Research Article Open Access
Prevalence and Associated Factors of Vitamin A Deficiency among Children and Women in Senegal
Mane Hélène Faye1, Nicole Idohou-Dossou1, Abdou Badiane1, Anta Agne-Djigo2, Papa Mamadou DD Sylla1, Adama Diouf1, Amadou Tidiane Guiro1, Salimata Wade1
1Laboratoire de Recherche en Nutrition et Alimentation Humaine, Département de Biologie Animale, Faculté des Sciences et Techniques, Université Cheikh Anta Diop de Dakar. BP 5005, Dakar-Fann. Sénégal
2Équipe de Recherche Santé et Nutrition, Département Santé Communautaire, UFR Santé et Development Durable, Université Alioune Diop de Bambey, Diourbel
*Corresponding author: Mane Hélène Faye, Laboratoire de Recherche en Nutrition et Alimentation Humaine, Département de Biologie Animale, Faculté des Sciences et Techniques, Université Cheikh Anta Diop de Dakar. BP 5005, Dakar-Fann. Sénégal, Tel. No: +221 77 533 41 99, E-mail: @
Received: 24 April , 2020; Accepted: 8 June, 2020; Published: 21 July 2020
Citation: Nantchouang NAL, Kotue TC, Djouhou FM, Kansci G et al. (2020) Omega 3 and Azadirachta indica J. Seed Oil Inhibit Hemoglobin Polymerization and Modulate Erythrocyte Membrane Atpases in Sickle Cell Disease (SCD). J Nutrition Health Food Sci 8(2):1-7. DOI: 10.15226/jnhfs.2020.001176
AbstractTop
Background: Like many developing countries, Senegal does not have data on the extent of vitamin A deficiency (VAD) that is representative of its population. The present survey was conducted to fill this gap and to identify factors associated with VAD, prior to the introduction of a large-scale vitamin A oil fortification program.

Procedures: A nationwide representative cross-sectional survey involving 1887 children 12 to 59 months old and 1316 women of reproductive age (WRA) was conducted. Blood samples were collected and plasma concentrations of retinol (PR), C-reactive protein (CRP), and alpha-1-acidglycoprotein were measured. PR was adjusted for subclinical inflammation using the BRINDA regression methodology. Multivariate logistic regression was used to identify factors associated with VAD.

Findings: The adjusted prevalence of VAD (PR ≤ 0.7 μmol/L) in children was 15.3% and differed by age group, area of residence, and socioeconomic status and half of them had subclinical inflammation. Among WRA, VAD was low (2.3%) and 18.1% had vitamin A insufficiency (VAI). Pregnant women were more affected by VAI (28.4%) and Dakar had lower figures compared with other cities and rural strata. Prevalence of VAI decreased with increasing wealth quintile. In logistic regression, abnormal CRP, poverty, scarce consumption of poultry, oysters, melon, red palm oil, palm kernel oil, Saba senegalensis fruit pulp (Maad) and cowpea, frequent consumption of leeks and consumption of Leptadenia hastata leaves (Mbuum tiakhat), were associated with VAD in children. For women, lower socioeconomic status, fair or poor health status and anemia were negatively associated with VAI.

Conclusions: In Senegal, VAD is a moderate public health problem in children and slight among women. Particular attention should be paid to children older than 23 months, pregnant women, rural populations, and poorest households. Nutritional interventions should be implemented alongside morbidity prevention and control.

Keywords: vitamin A deficiency, children 12-59 months, women of reproductive age, Senegal.
IntroductionTop
Vitamin A is an essential nutrient involved in several biological processes including metabolism, hematopoiesis, embryogenesis, immune response, vision, reproduction, and growth [1]. Vitamin A deficiency (VAD) occurs mainly with low dietary intakes, impaired absorption of vitamin A or provitamin A carotenoids, and/or demand increased due to infections or life cycle. The consequences of VAD include the development of night blindness and ocular clinical signs, which can lead to full vision loss; anemia; and low resistance to infections, which increases the risk of morbidity and mortality [2-3].

Children under five years and Women of Reproductive Age (WRA) are the greatest vulnerable groups at risk for VAD according to the WHO [2]. Subclinical VAD affects more than 30% of under five year old children globally with the highest prevalence rate observed in sub-Saharan Africa (48%) [4]. Recent data suggested that VAD is the underlying cause of 2% of all deaths in this age group and the leading cause of preventable blindness. West African countries with published VAD figures indicated a public health problem in children with data varying from 7.3% to 63.1% in Liberia, Sierra Leone, Gambia, Ghana, Ivory Coast, Burkina-Faso, Nigeria, Benin, Guinea-Bissau and Mali [5-14]. WRA, especially pregnant women are also affected (19.1 million) and Africa represents over 20% of the global burden [2].

In 2009, Senegal, as in most developing countries, had limited data on the magnitude of VAD, which were either estimations or sub-national, outdated, and/or based on non-biochemical indicators. Using impression cytology, VAD was found in 11.4% of children aged 2-6 years in the rural area of the groundnut belt of Senegal [15]. Outlined biochemical results in children indicated a VAD public health problem in the Department of Linguère (Louga region) and in Bambey, Kebemer, and Koungheul with prevalence of 71.5% and 26.1% in 1993 and 1997, respectively [16-17]. According to MI/UNICEF and the WHO, prevalence of VAD was estimated to be 61% (2004) and 37% (2005) [2, 18]. In women, statistics were disparate between geographical areas and over time, ranging from 57.1% to 2.5% between 1997 and 2006 while WHO estimated a national prevalence of 19.4% among pregnant women in 2009 [2, 18-20]. Night blindness was reported to affect 2% of women in Senegal [21]. Therefore, there was a real need for more accurate and representative data prior to the introduction of a large-scale vitamin A oil fortification program. To effectively address VAD at the population level, biological data on its extent were needed.

Several indicators of vitamin A status and their usefulness were already described [22-23]. Plasma retinol (PR), even if not reliable in diagnosing VAD in individuals due to its homeostatic control, is informative in assessing the severity of VAD among populations. However, retinol is altered during inflammation or infection by as much as 25%, leading to inaccurate estimations of deficiency in populations with high prevalence of infection [23-25]. As infection and inflammation are accompanied by an increase in the plasma concentration of acute phase proteins, their measure should be performed to adequately interpret PR concentration.

Thus, the aim of this survey was to assess, for the first time, the national prevalence of VAD and its determinants among children 12 to 59 months and WRA in Senegal.
MethodsTop
Study Design and Population
A nationwide representative cross-sectional survey, involving children 12 to 59 months and WRA 15 to 49 years, was conducted during the dry season, from April to May 2010. According to food consumption and socioeconomic patterns, Senegal was stratified into 4 areas: Urban Dakar, Other urban cities, Rural 1 (rural areas of Tambacounda, Kedougou, Kolda, Sedhiou, and Ziguinchor regions) and Rural 2 (rural areas of Matam, Saint Louis, Louga, Thies, Diourbel, Fatick, Kaolack, Kaffrine, and Dakar). A twostage stratified cluster sampling procedure with probability proportional to size was carried out to randomly select 1810 households from 57 clusters. The sample size calculation for women was based on prevalence of VAD during wet season (7%) reported by Gueye [20] in rural women of Sedhiou, southern Senegal. Considering a design effect of 2.9 and a precision of 5.0%, the minimal sample size required was 915 women. Using the above parameters and considering a prevalence of VAD of 61% [18], the sample size needed was 1104 for children aged 12 to 59 months. The survey protocol was approved by the ethical committee of the Senegalese Ministry of Health (CNERS). Women and children were eligible if informed written consent was provided by the heads of households, women, and children’s mothers or caregivers.

Data Collection Procedures
Questionnaires were used to collect subjects’ socioeconomic, socio-demographic, food consumption, and health history data. Socioeconomic data included information on housing (occupancy status, drinking water source, type of toilet facilities, type of fuel used for cooking, type of household lighting) and ownership of durable goods (household equipment and livestock). These data were analyzed to generate a household’s socioeconomic status indicator (wealth quintile) consisting of 5 categories (poorest, poor, intermediate, relatively wealthy, and wealthiest). Main sociodemographic data collected were physiological status (pregnant, breastfeeding, non-pregnant/ non-breastfeeding) for women and gender and age for children. Children’s food consumption habits (breastfeeding and complementary feeding practices) were reported as well as food frequency data and women’s knowledge on vitamin A-rich foods. Health status and presence of clinical signs of VAD among children and women were carried out by physicians based on their medical history and physical examination. In addition, anemia status of children and women was investigated.

Blood Collection and Biological Measurement
Blood collection was performed by medical staff. Ten (10) and 5-7 milliliters of blood were drawn from women and children, respectively, by venipuncture using a single-use syringe, and metal-free vacuum collection tube containing lithium heparin as anticoagulant (Sarstedt). Hemoglobin (Hb) concentrations were measured on a drop of whole blood using an HemoCue® 201+ portable device (HemoCue AB) while the remaining sample was centrifuged at 3200 rpm for 12 minutes and plasma stored at -20°C in the field and kept at -80 °C in the laboratory until analysis. Plasma handling was done away from dust, under minimal light, and wrapped with aluminum foil to protect lightsensitive compounds from degradation. Samples were analyzed for plasma retinol (PR), C-reactive protein (CRP) and alpha-1 acid glycoprotein (AGP) in the Laboratoire de Recherche en Nutrition et Alimentation Humaine, Université Cheikh Anta Diop, Dakar, Senegal.

PR analysis was performed by high performance liquid chromatography using a methodology previously described [26] using a Spectra SYSTEM (Thermo Electron SAS) consisting of an SCM1000 vacuum membrane degasser, a pump P1000XR, an autosampler AS3000, a UV6000LP detector, and a SN 4000 module.

CRP and AGP concentrations were measured by immunoturbidimetry using a Biosystems A15 automatic analyzer (Biosystems S.A.) with Biosystems kit reagents.

Cutoffs
PR concentration < 1.05 μmol/L was used to define vitamin A insufficiency (VAI) in women and PR ≤ 0.7 μmol/L was used to define VAD both in women and children [22-23]. Inflammation
Figure 1: Flow chart of children 12 to 59 months and WRA recruited into a study to evaluate the national prevalence of VAD in Senegal, 2010
status was defined as CRP > 5 mg/L and/or AGP > 1 g/L [25]. Anemia was defined by Hb concentration < 110 g/L in children and pregnant women and Hb concentration < 120 g/L in nonpregnant women [27].

Adjustment of PR Concentration for Inflammation Using BRINDA Methodology
PR concentration was adjusted for subclinical inflammation using the regression correction approach developed by the BRINDA project as previously described [28-29] and prevalence of VAD was derived from those values. Briefly, adjusted PR values were obtained by subtracting the influence of CRP and AGP as follows: Retinoladjusted = retinolunadjusted – β1 (CRPobs - CRPref) – β2 (AGPobs - AGPref). In this equation, β1 and β2 are regression coefficients of CRP and AGP, respectively, obs is the individual observed value and ref is the reference value. Retinol, CRPobs, CRPref, AGPobs and AGPref are on natural logarithm scale. Internal reference values from our dataset (maximum value of the lowest CRP or AGP decile or 10th percentile obtained) were used. Unlogged CRPref was 0.1 mg/L both for children and women while AGPref was 0.65 g/L and 0.55 g/L in children and women, respectively. Adjustments were only applied to individuals with either CRP concentrations˃ CRPref, AGP concentrations˃ AGPref or both. PR-adjusted values were back-transformed before applying cutoffs.

Statistical Analysis
Statistical analysis was performed using SPSS 15 (SPSS for Windows) and STATA/SE version 11.0 (STATA Corporation). Data were weighted for national representativeness of the results. Categorical variables were expressed as percentages, and continuous variables were expressed as means ± SD, except for CRP which was not normally distributed. Plasma concentrations of CRP were log-transformed and expressed as geometric means with 95% confidence interval [CI]. Student’s t-test and analysis of variance (ANOVA) associated to a Bonferroni correction were used to compare means. Pearson’s chi-squared was used to compare percentages. Comparisons were also done between age and sex groups in children, according to their physiological condition in women (pregnant, breastfeeding, non-pregnant/ non-breastfeeding), and by area of residence for both children and women. Relation between PR and inflammation biomarkers was studied using Pearson’s correlation coefficient (r). Multiple logistic regression model was used to assess association of socioeconomic, dietary, and health factors with VAD. For all statistical analyses, a significance level of 0.05 was used.
ResultsTop
Characteristics of the Study Population
In this study, 1316 WRA and 1887 children aged 12 to 59 months were targeted and PR concentration was measured on 1082 WRA and 1418 children [Figure 1]. Sociodemographic and health-related characteristics of the study population are presented in Table 1.
Table 1:Sociodemographic and health related characteristics of the study population

n

%

Children

Age group, months

Dec-23

462

24.2

24-35

485

25.8

36-47

480

26.2

48-59

442

23.8

Gender group

Girls

948

50.1

Illness (within last 15 days)

Fever

395

65.7

Diarrhoea

119

25.1

Cough/ breathing trouble

198

40.1

VAS (within last 6 months)

1079

78.5

Deworming (within last 6 months)

1068

77.7

Anemia

967

66.1

Women

Age group, years

15-19

286

20.5

20-24

283

22.5

25-29

199

16.2

30-34

187

13.7

35-39

145

10.7

40-44

121

10.2

45-49

92

6.1

Physiological status

Pregnant

100

8.8

Lactating

270

25

NPNL1

713

66.2

Night blindness

18

3.9

Clinical signs of VAD

60

8

Anemia

498

47.5

1NPNL: Non pregnant-Non lactating

Among the children, the mean age was 34.3 ± 13.0 months. Their proportion was almost equal between age groups while girls represented 50.1% of the children. Within the 15 days prior to the survey, fever, diarrhea, and cough/breathing trouble related to illness were reported in 65.7%, 25.1%, and 40.1% of children, respectively. Coverage of vitamin A supplementation in children within the last 6 months preceding the survey was 78.5% (n=1079) with disparities among strata (Dakar: 20.5%; Other cities: 84.4%; Rural 1: 51%; Rural 2: 95.2%). Among these, 77.7% were dewormed in the same period. The breastfeeding rate among children under 2 years was 98.1% (n=156). No case of night blindness was observed among the children. Mean age of WRA was 28 ± 9 years. Women aged 20-24 (22.5%) and 15-19 years (20.5%) were the most represented. The sample included 8.8% pregnant, 25% lactating, and 66.2% non-pregnant/nonlactating women (NPNL). Night blindness affected 3.9% (n=18) of women in their last pregnancy that resulted in a live birth during the past 3 years. Clinical signs of VAD were reported in 8% (n=60) of women. Anemia affected 66.1% (n=967) of children and 47.5% (n=498) of women.

Subclinical Inflammation among the Study Population
Inflammation was widespread and involved 1 out of 2 children, regardless of gender. Prevalence of inflammation decreased with age and the children aged 12-23 months and 24- 35 months were the most affected groups [Table 2]. Among the women, over one quarter were affected by inflammation with significant differences according to their physiological status and the area of residence. The prevalence of inflammation in women was higher in Dakar compared to other cities and Rural 1 (P < 0.01).

Plasma Retinol Concentration and Prevalence of vitamin A Deficiency Among Children
PR concentration was normally distributed among children and its mean value was 0.90 ± 0.26 μmol/L [min: 0.16; max: 1.85] [Table 3]. According to gender, mean PR was higher in girls compared with boys (P < 0.01). PR concentration was significantly higher in children aged 12-23 months compared with those in 24-35 (P < 0.01), 36-47 (P < 0.001), and 48-59 (P < 0.05) months groups. According to their area of residence, no significant difference was observed in PR concentration between urban strata. The same scheme was observed between rural strata. However, mean PR concentration of children in urban strata were higher than in rural strata (P < 0.001). In addition, PR concentration increased meaningfully with socioeconomic status (P < 0.05).

According to inflammation status, both CRP and AGP were negatively and significantly associated with PR of children (CRP: r=-0.1162, P < 0.001; AGP: r=-0.1790, P < 0.001). Inflammation adjustment was done on PR using the BRINDA regression methodology. After adjustment with inflammation, mean PR concentration of children significantly increased (0.9 ± 0.26 vs. 0.99 ± 0.28 μmol/L, P < 0.001) and the difference observed between groups (gender, age, area of residence, and socioeconomic status) persisted. The prevalence of VAD after inflammation-adjustment in 12-59 months aged children was 15.3% [Table 3] with 0.1% severe cases [Table 5]. Prevalence of VAD was comparable between gender groups but significantly higher in 24-35 and 36-47-months aged children compared to
Table 2: Extent of subclinical inflammation among children and women1

Stage of inflammation2

n

Any inflammation3

Incubation

Early convalescence

Late convalescence

Children

National

1434

50.1

6.2

12.7

31.2

Gender

Male

712

52.5

7

11.3

34.1

Female

722

47.7

5.3

14.1

28.3

Age group, months

23-Dec

330

65.5a

6.7

20.6

38.2

24-35

359

54.8b

6.2

10.7

37.8

36-47

376

46.0c

7.9

12.8

25.3

48-59

132

36.5d

3.9

7.8

24.7

Area of residence

Dakar

190

58.7a

16.6

14.9

27.3

Other cities

310

42.0b

5.4

12.7

24

Rural 1

382

43.0c

1.8

8.2

33

Rural 2

552

52.7a, b, d

5

13.2

34.4

Women

National

1082

27.7

10.8

6.6

10.3

Physiological status

Pregnant

99

26.9a

20.6

2.1

4.2

Lactating

267

34.4a, b

9

9.5

15.9

NPNL4

707

25.8b, c

10.4

6.2

9.1

Area of residence

Dakar

293

33.3a

14.5

7

11.8

Other cities

182

29.8a, b

7.7

9

13.2

Rural 1

217

16.3c

3.4

8

4.9

Rural 2

390

22.8b, d

9.1

4.9

8.7

1Values are %. For each indicator, values between category of groups (in columns) with different superscript letters (a, b, c and d) are significantly different, P < 0.05

2Stage of inflammation: no inflammation (CRP≤ 5 mg/L and AGP≤ 1 g/L); incubation (CRP> 5 mg/L and AGP≤ 1 g/L); early convalescence (CRP> 5 mg/L and AGP> 1 g/L); late convalescence (AGP >1 g/L and CRP≤ 5 mg/L)

3Any inflammation: CRP> 5 mg/L and/ or AGP> 1 g/L

4NPNL: Non pregnant-Non lactating

those aged 12-23 months. According to areas of residence, Rural 1 and Rural 2 had comparable figures but both presented higher prevalence of VAD than urban strata (P < 0.001). Children in the poorest households had a higher prevalence of VAD than in other household wealth categories.

Plasma Retinol Concentration and Prevalence of Vitamin A Deficiency among Women
Overall, mean PR concentration of WRA was 1.43 ± 0.44 μmol/L [min: 0.355; max: 3.851] [Table 4]. In WRA, weak but significant and negative correlation was observed between PR and CRP (r=-0.069, P=0.042) while no relationship was observed with AGP (r=0.033, P=0.274). Because of this weak relationship between inflammation and retinol in women, PR was not adjusted and the prevalence of VAD was estimated from non-adjusted values. Vitamin A insufficiency (VAI) was present in 18.1% of women among which 2.3% had VAD and 15.7% marginal vitamin A status [Table 5]. Mean PR was associated with physiological status and was lower in pregnant women compared with lactating (P = 0.002) and NPNL women (P < 0.001). Thus, the prevalence of VAI was higher in pregnant women (28.4%), comparable to lactating women but significantly different from NPNL women (P < 0.001). Furthermore, when women were separated into 2 groups (Pregnant vs Non-pregnant), VAI was higher in pregnant women (28.4% vs.17.2%, P < 0.01). According to the area of residence, PR concentration was significantly higher in urban Dakar (P < 0.001). Consequently, prevalence of VAI was significantly different among strata, lower in Dakar compared with others cities (P < 0.01) and rural strata (P < 0.001). Significant differences were also observed using socioeconomic status and consequently prevalence of VAI decreased with increasing wealth quintile from 37% in the poorest to 9.1% in the wealthiest (P < 0.001).

Factors associated with vitamin A deficiency among children
Logistic regression analysis [Table 6] showed that poverty status was associated with children’s risk of VAD. Indeed, children from poorest, poor, and intermediate socioeconomic status households had 5.64, 2.33 and 4 times greater risk of VAD, respectively (P < 0.01) than their wealthiest peers. Incubation phase of inflammation was also a risk factor for low PR in this population group. Regression from dietary patterns showed that
Table 3: Plasma retinol concentrations and VAD prevalence according to gender, age group, area of residence and socioeconomic status among children1

Plasma retinol (μmol/L)

VAD (%)

n

Unadjusted

Adjusted2

Unadjusted

Adjusted

National

1418

0.9±0.26

0.99±0.28

24.5

15.3

Gender

Girls

702

0.88±0.24a

0.97±0.26a

26.4

16.3

Boys

716

0.92±0.27b

1.0±0.3b

22.6

14.3

Age group, months

23-Dec

324

0.96±0.28c

1.1±0.3c

19.4c

9.9c

24-35

353

0.89±0.26d

0.98±0.29d

26.6d

17.3d

36-47

374

0.87±0.25d

0.94±0.27d

30.2e

17.9d

48-59

366

0.90±0.23d

0.97±0.25d

20.9c, d

13.1c, d

Area of residence

Dakar

190

0.97±0.24a

1.1±0.25a

15.0a

6.9a

Other cities

308

0.98±0.26a

1.1±0.28a

14.6a

8.2a

Rural 1

377

0.87±.25b

0.95±0.27b

27.0b

20.0b

Rural 2

543

0.86±0.25b

0.95±0.28b

29.8b

18.4b

Socioeconomic status

Poorest

298

0.82±0.23a

0.89±0.25a

33.6a

25.3a

Poor

346

0.87±0.25b

0.95±0.27b

26.5b

15.6b

Intermediate

313

0.89±0.27b

0.98±0.3b

29.1b

20.7b

Wealthy

263

0.96±0.24c

1.05±0.26c

14.7c

5.7c

Wealthiest

193

1.0±0.26c

1.10±0.28c

14.3c

5.5c

1Values are mean±SD or %. For each indicator, values between category of groups (in columns) with different superscript letters (a, b, c and d) are significantly different, P < 0.05 (t-test or ANOVA for comparisons of means; Pearson chi2 test for comparison of prevalence)

2Adjusted using the BRINDA methodology [20-21]

Table 4: Plasma retinol concentrations and prevalence of VAI according to physiological status, area of residence and socioeconomic status among women1

n

Plasma retinol, μmol/L

VAI (%)

National

1082

1.43±0.44

18.1

Physiological status

Pregnant

99

1.26±0.38a

28.4a

Lactating

267

1.42±0.47b

22.3a, b

NPNL2

707

1.46±0.43b

15.2b, c

Area of residence

Dakar

293

1.57±0.42a

7.7a

Other cities

182

1.4±0.37b

16.8b

Rural 1

217

1.27±0.42b, c

31.8c

Rural 2

390

1.3±0.42c

28.3c

Socioeconomic status

Poorest

193

1.2±0.4a

37.0a

Poor

174

1.3±0.4a

29.8a, b

Intermediate

228

1.41±0.47a, b

20.9b, c

Wealthy

219

1.46±0.39b, c

14.2d

Wealthiest

264

1.54±0.41c

6.9e

1Values are mean±SD or %. For each indicator, values between category of groups (in columns) with different superscript letters (a, b, c and d) are significantly different, P < 0.05

2NPNL: Non pregnant-Non lactating

rare or no consumption of foods rich in preformed vitamin A, vitamin A precursors and or dietary fats was predictive of VAD (poultry, oysters, melon, red palm oil, palm kernel oil). On the other hand, their frequent consumption or simple consumption were found to have significant protective effects (P < 0.05) on children’ s VAD (Saba senegalensis fruit pulp, leeks) at the exception of Leptadenia hastata leaves (OR=1.91). Only rare consumption of cowpea was found to be protective for VAD (OR=0.47).

Factors Associated with Vitamin A Insufficiency among Women
Among women, the odds of VAI increased with lower socioeconomic status. Hence, compared with women from the wealthiest households, those from relatively wealthy, intermediate, poor and poorest households had 2.53, 5.32, 5.95, and 8.44 greater risk of VAI, respectively [Table 6.] In addition, fair (OR=2.51) and poor (OR=7.96) health status as well as anemia status (OR=1.88) were negatively associated with VAI in women.
Table 5: Levels of vitamin A deficiency (VAD) among Senegalese children and women

Prevalence of vitamin A deficiency

n

%

Children1

1418

Normal status

1210

84.7

Marginal VAD

207

15.2

Severe VAD

1

0.1

Women2

1082

Normal status

861

81.9

Marginal status

192

15.7

VAD

29

2.3

1Normal status: PR>0.7 μmol/L, Marginal VAD: 0.35<PR≤0.7 μmol/L), Severe VAD: PR ≤0.35 μmol/L

2Normal status: PR≥1.05 μmol/L, Marginal VA status: 0.7<PR<1.05 μmol/L, VAD: PR≤ 0.7 μmol/L

DiscussionTop
Nationally, data from the present study revealed that VAD was a moderate public health problem in children aged 12 to 59 months according to the WHO classification criteria using PR as the indicator [23]. Our findings were lower than the estimations of 37% and 61% reported by the WHO and MI/UNICEF, respectively, probably due to the methodology based on regression model estimates using member countries reported studies [2, 18]. The prevalence of VAD observed in our study seems to be lower than those of all West African countries with published national statistics with the exception of Liberia (7.3%), i.e., Sierra Leone (17.4%), Gambia (18.3%), Ghana (20.8%), Ivory Coast (24.1%), and Nigeria (29.5%) [5-9, 11]. However, comparison should be done with caution because those data were mainly based on RBP measurement instead of PR concentration as recommended by the WHO for population surveys and used different methods of correction for inflammation, when applicable. Nevertheless, as observed in bivariate analysis, VAD was mild among children 12-23 months and those from urban strata but severe among children living in the poorest wealth quintile households. These dissimilarities might be linked to the higher rate of breastfeeding (98.1%) in 12-23 months of this study associated with adequate vitamin A status in lactating women and differences in socioeconomic status between urban and rural areas. When comparing unadjusted VAD with subnational figures reported in 1997 (26.1%), it seems that prevalence of VAD has not substantially decreased over the past decade despite the implementation of vitamin A supplementation (VAS), the only large-scale strategy implemented at the time of the survey which started since 1999 among children under 5 years. VAS coverage has declined between 2005 (75%) [21] to present (63%) [30] and its rate stayed below the target of the Senegalese VAS program (95%) [31]. This situation highlights the need to strengthen the national VAS program and consolidates the VA cooking oil fortification program as a control strategy for VAD with focus on children older than 23 months, children from rural areas, and those living in the poorest households. In less affected population groups, VAD control programs should consider that vitamin A might be provided in excess due to overlapping programs and might cause hypervitaminosis A in the long-term [32], meaning that inclusive population monitoring is needed with biomarkers more sensitive than PR concentrations [33-34].

In multivariate analysis, poverty, abnormal CRP, and scarce or no consumption of several vitamin A food sources were found to be predictive of VAD risk in Senegalese children. Indeed, poor socioeconomic status could have a negative impact on food security by limiting access to sufficient and nutritious food, thus compromising the satisfaction of nutritional requirements of the population [35-36]. It could also affect financial access to adequate care. Moreover, morbidity prevention and control should be consolidated, regarding the high occurrence of illness observed in children that was corroborated by high prevalence of inflammation and the association between VAD and abnormal CRP concentration. Alongside these efforts, nutrition education promoting adequate dietary intake of preformed and / or vitamin A precursors rich foods such as poultry, oysters, melon, leeks, red palm oil and Saba senegalensis fruit pulp should be considered. The risk of VAD associated with consumption of Leptadenia hastata leaves reported to be rich in β-carotene [37] might be related to the low bioavailability associated with the matrix in which the provitamin carotenoids are incorporated, antinutritional factors, or poverty. In this study, cowpea’s rare consumption was found to have a protective effect on VAD. Given the higher protein content of cowpea (20% to 40%), its frequent consumption might reduce the activity of the enzyme carotene dioxygenase which is involved in β-carotene absorption [38], explaining a protective effect in those consuming cowpeas rarely. The protective effect of palm kernel oil on the risk of VAD can be explained by the known improvement effect of dietary fats on vitamin A and provitamin A carotenoid absorption. In addition, even if lacking vitamin A precursors, palm kernel oil could be contaminated from palm fruit pulp during traditional transformation processes. Otherwise, this association needs further investigation.

Among Senegalese women, prevalence of VAD was low (2.3%), depicting a minor public health problem, while 15.7% of them was at risk of VAD. The prevalence of VAD is consistent with the 2.5% found during dry season in the rural area of Sedhiou in 2006 [20]. It is also comparable to Sierra Leone (2.1%) but slightly over the data from Ghana (1.5%) and Gambia (1.8%) [6-8]. Pregnant women were most affected by VAI, probably due to either hemodilution or the 60% additional vitamin A requirements needed to ensure normal fetal growth, to provide a limited reserve in the fetal liver, and to maintain their own tissue growth [39]. Biochemical results were in line with the reported extent of night blindness among women (3.9%), greater than the
Table 6: Factors associated with VAD among children and women in Senegal

Odds ratio

IC à 95%

P value

Children

Socioeconomic status

Wealthiest

1

Intermediate

4

2.10-7.64

0.000

Poor

2.33

1.19-4.57

0.013

Poorest

5.64

2.97-10.7

0.000

Inflammation/Infection1

Non

1

Oui

2.04

1.26-3.3

0.004

Food consumption frequency2

Poultry

Frequent

1

Rare

1.78

1.14-2.78

0.011

No

2.05

1.08-3.89

0.027

Oysters

Frequent

1

Rare

3.03

1.21-7.53

0.017

Melon

Frequent

1

Rare

2.3

1.35-3.92

0.002

Saba senegalensis fruit pulp (Maad)

Non

1

Rare

0.5

0.29-0.85

0.011

Leeks

No

1

Frequent

0.1

0.014-0.83

0.033

Leptadeniahastata leaves (Mbuumtiakhat)

No

1

Yes

1.91

1.25-2.92

0.003

Cowpea

Frequent

1

Rare

0.47

0.27-0.79

0.005

Red palm oil

Frequent

1

No

1.9

1.21-2.98

0.005

Palm kernel oil

Frequent

1

No

2.7

1.25-5.83

0.011

Women

Socioeconomic status

Wealthiest

1

Relatively wealthy

2.53

1.26-5.04

0.008

Intermediate

5.32

2.80-10.08

0.000

Poor

5.95

3.08-11.49

0.000

Poorest

8.44

4.46-15.98

0.000

General health status

Excellent

1

Fair

2.51

1.5-4.19

0.000

Poor

7.96

2.2-28.82

0.002

Anemia

No

1

Yes

1.88

1.33-2.65

0.000

1Incubation (CRP> 5 mg/L and AGP≤ 1 g/L)

2Food consumption frequency: Frequent (at least 1 time a day or 1 to 3 times per week); Rare (1 time a month or less); No (never consumed at the period of the survey)

prevalence of 2% found among Senegalese women in 2005 [21] but below the cutoff point of 5% defining a public health problem [40].

As for children, poverty was a predictive factor of VAI, the lower the socio-economic status, the higher the risk of VAI. An increased risk of insufficient vitamin A intakes associated with lower socioeconomic status was reported in WRA in Vietnam [41]. Anemia was found to be associated with VAI in Senegalese women. This result supports the well-known relationship between VAD and anemia that has been documented [42-43]. Analogous findings were observed among WRA in Cameroon and Ivory Coast as well as pregnant women in Nepal, India, Iran, Bangladesh, China, and Brazil [44-50]. Even if potential mechanisms by which vitamin A influences anemia have been proposed [43], the pathogenesis of this association remains unclear. However, VAD is known to impair mobilization of iron stores, decreasing iron supplies to the bone marrow and reducing hemoglobin synthesis [51]. Concerning the increased risk of VAI with fair or poor health status, it was likely due to the synergistic relationship between altered vitamin A status and occurrence of infections. This calls to enhanced management of acute inflammation and / or infection particularly, as suggested by the correlation, even weak, between PR and CRP.
ConclusionTop
In conclusion, this survey, the first nationally-representative in Senegal, showed that vitamin A deficiency is a moderate public health problem in children and marginal among women. But particular attention must be paid to children over 23 months, pregnant women, rural populations, and the poorest households who are the most vulnerable. Based on reported predictors of VAD among our study population, improvement of VAD in Senegal requires a multiple approach strategy: 1) strengthening the VAS program in order to prevent inflammation and infection related illnesses among children; 2) preventing and controlling anemia among women; 3) implementing the vitamin A fortification program in order to reach high geographical coverage and to make accessible adequately fortified oil, especially for the most vulnerable. This also implies proper monitoring and evaluation to reduce risk of vitamin A excess among groups less affected by VAD; and 4) reinforcing nutrition education by promoting local vitamin A rich products.
AcknowledgementsTop
The authors appreciate the support of the Comité Sénégalais pour la Fortification des Aliments en Micronutriments (COSFAM) and Nutrition International (Ex Micronutrient Initiative). The authors thank Professor Sherry A. Tanumihardjo for editing the manuscript.
Author ContributionsTop
MHF participated in data management, performed statistical analysis and drafted the manuscript. SW, ATG, and NID participated in the conceptualization of the study. NID supervised vitamin A assays. AD and AAD participated in data collection and data management. AB and PMDDS participated in data analysis. All the authors reviewed the manuscript and approved its final submitted version.
DeclarationsTop
Conflict of Interest
The author(s) declared no conflicts of interest with any financial/research/academic organization with regards to the research, authorship, and/or publication of this article.

Ethical Approval
The protocol was approved by the ethical committee of the Senegalese Ministry of Health (CNERS) under the reference number SEN 38/08 ITA-COSFAM. Fully informed written consent has been obtained from survey participants.
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