinol
The serum retinol levels ranged from 2.2 to 55.1 mgdl
-1
(n = 146) in the ®nal study population; 22% had severe
VAD (serum retinol , 10 mgdl
-1
) and 53% had low levels
(retinol , 20 mgdl
-1
). The more often the children
consumed green leafy vegetables, the higher their serum
retinol (Spearman's rho = 0.21, P = 0.01). Five children
among the 146 were still breast-feeding, one of whom was
12 months old, and the remaining four were between the
ages of 22 and 38 months. There was no statistically
signi®cant difference between the mean serum retinol for
those who were still breast-feeding (15.2 6 12.5 mgdl
-1
)
and those who had stopped breast-feeding (16.2 6
9 mgdl
-1
, P , 0.65). Only one of these ®ve breast-fed
children had helminths, with a serum retinol level of
11.2 mgdl
-1
, while the corresponding mean for the four
without helminths was 16 6 14 mgdl
-1
. The children in the
control area (n = 71), where no intervention was carried
out, had a signi®cantly higher mean serum retinol (19.4 6
9 mgdl
-1
) than those in the experimental area (n = 75)
(14 6 8 mgdl
-1
)(P , 0.0001).
Impact of helminths on retinol
Of the children for whom retinol values are known
and whose CRP levels were < 10 mg l
-1
, 79% in the
experimental villages (n = 75) and 49% in the control
villages (n = 71) were infested with helminths (Pearson
chi-square = 13.7, P = 0.0002) (Table 4). The children with
helminths in the two divisions combined (n = 94) had
signi®cantly lower mean serum retinol level (12.3 6
5 mgdl
-1
) than those without helminths (n = 52) (24 6
10 mgdl
-1
)(P = 0.001) (Table 5). The difference in serum
retinol between the experimental and control areas was no
longer statistically signi®cant when adjustment was made
for helminth infection.
Receipt of vitamin A capsules
There was no signi®cant difference between the two areas
regarding the reported receipt of vitamin A capsules. Seven
children in the experimental area and six in the control
area had received such capsules. However, the capsules
were received more than 6 months before the survey was
carried out. The mean serum retinol level in the children
receiving capsules in the experimental area was 10.0 6
9 mgdl
-1
(n = 7) and in the control area it was 20.9 6
4 mgdl
-1
(n = 6). A possible explanation for this difference
is that a greater proportion in the experimental group had
Table 3 Knowledge and practices in the control and experimental areas
Experimental area Control area
(n = 121) (n = 115)
Knowledge/practice (%) (%) P value
Agreed that solar drier is important 90 28 0.001
Household has a solar drier 44 0 0.001
Household uses solar drier/shade 43 1.8 0.001
Household has home garden 67 31 0.001
Grows carotene-rich crops provided by TFNC 67 28 0.001
Child consumed vitamin A-rich foods . 7 times in last week* 65 37 0.001
Adds fat/oil to child's food 93 93 0.5
Gives her infants colostrum 95 84 0.018
* In analysing data based on a 1-week frequency recall, WHO recommends that three times per week be used as a cut-off point
36
. But when
used with our data, this cut-off point was too low to discriminate between the two areas. Thus we chose a cut-off of greater than seven times
in the past week (close to the mean).
Table 4 Type of helminth infestation and number infected (per cent in brackets)
Hookworm and
Not infected Ascaris lumbricoides Hookworm A. lumbricoides
Control 36 (51) 34 (48) 0 1 (1)
(n = 71)
Experimental 16 (21) 53 (71) 6 (8) 0
(n = 75)
Table 5 Mean serum retinol (mgdl
-1
) in relation to helminth
infection
Villages Not infected Infected
Experimental and control 24.0 (n = 52)* 12.3 (n = 94)**
combined
Control 25.2 (n = 36)* 13.3 (n = 35)**
Experimental 21.2 (n = 16) * 11.7 (n = 59)**
Only when the asterisks are different are differences statistically signi®cant
(P , 0.05).
430 D Kidala et al.
helminths. The mean serum retinol level in children with
helminths in the experimental group was 5.6 6 3 mgdl
-1
(n = 4). The single child with helminths who had received
vitamin A capsules quite a few years earlier in the control
area had a serum retinol of 13.4 mgdl
-1
.
Discussion
The objective of the present study was to ®nd out whether
a horticulture and nutrition education programme pre-
viously carried out in a VAD-prone area of Tanzania
had been successful in sustaining positive changes in
knowledge and practices of the population towards an
improvement of the vitamin A status of their children. An
area in which no such intervention had been conducted
served as a control area.
Similar to ®ndings elsewhere
17,18,31
, the intervention
programme appeared to have a positive impact on some
indicators of nutrition knowledge and practice in the
experimental area compared with the control area.
Smitasiri et al.
31
and Hussain and Kva
Ê
le
19
found evidence
in Asia that such improvements can be sustainable. Here
we provide similar results in an African context.
However, the experimental area had a signi®cantly
lower mean serum retinol than the control area. Others
have reported no evidence of improvement in vitamin A
status despite increases in consumption
31
. Greiner and
Mitra
17
reported from a study in Bangladesh that night
blindness levels were not signi®cantly decreased either by
an increase in consumption of vitamin A-rich foods after a
nutrition education intervention in the experimental area
or by an increase in vitamin A capsule coverage in the
control area. In rural India, Vijayaraghavan et al.
18
found
that, although there were improvements in knowledge,
production and consumption of vitamin A-rich foods, the
impact on the prevalence of Bitot's spot was not statisti-
cally signi®cant and the mean serum retinol levels in the
children participating in the trial did not differ signi®cantly
from those of non-participants.
In contrast, after a 3-year intervention programme of
nutrition education and health promotion, Kuhnlein et al.
32
reported improvements in serum retinol, carotene and
folate levels in the overall community and in the iron status
of teenagers, compared with the baseline values. Similarly,
in Bangladesh, Hussain et al.
8
found that 3 years of nutrition
education was associated with reduced frequencies of night
blindness. However, both studies lacked control areas and
thus we cannot rule out secular change as an explanation
for their ®ndings.
In the present study, one likely reason for the unexpected
®ndings was the higher proportion of children with
helminth infestation in the experimental villages than in
the control villages. Children with helminths had sub-
stantially lower levels of retinol than those without. When
consideration was paid to helminth infestation in the
analyses, there was no statistically signi®cant difference in
serum retinol levels between the study areas. In Brazil,
Marinho et al.
33
found that supplementation with vitamin
A and/or zinc was effective in raising the blood vitamin A
levels only in parasite-free children. Similarly, in a study in
Nepal it was found that children who had been given
at least one course of mebendazole during the past
12 months had higher serum retinol levels than those who
had not received this anthelminthic
34
. On the other hand,
in areas with adequate access to vitamin A-rich foods and a
good vitamin A status, the effect of helminths may be
negligible, as shown in a study in Zanzibar
35
.
The post-test quasi-experimental evaluation method
used here is subject to the risk that the experimental and
control areas were not equivalent at baseline. While we
were unable to obtain the baseline data, data in the
existing report
28
suggest that the overall retinol status was
similar at baseline in the two areas. Although we do not
know if other variables were also similar at baseline, it is
highly plausible that many of the differences we found
were due to the effects of the intervention. The clearest
examples are related to awareness and use of solar driers,
as shown in Table 3. It is evident from the studies men-
tioned above, that in the chain of events leading from
nutrition education to improved knowledge and practice
and hence a better vitamin A status, confounders can
obscure the bene®cial effects of interventions.
We conclude that nutrition education programmes
initiated to improve dietary intake can lead to increases
in knowledge and that people can change their practices
for the better. These changes can be sustained over time
and yet not be re¯ected in serum retinol values. Thus,
consideration should be paid to factors that may stand in
the way of improvement in nutritional status ± in this case,
helminth infestation. Further studies are needed to look in
more detail at the interactions of various factors, both
biological and otherwise, that may hinder improvement in
the vitamin A status in natural settings and thus undermine
the effectiveness and sustainability of interventions.
Acknowledgements
The authors wish to acknowledge the Tanzania Food and
Nutrition Centre (TFNC) for conducting the laboratory
analyses and helping with the ®eldwork. We would also
like to thank the TFNC and the Swedish International
Development Cooperation Agency (Sida) for funding the
research, and the Swedish Institute for providing a guest
scholarship to Diana Kidala.
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