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African Journal of Food, Agriculture, Nutrition and Development
Rural Outreach Program
ISSN: 1684-5358 EISSN: 1684-5374
Vol. 9, Num. 6, 2009, pp. 1294-1308
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African Journal of Food Agriculture Nutrition and Development, Vol. 9, No. 6, Sept, 2009, pp. 1294-1308
Evaluation Of A Green Leafy Vegetable Intervention In Ghanaian
Postpartum Mothers
Tchum
SK1, Newton S1*, Tanumihardjo SA2, Fareed
KNA3, Tetteh A3 and S Owusu-Agyei1
*Corresponding
author email: sam.newton@ghana-khrc.org
1Kintampo Health Research Centre, Health Research Unit, Ministry of
Health, P.O. Box 200, Kintampo, Brong Ahafo Region, Ghana
2University of Wisconsin-Madison; Dept. of Nutritional Sciences, 1415 Linden Dr., Madison, WI 53706 USA.
3Department of Biochemistry, Kwame Nkrumah University of Science and Technology, Ghana.
Code Number: nd09063
ABSTRACT
Vitamin A
deficiency is a major public health problem in many developing countries and
women of childbearing age and children are most affected. Low dietary intakes
and increased requirements during different life stages contribute to
inadequate vitamin A liver reserves and hence the importance of assessing
vitamin A status to determine population groups at risk of deficiency. This
study was a community-based, exploratory intervention trial of postpartum
mothers selected from villages in Ejisu/Juabeng District of the Ashanti Region
in Ghana. The objective was to determine the improvement in vitamin A status of
postpartum Ghanaian mothers fed daily with African eggplant leaves using the
modified-relative-dose-response (MRDR) test for indirect assessment of liver
vitamin A stores. Potential mothers were visited at home by trained field
workers 7-10 days after their delivery and recruited into the trial. Baseline
MRDR tests were performed for all the women (n = 61). The women were randomly
assigned into control (n =10) and intervention (n =51) groups and invited back
each month for follow-up MRDR assessment over period of three months. A daily
portion of 200 g (2.6 mg of Beta-carotene) of African eggplant leaves were
given to mothers in the intervention groups for three months while those in the
control group did not receive any additional vegetables. The baseline mean
serum retinol concentration and MRDR value were 1.5 ± 0.6 μmol/l and 0.09
± 0.05 respectively indicating a marginal vitamin A status. Serum retinol
concentrations did not differ between (p = 0.47) and within the two groups by
time point (p= 0.41). The African eggplant leaves were well accepted and there
was a significant improvement in the vitamin A status as assessed by MRDR test
within the intervention group over the three months period (P = 0.0001).
Vitamin A status also improved in the control group but there was loss of
statistical power due to number of dropouts. Dietary modification and nutrition
education to women of childbearing age to include natural food sources rich in
provitamin A may provide the long-term solution to prevent vitamin A deficiency
in developing countries because indigenous leafy vegetables can be easily
cultivated in our communities making them sustainable and cheaper compared to
periodic oral dosing with vitamin A.
Key words: Vitamin A, 3, 4-Didehydroretinol, -Carotene, Vitamin A
status
INTRODUCTION
The vitamin A
status of under-privileged women and children is compromised and this is
exacerbated by low socio-economic status [1-4]. Low dietary intakes and
increased requirements during different life stages contribute to inadequate
vitamin A liver reserves. Assessing vitamin A status is important in
determining which population groups are at risk of deficiency [5]. Serum
retinol concentrations are homeostatically controlled and do not begin to
decline until liver reserves are dangerously low [6]. In times of infection,
serum retinol concentrations are reduced due to the acute phase response [7].
Moreover, during acute infection, retinol is excreted in significant amounts in
the urine, increasing requirements [8].
Liver reserves
less than 0.070 mol retinol/g are considered deficient [9]. The
modified relative dose response (MRDR) test is an indirect measure of liver
vitamin A reserves. As liver vitamin A reserves become depleted, apo-retinol
binding protein (RBP) accumulates in the liver. When an oral dose of vitamin A
is administered, the freshly absorbed retinol is rapidly liganded with the
accumulated apo-RBP and is released into plasma; if 3,
4-didehydroretinol ester is given orally, 3, 4-didehydroretinol is also
released as its complex with RBP. For the MRDR test, a precise dose of 3,
4-didehydroretinyl acetate is administered and the ratio of 3, 4-didehydroretinol
to retinol (MRDR value) in serum at 4 to 6 hours after dosing is determined.
Less adequate liver vitamin A stores will result in a greater ratio of 3,
4-didehydroretinol to retinol in serum [5]. The MRDR test distinguishes
between moderately inadequate and adequate vitamin A status; MRDR values ≤
0.030 have been defined as indicating vitamin A adequacy in humans, 0.030 to
0.060 is uncertain vitamin A status, and MRDR values more than 0.060 indicate
vitamin A deficiency [10].
This study
followed a high-dose vitamin A supplementation trial among lactating women in Ghana. Lactating women in Ghana have a marginal vitamin A status, as assessed by the MRDR
test, and high-dose supplements were able to protect the women from vitamin A
depletion for at least 5 months postpartum [11]. In this study because the
vitamin A status of the mothers were defined as marginal, indigenous green
leafy vegetables rich in provitamin A may improve their vitamin A status
without the high-cost program implications of administering vitamin A capsules.
Multiple factors
affect the bioavailability of provitamin A carotenoids from vegetables
[12-14]. The MRDR test has successfully been used to monitor change in vitamin
A status after sweet potato feeding in South African children [15]. The leaf
chosen for this study was from the African eggplant (Solanum macrocarpon),
which is locally called Gboma and belongs to the Solanaceae family.
This is a regionally consumed, indigenous leafy vegetable (ILV) [16]. Limited
research indicates that these vegetables have good nutritive value as they
contain high levels of calcium, iron, phosphorus, vitamins and protein
[17-21].
Women of reproductive-age living with vitamin A
deficiency (VAD) frequently report night blindness during pregnancy and/or
lactation [22]. Night blindness in women during periods of increased
physiologic need is thought to reflect VAD. In a randomised community trial in
pregnant Nepalese women, ocular defects were reduced in their newborns by
weekly low-dose vitamin A supplementation [23]. During VAD there is a
reduction in the amount of vitamin A needed to support maternal reproductive
processes, including foetal growth and development, and to replace vitamin A
losses in breast milk during lactation. Many of the
epithelial tissues are important barriers to infection and VAD impairs this
function [24]. In VAD, keratin-producing cells replace mucus-secreting cells
in many epithelial tissues of the body which is the basis of the pathological
process known as xerosis in which there is drying of the conjunctiva and cornea
of the eye [25].
Studies in
pregnant women from Nepal, Philippines, Zambia, Ghana, and Mali have reported prevalence values for subclinical VAD (serum retinol <0.7 mol/L)
between 19-38% [11, 26-27]. The objective of this study was to assess the
vitamin A status of lactating women given green leafy vegetables by applying
the MRDR test over time.
SUBJECTS AND
METHODS
Subjects
The study was a
community-based, exploratory intervention trial of 77 postpartum mothers
selected from villages in Ejisu/Juabeng District of the Ashanti Region in Ghana. The Institutional Ethics Committee (IEC) of the Kintampo Health Research Centre,
Ghana Health Service approved the study protocol. Subjects were free to decline
to participate in the study and confidentiality of the information collected
was assured. To be eligible for recruitment into the trial, mothers were
expected to be resident in the villages in Ejisu/Juabeng District and express a
willingness to participate in the study by signing a consent form. Eligible
mothers had to generally be ingood health as determined by a medical
history and physical examination.
After baseline MRDR tests were done, 16
mothers refused blood draw and the rest were randomly assigned to two groups.
61 identical small white plastic discs comprising 51 intervention group discs
and 10 labeled control group discs were placed in an opaque plastic bag. 61
post partum mothers were assembled at baseline and asked to draw one labeled
disc from the bag and depending on which disc was drawn they were allocated to
the group indicated on the disc.
Each mother in
the intervention group (n = 51) received 200 g (2.6 mg -carotene) of
fresh African eggplant leaves daily for three months [28]. Fresh leaves ofAfrican
eggplant (Solanum macrocarpon) were collected from the Amanfro Prison
Camp farms in Kumasi and transported every three days to the study site for
distribution.
Mothers in the
control group (n = 10) did not receive African eggplant leaves. All women
received nutrition education messages concerning the inclusion of vegetables in
the diet. Subjects were visited weekly by trained fieldworkers (FWs) and
supplied with packets of indigenous leafy vegetables. The FWs checked for
compliance, answered questions, and educated the subjects on the importance of
vitamin A to the health of mothers and indirectly to their breastfed infant.
During monthly blood draws, subjects were further educated on the importance of
vitamin A and the coordinator answered questions which the FWs were not able to
address. There was a misconception that indigenous leafy vegetables were foods
meant for the poor and it was important that these misconceptions were
addressed. During the follow-up months, the MRDR test was performed in all
women who consented.
Modified
relative dose response test
The MRDR test
involves giving an oral dose of 8.8 μmol 3, 4-didehydroretinyl acetate
dissolved in corn oil in the morning. This amount corresponds to approximately
2500 µg Retinol Equivalents (7500 IU) vitamin A, which is an amount commonly
found in prenatal vitamins. However, the biological activity of 3,
4-didehydroretinol may be less than that of retinol [29]. The mothers were
dosed at their homes and five hours later a single finger prick blood sample
(500 μl) was taken. The blood samples were stored on ice in a
light-protected cooler until transported to the laboratory. Clotted blood
samples were centrifuged at 600 X g for 10 min, and serum was stored at 20oC
until shipped frozen to the University of Wisconsin-Madison (USA) at which time
they were stored at -80oC until analyzed.
Extraction
and high-pressure liquid chromatography (HPLC) assay
Serum was
thawed; 200 μl aliquots were treated with 250 μl ethanol and then
extracted thrice with 300 μl hexane. All extractions were done under gold
fluorescent lights. Retinyl acetate dissolved in ethanol was used as an
internal standard to determine extraction efficiencies. The hexane layers were
pooled and the solvent evaporated under argon. The residue was re-dissolved in
40 μl methanol:ethylene dichloride (3:1, v:v), of which 35 μl was
injected onto a 5 μm-Waters Sunfire 15 cm reversed-phase column
(Milford, Massachusetts, USA). The wavelength of detection was set at 350 nm
to optimize 3, 4-didehydroretinol detection and quantification. The mobile
phase was 74:20:6 methanol: acetonitrile:water (0.05% triethylamine) at a flow
of 1 ml/min. External standards of 3, 4-didehydroretinol and retinol were
purified by HPLC and used to quantify the 3, 4-didehydroretinol and retinol in
the serum samples. The leaf sample analysis was carried out using HPLC at the
Noguchi Memorial Institute for Medical Research, Ghana.
Statistical analysis
SAS statistical
computer software (version 8.2; SAS Institute, Cary, NC, 2001) was used in the
analysis of data. A repeated measures analysis of variance table was generated
using SAS PROC MIXED, which allows the treatment variances to be different
between the groups. The variance ratio (F) was calculated for serum MRDR values
and retinol concentrations in relation to subjects treatment groups and time.
The serum MRDR test and retinol concentration were treated as continuous
variables. The differences within the treatment groups by time were assessed
using the differences of Least Square Means (LSM). Values are presented as
means + standard deviations; p < 0.05 was considered significant.
RESULTS
Socioeconomic
factors
The number of
women who consented for participation in the study was originally 77. The
number of women that agreed to baseline and at least one MRDR follow-up
assessment was 61. Thirty-six percent of subjects were between 20 to 29 y, 18%
were between 30 to 45 y, and 33% did not know their age. The mean baseline
retinol concentration and MRDR values were 1.5 ± 0.6 µmol/l and 0.09 ± 0.05,
respectively. Sixty-nine percent of the subjects were married; 75% had
attended middle or junior secondary school; and 1% had attended post-middle
school, which was the highest level of education.
Vitamin A
status
At baseline
measurements, 47% and 70% of the women enrolled had insufficient vitamin A
liver reserves in the intervention and control groups, respectively (Table 1).
Vitamin A insufficiency is defined as a MRDR value > 0.060 and a
public health problem exists when > 20% of a community has values >
0.060 [10]. These percentages continued to decrease during the study. The
MRDR values indicated an improvement in vitamin A liver reserves from baseline
to each of the three follow-up times for both groups (Table 2). The overall
effect of time of treatment was significant (p < 0.0001). Vitamin A status
improved within the intervention group during the study. In the intervention
group, follow-up months one and two did not differ from baseline (p = 0.25),
but all other comparisons differed (p < 0.05) using differences of LSM. The
control group also had a significant improvement in the MRDR values and did not
differ from the intervention group during the study (Table 2), but a large
number of dropouts coupled with the smaller initial number enrolled in the
control group decreased the confidence in the data to conclude that nutrition
education alone can make an impact. Serum retinol concentrations did not
differ by group (p = 0.47) or time (p = 0.66).
Table 1: Percentage of
Ghanaian lactating women with insufficient vitamin A liver reserves in the
intervention and control groups. Insufficient vitamin A liver reserves were
defined as a modified relative dose response (MRDR) value of > 0.060.
Time points |
Intervention |
Control |
Subjects
(n) |
Subjects with
MRDR>0.060 |
% |
Subjects
(n) |
Subjects with
MRDR>0.060 |
% |
Baseline |
51 |
24 |
47 |
10 |
7 |
70 |
Month 1 |
43 |
14 |
33 |
8 |
4 |
50 |
Month 2 |
41 |
11 |
27 |
5 |
1 |
20 |
Month 3 |
34 |
1 |
3 |
5 |
0 |
0 |
Table 2: Effect of feeding with indigenous
leafy vegetables on modified relative dose response (MRDR) values over time for
lactating Ghanaian women in both intervention and control groups1
Time |
Green Leaf group MRDR value |
Control group MRDR value |
Baseline |
0.083 + 0.045a |
0.11 + 0.060a |
Month 1 |
0.058 + 0.027b |
0.068 + 0.020b |
Month 2 |
0.049 + 0.029b |
0.073 + 0.080b |
Month 3 |
0.025 + 0.016c |
0.014 + 0.010c |
1Superscript letters represent differences within each treatment
group using differences of least squares means. n = 51, 43, 41 and 34 for the
intervention group and n = 10, 8, 5, and 5 for the control group.
DISCUSSION
The Ghanaian
postpartum mothers had marginal liver reserves of vitamin A at baseline as
assessed by the MRDR test, which is indirectly related to liver reserves. The
mean serum retinol concentrations were high in these women (1.5 + 0.6 mol/l)
and much higher than what are considered deficient (i.e., < 0.7 mol/l)
or marginal in women (i.e., between 0.7 and 1.05 mol/l). A
previous study of rural Ghanaian women had similar serum retinol concentrations
(1.4 + 0.5 mol/l), but their mean MRDR value was half that found
in this study (0.048 ± 0.037) [11]. These findings contradict a simulated
analysis in which the difference found in MRDR values was said to occur because
of underlying different serum retinol concentrations [30]. Furthermore, the
serum retinol concentrations did not change either within or between groups
making it an insensitive indicator of changes in vitamin A status in these
Ghanaian women.
The intervention
group showed a steady decrease in their MRDR values over the three-month
period, indicating an improvement in vitamin A liver reserves. This finding is
very similar to a -carotene supplementation trial in lactating
Bangladeshi women where MRDR values decreased with time of supplementation
[31]. Another green leafy vegetable feeding study in Indonesian lactating
women did not show improvement in liver reserves [32]. Two major differences
between the Indonesian study and this study in Ghanaian postpartum women were
that the Indonesian women had poorer vitamin A status at baseline (0.81 +
0.04 to 0.89 + 0.04 mol/l) and they were fed less vegetable per
day, for example 100-150 g versus 200 g in this study. Therefore, an overall
change to adequate vitamin A status may not be expected, especially when the
intervention group is considered vitamin A deficient and lactating [26, 33,
34].
The vitamin A
status of the Ghanaian women in the control group also showed an improvement
during the trial, but the number of women remaining in the final assessment (n
= 5) was not statistically powered to conclude that nutrition education alone
could make a difference at the community level. Because the nature of the
intervention was not blinded, the women could have modified their diets during
this project. During this trial the community became aware of the importance
of vitamin A on maternal health and this may have influenced women to start
eating other indigenous leafy vegetables which were also rich in provitamin A
apart from the African eggplant leaves. Although attrition occurred in both
groups, the vegetable group maintained enough women to evaluate the vitamin A
status using the MRDR test in a longitudinal study. Attrition was due in part
to the repeated blood drawing nature of the study in this culture.
The serum
retinol concentrations of lactating women in Ghana indicate that they do not
have clinical VAD. However, their MRDR values indicate that they have a
depleted vitamin A status and will benefit from either supplementation or
dietary strategies [11]. Typically, vitamin A supplementation programs are
expensive to implement and sometimes coverage rates are not ideal. The
intervention study with African eggplant leaves shows promise as a means to
improve vitamin A status of postpartum mothers and the community in general.
Using the data obtained from the results presented herein, a more carefully
controlled study should be designed in separate villages of similar
socioeconomic status to see if this rich plant source could improve vitamin A
status at the community level in an intervention group versus a community with
no intervention.
Although the
study was not designed to look at effects of African eggplant leaves on breast
milk flow, an interesting observation was made that more than 80% of the
postpartum mothers in the intervention group reported an increase in the
secretion and flow of breast milk (galactogenic effect) throughout the feeding
period while none of the mothers in the control group reported such an
observation. This point warrants further evaluation in a controlled trial.
Periodic oral
dosing and food fortification have had documented success and have established
their merit in preventing nutritional blindness, but they are considered
expensive, temporary solutions. Long-term intervention through dietary
modification of the intake of foods rich in provitamin A and vitamin A may be
more effective [35, 36, 37]. The conversion factor for -carotene to
retinol for green leafy vegetables has been suggested to be 26 g -carotene
to 1 g retinol using changes in serum retinol concentrations [38].
However, data using more sensitive stable isotope methods to calculate changes
in total body reserves of vitamin A after feeding pureed spinach estimated a
conversion factor of 10:1 [39]. Data in a vitamin A-depleted animal model
which has predicted that vitamin A status is a major determinant of the
conversion factor calculated 3:1 for spinach, brussels sprouts, and kale [40].
Because the women in this study were vitamin A-depleted as assessed by the MRDR
test, conversion to retinol was probably favoured after absorption resulting in
a high conversion rate.
Biofortification
of staple crops with provitamin A carotenoids, e.g., maize and cassava,
or switching to more yellow- or orange-coloured local varieties will also
enhance vitamin A status [40, 41]. Among the benefits of promoting such
natural food sources is that they provide concurrent intake of other nutritive
and non-nutritive substances that contribute to the prevention of disease. For
example, fruits and vegetables consistently are shown to provide protection
against certain types of cancer [42]. Another benefit is the avoidance of the
potential toxicity associated with the over consumption of vitamin A
supplements [40, 43]. Thorough cost-benefit analyses of the three strategies
(vitamin A supplementation, food fortification, and dietary interventions) to
prevent and control VAD have yet to be made in Ghana. Because of the positive
outcomes of this community-based intervention, further work is warranted with a
larger sample size to better reflect community impact.
CONCLUSION
Nutrition
education and encouraging women to include locally grown green leafy vegetables
in their diets could be an important strategy to improve vitamin A status. There
is the need to identify their nutritional value due to their potential to
overcome micronutrient deficiencies. Dietary modification to include natural
food sources rich in provitamin A may provide the long-term solution to
prevent VAD in developing countries because indigenous leafy vegetables can be
easily cultivated in our communities making them sustainable and cheaper
compared to periodic oral dosing with vitamin A.
ACKNOWLEDGMENT
This research
was supported by an International Atomic Energy Agency fellowship to SK Tchum.
The authors gratefully thank Rebecca Surles for her unselfish time spent in
training on the appropriate analysis of the MRDR test in the Tanumihardjo
laboratory and Peter Crump, UW-Madison College of Agriculture and Life Sciences
Statistical Consulting Service, for providing statistical consultation. The
authors also thank Harold Furr for editorial assistance. Many thanks to all
staff of Kintampo Health Research Centre who assisted in field activities;
special thanks to George Adjei, who assisted with data management.
REFERENCES
- Tanumihardjo SA, Permaesih D, Dahro AM,
Rustan E, Muhilal, Karyadi D and JA Olson
Comparison of vitamin A status assessment techniques in children from two
Indonesian villages. Am. J. Clin. Nutr. 1994; 60: 136-141.
- Tanumihardjo SA, Muherdiyantiningsih,
Permaesih D, Dahro AM, Muhilal, Karyadi D and JA Olson Assessment of the vitamin A status in lactating and nonlactating,
nonpregnant Indonesian women by use of the modified-relative-dose- response
(MRDR) test. Am. J. Clin. Nutr.1994; 60: 142-147.
- Tanumihardjo SA, Suharno D, Permaesih D, Muherdiyantiningsih,
Dahro AM, Muhilal, Karyadi D and JA Olson
Application of the modified relative dose response test to pregnant Indonesian
women for assessing vitamin A status. Eur. J. Clin. Nutr. 1995; 49: 897-903.
- Duitsman PK,
Cook LR, Tanumihardjo S and JA Olson Vitamin A
inadequacy in socioeconomically disadvantaged pregnant Iowan women as assessed
by the modified relative dose response (MRDR) test. Nutr. Res. 1995; 15: 1263-1267.
- Tanumihardjo SA Assessing vitamin A status: past, present and future. J. Nutr. 2004; 134: 290S-293S.
- Underwood BA Vitamin
A in animal and human nutrition. In: Sporn MB, Roberts AB, and DS
Goodman (Eds). The Retinoids vol. 1. Orlando, FL: Academic Press, 1984:
281-391.
- Clausen SW and AB McCoord The carotenoids and vitamin A of the blood. J.Pediatr.
1938; 13: 635-650.
- Stephensen CB, Alvarez JO, Kohatsu J,
Hardmeier R, Kennedy JI Jr and RB Gammon Jr. Vitamin A is excreted in the urine during acute infection. Am. J. Clin.
Nutr. 1994; 60: 388-392.
- Olson JA Vitamin
A. In: Rucker RB, Suttie JW, McCormick DB and LJ Machlin (Eds).
Handbook of Vitamins, 3rd edition. New York, NY: Marcel Dekker,
2001: 1-50.
- Tanumihardjo SA, Cheng JC, Permaesih D, Muherdiyantiningsih,
Rustan E, Muhilal, Karyadi D and JA Olson Refinement of the modified-relative-dose-response test as a method for
assessing vitamin A status in a field setting: experience with Indonesian
children. Am. J. Clin. Nutr. 1996; 64: 966-971.
- Tchum SK, Tanumihardjo SA, Newton S, de
Benoist B, Owusu-Agyei S, Arthur FK and A Tetteh
Evaluation of vitamin A supplementation regimens in Ghanaian postpartum mothers
with the use of the modified-relative-dose-response test. Am. J. Clin. Nutr. 2006: 84; 1344-9.
- De Pee S and CE West Dietary carotenoids and their role in combating vitamin A
deficiency: a review of the literature. Eur. J. Clin. Nutr. 1996; 50 Suppl 3: S38-353.
- Williams AW, Boileau TW and JW Erdman Jr Factors influencing the uptake and absorption of carotenoids. Proc.
Soc. Exp. Biol. Med.1998; 218: 106-8.
- Tanumihardjo SA Factors influencing the conversion of carotenoids to retinol: bioavailability
to bioconversion to bioefficacy. Int. J. Vitam. Nutr. Res. 2002; 72: 40-45.
- Van Jaarsveld PJ, Faber M, Tanumihardjo SA,
Nestel P, Lombard CJ and AJ Benade
Beta-carotene-rich orange-fleshed sweet potato improves the vitamin A status of
primary school children assessed with the modified-relative-dose-response test.
Am. J. Clin. Nutr. 2005; 81: 1080-1087.
- Smith FI and P Eyzaguirre African leafy vegetables: their role in the world health
organizations global fruit and vegetables initiative. African J. of Food
Agriculture Nutrition and Development Online 2007: 7(3). Available from
www.ajfand.net Accessed 15 October 2007.
- Imbamba SK Leaf protein content of some Kenya vegetables. East
African Agriculture and Forestry Journal 1973; 38: 246-251.
- Adams CA and M Richardson Nutritive
value of foods. USDA Home and Garden Bulletin 72, Washington DC, 1977.
- Gomez MI
Carotene content of some green leaf vegetables of Kenya and effects of
dehydration and storage on carotene retention. J. Plant Food 1981; 3: 231-244.
- Gomez MI The
evaluation of fruit and vegetable resources in the Machakos District in
relation to seasonal deficient and micronutrient deficiencies. Technical
Report IDRC 39, Ottawa, Canada, 1982.
- Schippers RR African indigenous vegetables: an overview of the cultivated species. Natural
Resources Institute / ACP-EU Technical Centre for Agricultural and Rural
Cooperation, Chatham, UK, 2000.
- International Vitamin A Consultative Group,
IVACG Maternal night blindness: extent and
associated risk factors. IVACG Statement. Washington, DC, 1997
- Khatry SK, Christian P, West KP and J
KatzEffect of maternal vitamin A or beta-carotene supplementation on
incidence of birth defects among Nepalese infants. In: Report of the
XVIII IVACG Meeting, Cairo, 1997. Washington, DC: IVACG, 1998: 87.
- Semba RD, Miotti P and JD Chiphangwi Maternal vitamin A deficiency and infant mortality in Malawi. J.
Trop. Paediatr. 1998; 44: 232-234.
- Wolf G The
regulation of retinoic acid formation. Nutr. Revs. 1996; 54: 182-184.
- World Health Organization Global prevalence of vitamin A deficiency. Micronutrient Deficiency
Information System (MDIS) Working Paper #2, WHO/NUT/95.3. Geneva: WHO, 1995.
- West KP Jr, Katz J and SK Khatry. Double blind, cluster randomized trial of low dose supplementation
with vitamin A or beta carotene on mortality related to pregnancy in Nepal. BMJ 1999; 318: 570-5
- Gebhardt SE and GT Robin Nutritive Value of Foods. U.S. Department of Agriculture,
Agricultural Research Service, Home and Garden Bulletin. 2002; 72: 7.
- Shantz EM and JH Brinkman Biological activity of pure vitamin A2. J. Biol.
Chem. 1950; 183: 467-471.
- Verhoef H and CE West Validity of the relative-dose-response test and the
modified-relative-dose-response test as indicators of vitamin A stores in
liver. Am. J. Clin. Nutr. 2005; 81: 835-839.
- Rice AL, Stoltzfus RJ, de Francisco A,
Chakraborty J, Kjolhede CL and MA Wahed Maternal
vitamin A or beta-carotene supplementation in lactating Bangladeshi women
benefits mothers and infants but does not prevent subclinical deficiency. J.
Nutr. 1999; 129: 356-365.
-
De Pee S, West CE, Muhilal, Karyadi D and JG
Hautvast Lack of improvement in vitamin A status with increased
consumption of dark-green leafy vegetables. Lancet 1995; 346: 75-81.
- National Research Council and National
Academy of Sciences Recommended dietary allowances,
10th ed. (Report of the Subcommittee on the Tenth Edition of the
RDAs, Food and Nutrition Board, Commission on Life Sciences). Washington, DC: National Academy Press. 1989: 85.
- Tanumihardjo SA Can lack of improvement in vitamin A status indicators be explained by little
or no overall change in vitamin A status of humans? J. Nutr. 2001; 131: 3316-3318.
- Arroyave G Alternative
strategies with emphasis on food fortification. In: West KP and A
Sommer (Eds). Delivery of oral doses of vitamin A to prevent vitamin A deficiency
and nutritional blindness . A state-of-the-art review. Geneva: UN ACC
Sub-committee on Nutrition. 1987: 87-91.
- West KP and A Sommer Delivery of oral doses of vitamin A to prevent vitamin A
deficiency and nutritional blindness: A state-of-the-art review. Geneva: UN ACC Subcommittee on Nutrition. 1987.
- Underwood BA Vitamin A prophylaxis programs in developing countries: past experiences and
future prospects. Nutr. Rev. 1990; 48: 265-274.
- De Pee S, West
CE, Permaesih D, Martuti S, Muhilal and JG Hautvast
Orange fruit is more effective than are dark-green, leafy vegetables in
increasing serum concentrations of retinol and beta-carotene in schoolchildren
in Indonesia. Am. J. Clin. Nutr. 1998; 68: 1058-1067.
- Haskell MJ, Jamil KM, Hassan F, Peerson JM,
Hossain MI, Fuchs GJ and KH Brown Daily consumption
of Indian spinach (Basella alba) or sweet potatoes has a positive effect
on total-body vitamin A stores in Bangladeshi men. Am. J. Clin. Nutr. 2004; 80: 705-714.
- Tanumihardjo SA Food-based
approaches for ensuring adequate vitamin A nutrition. Comp. Rev. Food Sci.
Food Safety. 2008; 7: 373-381.
- Howe JA and SA Tanumihardjo Carotenoid-biofortified maize maintains adequate vitamin A status
in Mongolian gerbils. J. Nutr. 2006; 136: 2562-2567.
- Tanumihardjo SA and Z Yang Carotenoids: epidemiology of health effects. In: Caballero
B, Allen L and A Prentice (Eds). Encyclopedia of Human Nutrition, 2nd ed. Oxford: Elsevier, 2005: 339-345.
- Penniston KL and SA Tanumihardjo The acute and chronic toxic effects of vitamin A. Am. J. Clin.
Nutr. 2006; 83: 191-201.
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