Iodine source apportionment in the Malawian diet

The aim of this study was to characterise nutritional-I status in Malawi. Dietary-I intakes were assessed using new datasets of crop, fish, salt and water-I concentrations, while I status was assessed for 60 women living on each of calcareous and non-calcareous soils as defined by urinary iodine concentration (UIC). Iodine concentration in staple foods was low, with median concentrations of 0.01 mg kg−1 in maize grain, 0.008 mg kg−1 in roots and tubers, but 0.155 mg kg−1 in leafy vegetables. Freshwater fish is a good source of dietary-I with a median concentration of 0.51 mg kg−1. Mean Malawian dietary-Iodine intake from food, excluding salt, was just 7.8 μg d−1 compared to an adult requirement of 150 μg d−1. Despite low dietary-I intake from food, median UICs were 203 μg L−1 with only 12% defined as I deficient whilst 21% exhibited excessive I intake. Iodised salt is likely to be the main source of dietary I intake in Malawi; thus, I nutrition mainly depends on the usage and concentration of I in iodised salt. Drinking water could be a significant source of I in some areas, providing up to 108 μg d−1 based on consumption of 2 L d−1

Soil-type influences human selenium status and underlies widespread selenium deficiency risks in Malawi

Selenium (Se) is an essential human micronutrient with critical roles in immune functioning and antioxidant defence. Estimates of dietary Se intakes and status are scarce for Africa although crop surveys indicate deficiency is probably widespread in Malawi. Here we show that Se deficiency is likely endemic in Malawi based on the Se status of adults consuming food from contrasting soil types. These data are consistent with food balance sheets and composition tables revealing that >80% of the Malawi population is at risk of dietary Se inadequacy. Risk of dietary Se inadequacy is >60% in seven other countries in Southern Africa, and 22% across Africa as a whole. Given that most Malawi soils cannot supply sufficient Se to crops for adequate human nutrition, the cost and benefits of interventions to alleviate Se deficiency should be determined; for example, Se-enriched nitrogen fertilisers could be adopted as in Finland

Historical trends in iodine and selenium in soil and herbage at the Park Grass experiment, Rothamsted Research, UK

Long term trends in iodine and selenium retention in soil, and uptake by herbage, were investigated in archived samples from the Park Grass Experiment, initiated in 1856 at Rothamsted, UK. Soil (0-23 cm) and herbage samples from plots receiving various mineral fertilisers and organic manures, with and without lime, were analysed for Se and iodine (I) to assess the effect of soil amendment, annual rainfall, crop yield and changes in soil chemistry from 1876 to 2008. Comparing soil from limed and un-limed control (unfertilized) plots, TMAH-extractable Se and I concentrations both diverged, with time, with greater retention in un-limed plots; differences in concentration amounted to 92 and 1660 µg kg-1 for Se and I respectively after 105 yr. These differences were broadly consistent with estimated additions from rainfall and dry deposition. Offtake of both elements in herbage was negligible compared to soil concentrations and annual inputs (<0.003% of total soil I and <0.006% of total soil Se). A positive correlation was observed between I and Se concentrations in herbage, suggesting some common factors controlling bioavailability. A growth-dilution effect for I and Se was suggested by the positive correlation between growing season rainfall (GSR) and herbage yield together with soil-to-plant transfer factors decreasing with yield. Phosphate and sulphate fertilizers reduced I and Se herbage concentrations, both through ion competition and increased herbage yield. Results suggest that in intensive agriculture with soil pH control, the I requirement of grazing animals is not likely to be met by herbage alone

Potential for safe and efficient biofortification of maize crops with selenium in Malawi

Selenium (Se) is an essential element for humans, which is derived primarily from dietary sources. Habitual suboptimal dietary Se intake is associated with reduced Se status and adverse health outcomes including cardiovascular disorders, impaired immune functions and some cancers. The global extent of suboptimal dietary Se intake is difficult to estimate, but is likely to be widespread where food choices are narrow, for example, in subsistence agricultural contexts. This study aimed to: (1) characterise the likely contribution of maize grain to dietary Se intake in rural Malawi; (2) test the dependency of maize grain Se concentrations on soil factors; and (3) identify agronomic methods to improve Se concentration in maize grain. 88 field sites across Malawi were sampled across Malawi in 2009 and 2010 before determining maize grain, total soil and KH2PO4-extractable soil Se concentrations by inductively coupled plasma-mass spectrometry (ICP-MS). Dietary Se intakes from other food sources were estimated from the literature. The median maize grain Se concentration in Malawi was 0.019 mg Se kg-1 (range 0.005-0.533), representing a median intake of 6.7 µg Se person-1 d-1 from maize. Suboptimal (6.5) soils (Vertisols), probably because the dominant species of Se at high soil pH Se(VI) is more available to crops than Se(IV), as evidenced by the KH2PO4-extractable soil concentrations recorded. Total soil Se concentration ranged between 0.0521 and 0.6195 mg kg-1 but provided a poor index of Se availability. The results showed that KH2PO4-extractable Se concentrations >0.01 mg kg-1 and soil pH values >6.5 produced grain Se concentrations exceeding 0.15 mg Se kg-1, a value above which rural populations in Malawi would attain adequate Se intake. Field experiments in which three Se application methods (Na2SeO4 (aq), granular compound (NPK+Se) and granular calcium ammonium nitrate (CAN+Se) were applied were conducted at up to six sites in 2008/09 and 2009/10. Application of Se significantly increased grain and stover Se concentrations and the response was approximately linear for all sites and application methods in both years (R2 >0.90). The results showed that application of Se at 5 g Se ha-1 to maize would deliver adequate intakes for much of the population in Malawi. As total plant recovery of Se ranged from 3-45%, further work is required to identify and address the sources of this variation. In more detailed experiments, the fate of applied Se was investigated at two sites using the stable 74Se isotope. Recovery of applied Se was 0.65 and 1.08 g Se ha-1 at the Chitedze and Mbawa, sites respectively, representing 6.5 and 10.8% of the applied 10 g Se ha-1 by the maize crop; 0.2 g Se ha-1 of native soil Se was also absorbed, leaving 9.35 and 8.92 g Se ha-1 unaccounted. Of the total soil and applied fertiliser Se, fertiliser-derived Se (74Se-labelled) comprised 71 and 82% of plant-Se recovery at Chitedze and Mbawa, respectively. The residual effects of Se application on grain Se in maize crops grown in the subsequent cropping season were 0.3025 and 0.5858 µg kg-1 g-1 applied Se at Chitedze and Mbawa respectively. Residual Se detected as KH2PO4-extractable Se ranged from 0.0029 to 0.106 µg kg-1 g-1 applied Se between sites. Further studies are required to quantify the amount of Se immobilised in the soil pool or lost due to leaching or volatilisation. A further experiment examined how traditional processing procedures for maize grain affected Se concentration in maize flour. At Se fertilisation levels which would increase dietary Se intake to appropriate levels, there was no evidence that traditional milling produced any significant loss of Se from maize flour. Assessment of the contribution of maize to the dietary supply of other nutrients showed that calcium concentration, and hence intake from maize, were very low. Maize grain was low also in K, Cu and Zn but provided a good source of Fe, Mg, Mn and Mo. There is a need to monitor the concentrations of trace metals such as Cd, Co, Ni and Cr as these might exceed the daily allowance and pose a risk to human health

Dietary mineral supplies in Malawi: spatial and socioeconomic assessment

Background Dietary mineral deficiencies are widespread globally causing a large disease burden. However, estimates of deficiency prevalence are often only available at national scales or for small population sub-groups with limited relevance for policy makers. Methods This study combines food supply data from the Third Integrated Household Survey of Malawi with locally-generated food crop composition data to derive estimates of dietary mineral supplies and prevalence of inadequate intakes in Malawi. Results We estimate that >50 % of households in Malawi are at risk of energy, calcium (Ca), selenium (Se) and/or zinc (Zn) deficiencies due to inadequate dietary supplies, but supplies of iron (Fe), copper (Cu) and magnesium (Mg) are adequate for >80 % of households. Adequacy of iodine (I) is contingent on the use of iodised salt with 80 % of rural households living on low-pH soils had inadequate dietary Se supplies compared to 55 % on calcareous soils; concurrent inadequate supplies of Ca, Se and Zn were observed in >80 % of the poorest rural households living in areas with non-calcareous soils. Prevalence of inadequate dietary supplies was greater in rural than urban households for all nutrients except Fe. Interventions to address dietary mineral deficiencies were assessed. For example, an agronomic biofortification strategy could reduce the prevalence of inadequate dietary Se supplies from 82 to 14 % of households living in areas with low-pH soils, including from 95 to 21 % for the poorest subset of those households. If currently-used fertiliser alone were enriched with Se then the prevalence of inadequate supplies would fall from 82 to 57 % with a cost per alleviated case of dietary Se deficiency of ~ US$ 0.36 year−1. Conclusions Household surveys can provide useful insights into the prevalence and underlying causes of dietary mineral deficiencies, allowing disaggregation by spatial and socioeconomic criteria. Furthermore, impacts of potential interventions can be modelled

Potential for safe and efficient biofortification of maize crops with selenium in Malawi

Selenium (Se) is an essential element for humans, which is derived primarily from dietary sources. Habitual suboptimal dietary Se intake is associated with reduced Se status and adverse health outcomes including cardiovascular disorders, impaired immune functions and some cancers. The global extent of suboptimal dietary Se intake is difficult to estimate, but is likely to be widespread where food choices are narrow, for example, in subsistence agricultural contexts. This study aimed to: (1) characterise the likely contribution of maize grain to dietary Se intake in rural Malawi; (2) test the dependency of maize grain Se concentrations on soil factors; and (3) identify agronomic methods to improve Se concentration in maize grain. 88 field sites across Malawi were sampled across Malawi in 2009 and 2010 before determining maize grain, total soil and KH2PO4-extractable soil Se concentrations by inductively coupled plasma-mass spectrometry (ICP-MS). Dietary Se intakes from other food sources were estimated from the literature. The median maize grain Se concentration in Malawi was 0.019 mg Se kg-1 (range 0.005-0.533), representing a median intake of 6.7 µg Se person-1 d-1 from maize. Suboptimal (6.5) soils (Vertisols), probably because the dominant species of Se at high soil pH Se(VI) is more available to crops than Se(IV), as evidenced by the KH2PO4-extractable soil concentrations recorded. Total soil Se concentration ranged between 0.0521 and 0.6195 mg kg-1 but provided a poor index of Se availability. The results showed that KH2PO4-extractable Se concentrations >0.01 mg kg-1 and soil pH values >6.5 produced grain Se concentrations exceeding 0.15 mg Se kg-1, a value above which rural populations in Malawi would attain adequate Se intake. Field experiments in which three Se application methods (Na2SeO4 (aq), granular compound (NPK+Se) and granular calcium ammonium nitrate (CAN+Se) were applied were conducted at up to six sites in 2008/09 and 2009/10. Application of Se significantly increased grain and stover Se concentrations and the response was approximately linear for all sites and application methods in both years (R2 >0.90). The results showed that application of Se at 5 g Se ha-1 to maize would deliver adequate intakes for much of the population in Malawi. As total plant recovery of Se ranged from 3-45%, further work is required to identify and address the sources of this variation. In more detailed experiments, the fate of applied Se was investigated at two sites using the stable 74Se isotope. Recovery of applied Se was 0.65 and 1.08 g Se ha-1 at the Chitedze and Mbawa, sites respectively, representing 6.5 and 10.8% of the applied 10 g Se ha-1 by the maize crop; 0.2 g Se ha-1 of native soil Se was also absorbed, leaving 9.35 and 8.92 g Se ha-1 unaccounted. Of the total soil and applied fertiliser Se, fertiliser-derived Se (74Se-labelled) comprised 71 and 82% of plant-Se recovery at Chitedze and Mbawa, respectively. The residual effects of Se application on grain Se in maize crops grown in the subsequent cropping season were 0.3025 and 0.5858 µg kg-1 g-1 applied Se at Chitedze and Mbawa respectively. Residual Se detected as KH2PO4-extractable Se ranged from 0.0029 to 0.106 µg kg-1 g-1 applied Se between sites. Further studies are required to quantify the amount of Se immobilised in the soil pool or lost due to leaching or volatilisation. A further experiment examined how traditional processing procedures for maize grain affected Se concentration in maize flour. At Se fertilisation levels which would increase dietary Se intake to appropriate levels, there was no evidence that traditional milling produced any significant loss of Se from maize flour. Assessment of the contribution of maize to the dietary supply of other nutrients showed that calcium concentration, and hence intake from maize, were very low. Maize grain was low also in K, Cu and Zn but provided a good source of Fe, Mg, Mn and Mo. There is a need to monitor the concentrations of trace metals such as Cd, Co, Ni and Cr as these might exceed the daily allowance and pose a risk to human health

A descriptive analysis of HIV prevalence, HIV service uptake, and HIV-related risk behaviour among patients attending a mental health clinic in Rural Malawi

BACKGROUND: Human immunodeficiency virus (HIV) and mental illness are interlinked health problems; mental illness may pose a risk for contracting HIV and HIV-positive individuals are at higher risk of mental illness. However, in countries with high HIV prevalence, the main focus of HIV-related health programmes is usually on prevention and treatment of somatic complications of HIV, and mental illness is not given high priority. We examined HIV prevalence, uptake of HIV services, and HIV-related risk behaviour among people attending a mental health clinic in rural Malawi. METHODOLOGY: Semi-structured interviews were performed with patients capable to consent (94%), and with those accompanied by a capable caregiver who consented. HIV counselling and testing was offered to participants. FINDINGS: Among 174 participants, we collected 162 HIV test results (91%). HIV prevalence was 14.8%. Women were three times as likely to be HIV-positive compared to men. Two-thirds of participants reported having been tested for HIV prior to this study. The uptake of HIV-services among HIV-positive patients was low: 35% did not use recommended prophylactic therapy and 44% of patients not receiving antiretroviral treatment (ART) had never been assessed for ART eligibility. The reported rate of sexual activity was 61%, and 9% of sexually active participants had multiple partners. Inconsistent condom use with stable (89%) and occasional (79%) sexual partners, and absence of knowledge of the HIV status of those partners (53%, 63%) indicate high levels of sexual risk behaviour. CONCLUSIONS: HIV-prevalence among persons attending the clinic, particularly men, was lower than among the general population in a population survey. The rate of HIV testing was high, but there was low uptake of preventive measures and ART. This illustrates that HIV-positive individuals with mental illness or epilepsy constitute a vulnerable population. HIV programmes should include those with neuropsychiatric illness

Bioaccessibility of selenium after human ingestion in relation to its chemical species and compartmentalization in maize

International audienceSelenium is a micronutrient needed by all living organisms including humans, but often present in low concentration in food with possible deficiency. From another side, at higher concentrations in soils as observed in seleniferous regions of the world, and in function of its chemical species, Se can also induce (eco)toxicity. Root Se uptake was therefore studied in function of its initial form for maize (Zea mays L.), a plant widely cultivated for human and animal food over the world. Se phytotoxicity and compartmentalization were studied in different aerial plant tissues. For the first time, Se oral human bioaccessibility after ingestion was assessed for the main Se species (SeIV and SeVI) with the BARGE ex vivo test in maize seeds (consumed by humans), and in stems and leaves consumed by animals. Corn seedlings were cultivated in hydroponic conditions supplemented with 1 mg L−1 of selenium (SeIV, SeVI, Control) for 4 months. Biomass, Se concentration, and bioaccessibility were measured on harvested plants. A reduction in plant biomass was observed under Se treatments compared to control, suggesting its phytotoxicity. This plant biomass reduction was higher for selenite species than selenate, and seed was the main affected compartment compared to control. Selenium compartmentalization study showed that for selenate species, a preferential accumulation was observed in leaves, whereas selenite translocation was very limited toward maize aerial parts, except in the seeds where selenite concentrations are generally high. Selenium oral bioaccessibility after ingestion fluctuated from 49 to 89 % according to the considered plant tissue and Se species. Whatever the tissue, selenate appeared as the most human bioaccessible form. A potential Se toxicity was highlighted for people living in seleniferous regions, this risk being enhanced by the high Se bioaccessibility

Agronomic biofortification of leafy vegetables grown in an Oxisol, Alfisol and Vertisol with isotopically labelled selenium (77Se)

Selenium biofortification of crops is a proven technology for improving dietary nutrition. This study used isotopically labelled selenate (>99% enriched 77Se) to assess uptake and Se availability to two green vegetables, Brassica napus L (B. napus) and Amaranthus retroflexus L (A. retroflexus) grown in three contrasting Malawi soils: a Vertisol (calcareous), Alfisol (moderately acidic) and Oxisol (acidic). Plants were grown under glasshouse conditions (4 replicates; 6 kg soil per pot) following application of 77Se-enriched selenate at rates equivalent to 0, 10 and 20 g ha−1. Leaves were harvested at fortnightly intervals and the plants were then allowed to re-grow, to simulate cultivation practice. Leaf samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for selenium isotopes (77Se and 78Se). The isotopic data were processed to quantify the contribution to plant Se concentration from the fertilizer and the soil. Both concentration and uptake of the fertilizer 77Se declined sharply with sequential harvests due to progressive fixation of 77Se in the soil rather than exhaustion (by uptake) of the Se applied. Initially the bioavailability of fertilizer Se was three orders of magnitude greater than the soil Se but this declined to the same order of magnitude by the end of the trial. Application of 77Se had no effect on uptake of soil-derived Se. There were marked differences between the three soils studied. The relative bio-availability of the fertilizer Se followed the sequence (Vertisol > Alfisol > Oxisol) but the two crops showed the same trend in decline of fertilizer Se uptake. Thus, fixation of selenium in the soils studied was sufficiently rapid that Se biofortification of green vegetables subject to several harvests would require multiple applications during the growing season

Agronomic iodine biofortification of leafy vegetables grown in Vertisols, Oxisols and Alfisols

Iodine deficiency disorders (IDD) in sub-Saharan African countries are related to low dietary I intake and generally combatted through salt iodisation. Agronomic biofortification of food crops may be an alternative approach. This study assessed the effectiveness of I biofortification of green vegetables (Brassica napus L and Amaranthus retroflexus L.) grown in tropical soils with contrasting chemistry and fertility. Application rates of 0, 5 and 10 kg ha−1 I applied to foliage or soil were assessed. Leaves were harvested fortnightly for ~ 2 months after I application before a second crop was grown to assess the availability of residual soil I. A separate experiment was used to investigate storage of I within the plants. Iodine concentration and uptake in sequential harvests showed a sharp drop within 28 days of I application in all soil types for all I application levels and methods. This rapid decline likely reflects I fixation in the soil. Iodine biofortification increased I uptake and concentration in the vegetables to a level useful for increasing dietary I intake and could be a feasible way to reduce IDD in tropical regions. However, biofortification of green vegetables which are subject to multiple harvests requires repeated I applications