Introduction

Breast milk is one of the many distinct forms of Bio-fluid that can be contaminated with mycotoxins1,2,3,4,5. The fungi that produce these secondary metabolites are primarily Fusarium, Aspergillus, and Penicillium6,7. They may be ingested by tainted animals and agricultural crops, which subsequently manifest in breast milk and result in health issues such as nervous system disorders and malignancies of the urinary tract, liver, kidneys, and lungs8,9. Aflatoxins (AFs), one of the most important types of mycotoxins, can enter the body via the consumption of contaminated food products by mothers and appear in their milk10,11. Moreover, exposure to aflatoxins is also associated with several health problems, including immunological suppression and malnutrition10,12,13.

Milk and milk products from dairy cows that eat feed contaminated with aflatoxin B1 (AFB1) can include aflatoxin M1 (AFM1) and aflatoxin M2 (AFM2), which are hydroxylated metabolites of AFB11. Some of the detrimental effects of AFM1 include hepatotoxicity, estrogenicity, reproductive problems, cutaneous irritation, developmental impairment, and carcinogenicity (liver cancer)14.

The International Agency for Research on Cancer has classified AFM1 as a category 1 carcinogen (carcinogenic to humans)15,16. AFM1 concentrations in milk for babies and children should not exceed 25 ng/L, according to recommendations from the European Union (EU)17. Infants are considered to be more prone to AFM1 because of their immature detoxification systems and higher food consumption relative to body weight18,19. Aflatoxin M1 is one of the most significant pollutants in human milk owing to its negative effects on baby health, including its ability to induce cancer, mutation, and teratogenicity14,20. Other adverse effects on infant health include immunosuppression, weight loss, and developmental abnormalities21. A crucial time in a person's life is infancy, and breast milk is typically the main source of sustenance for children22, including hormonal and immunological components that help shield infants from infectious illnesses23. Infant detoxification rates are lower than those of adults because of their faster pace of growth and lower body weight24. However, an increase in detoxification by oxidation and hydrolysis has been reported in infants after four weeks of age25,26. As a result, mycotoxins such as AFM1 are more dangerous to newborns than adults14.

A wide range of AFM1 concentrations in breast milk has been measured in several sub-African countries, including 11 studies from the western Africa region27,28,29,30,31,32,33,34,35,36,37, eight studies from eastern Africa34,38,39,40,41,42, seven studies from northern Africa43,44,45,46,47,48,49, and two studies from southern Africa50,51. The highest concentration was found in Ghana (369 ng/l)34, and the lowest concentration was found in Sierra Leone (0.8 ng/l)52. Despite several studies on the prevalence and concentration of AFM1 in human breast milk, no systematic meta-analysis or meta-regression studies on the African scale have been performed. Hence, the current study was devoted to performing a systematic review, meta-analysis, and meta-regression regarding the concentration and prevalence of AFM1 in human breast milk, considering socioeconomic indices and amounts of precipitation in Africa. Additionally, the carcinogenic risk to infants’ consumers was estimated using a Monte Carlo simulation assessment.

Methods

Protocol and eligibility criteria

This review was done to determine the prevalence and concentration of aflatoxin M1 in breastfeeding mothers with breast milk in Africa in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 standard (Additional File 1)53.

Studies that measured the level of Aflatoxin M1 exposure or contamination of human breast milk in lactating women in Africa were included. We used the PICOS criteria for eligibility54; the populations were lactating women in Africa, the exposure was aflatoxin in breast milk, the context was studies done in Africa, and the study design was observational studies that examined Aflatoxin M1 levels of contamination with breast milk using different diagnostic mechanisms, such as HPLC and ELISA. The articles included in this review were available in English and were published until August 3, 2023. Case series, reports, reviews, commentaries, and editorials were excluded from this review (Fig. 1).

Figure 1
figure 1

Map of available studies on concentration of aflatoxin M1 in breast milk in Africa, 2023.

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Information sources

We performed an electronic literature search using legitimate databases and website platforms such as Web of Science, Embase, Scopus, MEDLINE (OVID), Google Scholar, and PubMed. We also searched for different university institutional repository sites and conducted a direct Google search.

Search strategy

The search was performed using a combination of Boolean logic operators (AND, OR, NOT), Medical Subject Headings (MeSH), and keywords. The search strategy for advanced PubMed includes "aflatoxin M1 "[MeSH Terms] AND ("milk, human"[MeSH Terms] OR ("milk"[All Fields] AND "human"[All Fields]) OR "human milk"[All Fields] OR ("breast"[All Fields] AND "milk"[All Fields]) OR "breast milk"[All Fields]) AND "africa"[MeSH Terms]. The search strategies for Web of Science, Medline, Scopus, and Embase are presented in the supplementary file (Additional File 2).

Study selection

The database search results were consolidated, and duplicate articles were manually removed using a reference management application (Endnote version X8). The titles and abstracts of the papers were carefully evaluated. Two writers (JY and IM) independently reviewed the full texts of the remaining publications to determine their eligibility based on the predetermined inclusion and exclusion criteria. The objectives, methodology, diagnosis method, population, and significant findings (prevalence and concentration of aflatoxin M1 in breast milk in Africa and its implications for the interface of agriculture and health) of the full-text studies in English were then reviewed further. All authors agreed to handle any questions developed during the extraction process, and the final agreement was finalized with the assistance of the authors (JY, AD, AE, and IM). The PRISMA statement flow diagram was used to represent the research selection process.

Data extraction

After identifying articles that met the inclusion criteria, three authors (AD, AE, and IM) independently extracted the data using Microsoft Excel 2016. Different variables of interest were considered in the extraction and are presented in the table. The accuracy of data extraction was verified by comparing the results obtained by the two authors55. The information used for meta-analysis of the included articles was extracted, which included the mean concentration of aflatoxin M1 in breast milk (N), frequency of the occurrence of aflatoxin M1, measure of associations with 95% CI, and effect size.

Data analysis

The primary outcome of this meta-analysis was the level of aflatoxin M1 contamination in breast milk among lactating women in Africa. AFM1 is the parent molecule of aflatoxin, which is hydroxylated in the liver and possibly in the human breast by cytochrome oxidase enzymes and then excreted into breast milk as AFM1 during lactation via mammary alveolar epithelial cells. AFM1 can contaminate human breast milk directly from dairy products or by carryover from the parent molecule. The secondary outcome of interest was the mean concentration of aflatoxin M1 in breast milk measured in different SI units56.

Risk of bias (ROB) assessment

The Newcastle–Ottawa Scale (NOS) is an ongoing collaboration between the Universities of Newcastle, Australia and Ottawa, Canada. It was developed to assess the quality of nonrandomized studies with its design, content and ease of use directed to the task of incorporating the quality assessments in the interpretation of meta-analytic results. A 'star system' has been developed in which a study is judged on three broad perspectives: the selection of the study groups; the comparability of the groups; and the ascertainment of either the exposure or outcome of interest for case–control or cohort studies respectively57. The risk of bias assessment tool includes the following domains: selection domain, including representativeness of the sample, non-respondents, and ascertainment of the exposure (risk factor); comparability domain (subjects in different outcome groups are comparable based on the study design or analysis, and confounding factors are controlled); and outcome domain, such as assessment of the outcome and statistical tests. The methodological validity and quality of the included studies were also examined. Two authors (AD and IM) assessed and scored the quality of the study using Newcastle–Ottawa Scale. The authors’ mean score was used to make the final decision. Based on their performance against each tool indicator, the included studies were categorized as high-, moderate-, or low-quality. Good quality was defined as 80% or more, moderate quality as 60% to 80%, and low quality as below 60%. The quality scores of the 28 studies ranged from 70 to 90%, with most studies (20 studies) scoring 90%. All 28 studies were considered of adequate quality for inclusion in the analyses.

Statistical analysis

Statistical analysis was conducted using the STATA 18 software. The meta-analysis data demonstrating the level of aflatoxin M1 contamination in breast milk among lactating women in Africa were presented using forest plots. A meta-analysis of the mean concentration of aflatoxin M1 was performed using a random effects model using the Der Simonian Liard method of analysis to reduce the heterogeneity of the included studies58. Subgroup analyses were performed on the basis of several parameters. Bivariate and multivariate meta-regression analyses were performed to determine and identify the sources of heterogeneity. A meta-analysis of observational studies was performed based on the recommendations of the I2 statistic given by Higgins et al. (an I2 of 75/100% and above, implying considerable heterogeneity)59. To identify potential publication bias, the researchers utilized Egger's Regression Test, trim fill analysis, and visual evaluation of a funnel plot60. Sensitivity analysis was performed using the leave-one-out meta-analysis method to identify the effect of a single study on the overall estimate and to identify outliers.

Results

Search finding and risk of bias assessment

In this meta-analysis, 134 published articles were identified from legitimate and advanced databases. Using ENDNOTE and visual inspection, 27 publications were removed from all identified studies owing to duplication. The remaining 107 studies were then retained and screened based on the title and abstract. After being vetted based on titles and abstracts, 56 were eliminated. Fifty-one articles were considered eligible, and 23 studies were excluded for reasons such as studies assessing aflatoxin M1 outside Africa, systematic reviews conducted in different regions, and studies examining cow and formula milk. Finally, the systematic review and meta-analysis included 28 published and unpublished observational studies that met the inclusion criteria (Fig. 2). A thorough review of the included studies across the eight domains yielded high-quality scores. A total of 28 articles were included in the analysis.

Figure 2
figure 2

PRISMA 2020 flow diagram for systematic reviews and meta-analysis on Aflatoxin M1 in breast milk among lactating women in Africa, 2023.

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Characteristics of included studies

We included 28 observational studies in this systematic review and meta-analysis (27 cross-sectional and one cohort study) that examined aflatoxin M1 prevalence and its concentration in breast milk in Africa. The sample size of the included studies ranged from a minimum of 5 in a study conducted in Gambia37 to a maximum of 501 in studies conducted in Ghana34. The articles included were published between 198438 and 202250. Of these, 11 studies were conducted in the western Africa region27,28,29,30,31,32,33,34,35,36,37, eight in eastern Africa 34,38,39,40,41,42, seven in northern Africa43,44,45,46,47,48,49, and two in southern Africa50,51. Eight of the studies employed the enzyme-linked immunosorbent assay (ELISA) to measure the levels of aflatoxin M1 in nursing women's breast milk2,46,50,56,61,62,63,64, while the other 20 used high-performance liquid chromatography (HPLC) to detect aflatoxin M1 levels. A total of 4016 breast milk samples were included in this systematic review and meta-analysis. The main characteristics of the studies included in this systematic review and meta-analysis (Table 1).

Table 1 Characteristics of included studies in this systematic review and meta-analysis in 2023.
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Meta-analysis of prevalence of adverse perinatal outcomes of breech deliveries

Among the 28 studies, the lowest prevalence of aflatoxin M1 in breast milk samples from lactating women was reported in Angola (none)50 to a maximum of 100% in studies in Tanzania40 and Nigeria30. The meta-analysis results are shown in (Fig. 3). The overall pooled prevalence of aflatoxin M1 in the breast milk of lactating women in Africa was 53% [95% CI 40, 65]. There was significant heterogeneity among individual studies (i2 = 98.26%).

Figure 3
figure 3

Pooled prevalence of Aflatoxin M1 in breast milk among lactating women in Africa, 2023.

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Subgroup analysis of prevalence of Aflatoxin M1 in breast milk

Based on subgroup analysis by sub-region where the studies were conducted, the highest prevalence of Aflatoxin M1 in breast milk among lactating women in Africa was observed in studies conducted in eastern African countries. The pooled prevalence in eastern Africa was 62% (95% CI 39–82). Subgroup analysis by aflatoxin M1 detection showed that the highest prevalence of aflatoxin M1 in breast milk among lactating women in Africa was observed in studies utilizing high-performance liquid chromatography (HPLC). The pooled prevalence in studies using HPLC as a method of detection was 54% (95% CI 39–69). Based on the publication year, the highest prevalence was observed in studies conducted between 2010 and 2019. The pooled prevalence of aflatoxin M1 in breast milk from lactating women in Africa from 2010 to 2019 was 68% (95% CI 47–85) (Fig. 4). When we observed heterogeneity, there was a decline in heterogeneity among the subgroups.

Figure 4
figure 4

Subgroup analysis of the pooled prevalence of Aflatoxin M1 in breast milk among lactating women in Africa based on publication year, 2023.

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Publication bias

To observe publication bias, a visual inspection of the funnel plot was carried out, which showed that there was no publication bias despite significant heterogeneity among studies (Fig. 5). Egger's test for small study effects showed no effect (P = 0.908). Furthermore, the trim fill analysis also showed no difference in the observed or combination of observed and imputed effect size estimates in the random effect model utilizing the Der Simonian Liard.

Figure 5
figure 5

Funnel plot of prevalence of adverse perinatal outcomes of breech deliveries in Ethiopia, 2023.

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Bivariate and multivariate meta-regression

The pooled prevalence of aflatoxin M1 level shows that there was heterogeneity, the I-square test statistics were significant, and a meta-regression analysis was performed (I2 = 98.26, P = 0.001). Bivariate and multivariate meta-regression analyses were performed using different variables. A meta-regression study discovered that the publication year was the source of heterogeneity. However, other study-level covariates were not statistically significant (Table 2).

Table 2 Bivariate and multi variate meta-regression analysis to check heterogeneity, 2023.
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Aflatoxin M1 concentration in breast milk

Of the 28 studies, 15 reported the mean aflatoxin M1 concentration in breast milk. Of them, the mean concentration of aflatoxin M1 is reported as in studies done in Ghana (369 ng/l), Cameroon (315 ng/l), Egypt (74.413 ng/l), Nigeria (66.2 ng/l), Nigeria (65 ng/l), Nigeria (58.2 ng/l), Sudan (22 ng/l), Egypt (21.1 ng/l), Nigeria (15 ng/l), Egypt (7.1 ng/l), Morrocco (5.75 ng/l), Nigeria (4.02 ng/l), Egypt (2.75 ng/l), and in Sierra Leone (0.8 ng/l). The pooled mean concentration of aflatoxin M1 in breast milk was 93.02 ng/l (95% CI 17.5 to 168.6).

Sensitivity analysis

A meta-analysis using the Der Simonian Liard method was performed to assess the effect of a single study on the overall estimate of the rest of the studies in the meta-analysis results and to identify outliers. As shown in (Fig. 6), when individual studies were removed and the overall prevalence was estimated, no significant deviation from the previously determined prevalence was observed. No outliers were observed.

Figure 6
figure 6

Leave one out meta-analysis of adverse perinatal outcomes in breech delivery among women in Ethiopia, 2023.

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Discussion

The goal of this systematic review and meta-analysis was to determine the prevalence of aflatoxin M1 in breast milk among lactating women in Africa. In this review, we discuss the overall pooled prevalence of aflatoxin M1 in breast milk among lactating women in Africa. Contaminants in foods that cause health problems include pathogens and toxins, which are present in raw materials or are introduced during processing. Aflatoxins are mycotoxins produced by certain fungi and are ubiquitous in soils in tropical and subtropical areas65. The maximum level of aflatoxins in foods is regulated in many countries owing to their harmful effects on health, although the allowable limits vary65,66,67. Aflatoxins, including aflatoxin B1 (AFB1) and aflatoxin M1 (AFM1), are the most potent carcinogens among all mycotoxins and are classified as Group 1, meaning that they have been proven to be carcinogenic to humans68. Aflatoxin M1 (AFM1) is a monohydroxylated metabolite of AFB1 that is secreted in milk and can be used as a biomarker of AFB1 exposure19. Human beings are exposed to these carcinogenic agents either through occupational activities, such as engaging in poultry production, or food and/or milk contaminated by aflatoxin AFB169,70,71. Moreover, a few studies have pointed out that human health risks are related to the presence of aflatoxins in food66,67,72. Grains and grain‐based products made the largest contribution to the mean chronic dietary exposure to AFB1 in all age classes, whereas liquid milk and fermented milk products were the main contributors to AFM1 exposure66,73. Aflatoxin M1 (AFM1), a human carcinogen, is found in milk products and may potentially have severe health impacts on milk consumers65.

This systematic review and meta-analysis aimed to determine the prevalence and concentration of Aflatoxin M1 (AFM1) in breast milk among lactating women in Africa. In this study, the overall pooled prevalence of AFM1 was 53% (95% CI, 40, 65; I2 = 98.26%, P = 0.001). This finding confirmed that more than half of lactating women’s breast milk was contaminated with aflatoxin M1 in Africa. This is a vivid confirmation of how these mutagenic and carcinogenic factors are widely and severely distributed in the study area, causing profound sequelae in both mothers and children. This calls all policymakers and concerned bodies, particularly agricultural experts, to hugely and profoundly emphasize mitigating risk factors that contaminate the food, such as maize, ground nuts, cocoa beans, and cassava, which act as precursors for M1, which are commonly found in breast milk with carcinogenic agents. This study was supported by a systematic review and meta-analysis conducted on a global scale in 2019, where the highest prevalence was reported in Africa74. One plausible justification for the highest prevalence of aflatoxin M1 on the continents of Africa is linked to the fact that different dietary habits and cultures of that particular community have been practiced74. Moreover, it is reasonable to assume that the highest rates of AFM1 prevalence in breast milk occur when whole-meal cereals, potatoes, bread, rice, and pasta, are the primary source of protein and energy for mothers, owing to the high cost of feeding75.

Moreover, this study revealed enormous variation in the burden of aflatoxins M1 across the continent. Accordingly, lactating women residing in the eastern region of Africa experienced the highest burden of aflatoxin M1 62%, whereas those inhabiting the southern region had the lowest level of aflatoxin M1, accounting for only 4%. One of the possible explanations for this widespread distribution of aflatoxins M1 in the eastern region of Africa could be that the country situated in this region is enormously and immensely affected by aflatoxins B1, which swept the face of the earth the region. For instance, previous studies have shown that aflatoxins are endemic to Uganda and Kenya76. Moreover, the pathogens responsible for the occurrence of aflatoxins, such as Aspergillus parasiticus and A. flavus, are predominantly found in the region, particularly in Kenya and Tanzania76,77,78. Furthermore, it is clear that different communities have their own traditional foods. Cereals like maize, millet, and sorghum are notable and well-known staple foods in the aforementioned region and are a major source of aflatoxins for the general population, especially lactating women78,79,80,81,82,83,84. Thus, this predominant presence leads to dietary exposure for the women, which ultimately acts as a precursor for aflatoxin M1 in women in the study region, particularly in the eastern region of Africa85. Furthermore, the variation across the region could be attributed to the agroecological zone, type of staple food, low socioeconomic status of the population, and seasonal variations (Fig. 7).

Figure 7
figure 7

Map on the prevalence and concentration of aflatoxin M1 in breast milk.

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This systematic review and meta-analysis explicitly reported a significant difference in the level of aflatoxin M1 among lactating mothers across years of publication. Thus, our study showed that the highest level of exposure of pregnant women to aflatoxins was 68%, which was reported in the years 2010–2019, whereas the lowest level was reported in the years 1980–1989, accounting for 31%. One of the possible explanations could be advancements and the discovery of new technology to diagnose aflatoxin M1, which ultimately played a role in screening and diagnosing aflatoxin M1 in lactating women86,87,88. Therefore, uncomplicated and less expensive methods of aflatoxin detection have made unreserved efforts to find relatively easy ways of detecting aflatoxins owing to the high burden of these problems. This is supported and reinforced by the fact that the escalation of problems, such as the high burden of aflatoxin M1 and its toxic effects, has attracted a large number of experts and researchers who actively work in the field to pay attention in order to instigate and implement long-term and feasible remedies and solutions. This invariably leads to well-established aflatoxin M1 detection over time89,90,91.

In the current systematic review and meta-analysis, the mean aflatoxin concentration in breast milk was assessed. The pooled mean concentration of aflatoxin M1 in breast milk was 93.02 ng/l (95% CI 17.5–168.6). The highest aflatoxin M1 concentration was found in a study conducted in Ghana, whereas the lowest was found in a study conducted in Sierra Leone (0.8 ng/l). This could lead to reductions in newborn growth and ultimately expose the individual to various types of cancer, especially hepatic cancer.

Strengths and limitations of the study

The strength of this study is that the publications were found in various genuine databases, websites, and institutional repositories. Another strength is that, to the best of our knowledge, this is the first systematic review methodology (SRM) on the aflatoxin M1 concentration in breast milk. However, most of the pieces came from a few regions. During the article search, only the English language was considered. Unpublished studies were included in this review, which may have influenced the overall estimate.

Conclusion

This finding confirmed that more than half of lactating women’s breast milk was contaminated with aflatoxin M1 in Africa. The pooled mean aflatoxin M1 concentration in breast milk was 93.02 ng/l. According to this study, the eastern region of Africa was profoundly affected compared with other regions of the continent. Thus, both the government and all stakeholders must instigate policies that mitigate the problems, thereby reducing aflatoxin toxicity in lactating women, fetuses, and newborns. Moreover, coordinated and collaborative actions and measures need to be taken to alleviate and reduce dietary aflatoxin exposure among lactating women.