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Global magnesium supply in the food chain
Diriba B. Kumssa
A,B,C
, Edward J. M. Joy
A,B
, E. Louise Ander
B
, Michael J. Watts
B
,
Scott D. Young
A
, Andrea Rosanoff
D
, Philip J. White
E
, Sue Walker
C
, and Martin R. Broadley
A,F
A
School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, LE12 5RD, UK.
B
Centre for Environmental Geochemistry, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK.
C
Crops For the Future, The University of Nottingham Malaysia Campus, Jalan Broga, 43500 Semenyih,
Selangor Darul Ehsan, Malaysia.
D
Center for Magnesium Education & Research, LLC, 13-1255 Malama St., Pahoa, HI 96778, USA.
E
The James Hutton Institute, Invergowrie, Dundee, DD2 5DA, UK; Distinguished Scientist Fellowship Program,
King Saud University, Riyadh, Saudi Arabia.
F
Corresponding author. Email: martin.broadley@nottingham.ac.uk
Abstract. Magnesium (Mg) is an essential mineral micronutrient in humans. Risks of dietary Mg deficiency are affected by
the quantity of Mg ingested and its bioavailability, which is influenced by the consumption of other nutrients and ‘anti-
nutrients’. Here, we assess global dietary Mg supplies and risks of dietary deficiency, including the influence of other
nutrients. Food supply and food composition data were used to derive the amount of Mg available per capita at national levels.
Supplies of Mg were compared with estimated national per capita average requirement ‘cut points’. In 2011, global
weighted mean Mg supply was 613 69 mg person
–1
day
–1
compared with a weighted estimated average requirement for
Mg of 173 mg person
–1
day
–1
. This indicates a low risk of dietary Mg deficiency of 0.26% based on supply. This contrasts
with published data from national individual-level dietary surveys, which indicate greater Mg deficiency risks. However,
individuals in high-income countries are likely to under-report food consumption, which could lead to overestimation of
deficiency risks. Furthermore, estimates of deficiency risk based on supply do not account for potential inhibitors of Mg
absorption, including calcium, phytic acid and oxalate, and do not consider household food wastage.
Additional keywords: bioavailability, calcium, cereal, phytic acid, EAR.
Received 21 March 2015, accepted 10 June 2015, published online 5 October 2015
Introduction
Magnesium (Mg) is an essential mineral micronutrient in
humans, required for a variety of physiological functions. The
recommended nutrient intake for men 19–65 years old is
260 mg day
–1
(WHO and FAO 2004). A healthy adult contains
~24 g Mg, mainly in bone, muscle and soft tissues (Ebel and
Günther 1980; Elin 1987; Vormann 2003; WHO and FAO
2004). Magnesium is a cofactor in >350 enzymatic reactions,
with roles including protection from oxidative stress, and
metabolism of calcium (Ca), vitamin D and potassium (Ebel
and Günther 1980; Elin 1987; WHO and FAO 2004; Atkinson
et al.2009; Broadley et al.2012; Deng et al.2013; Das 2014;
Dibaba et al.2014; Rodríguez-Moran and Guerrero-Romero
2014). Deficiency in Mg can manifest as metabolic syndrome
(Gartside and Glueck 1995; Hata et al.2013; Rosanoff and
Plesset 2013; Cosaro et al.2014;Juet al.2014; Panhwar et al.
2014), lower bone-mineral density (Orchard et al.2014),
premenstrual syndrome (Elin 1987), and attention deficit
hyperactivity disorder (Blaszczyk and Duda-Chodak 2013).
Magnesium is obtained primarily from food sources, although
drinking and cooking water can make important contributions
depending on its hardness and the volume of water consumed
(Ong et al.2009). Median dissolved Mg concentrations of North
American spring, mineral, and groundwater from various regions
ranged from 0 to 130 mg L
–1
(Azoulay et al.2001). Magnesium
contents of some commercially available bottled waters in
Europe were, for example, 36, 110, and 128 mg L
–1
for Abbey
Well from the UK, Vichy Nouvelle from Finland, and Robacher
from Germany, respectively (Azoulay et al.2001). However,
unrefined cereals, legumes and green leafy vegetables are the
primary dietary sources of Mg (Broadley and White 2010;
Blaszczyk and Duda-Chodak 2013). The bioavailability and
absorption of ingested Mg is affected by other nutrients and
‘anti-nutrients’. For example, high concentrations of phytate in
cereal and legume seeds, and oxalate in some leafy vegetables,
can reduce Mg absorption through chelation in the gut (Brink
and Beynen 1991; Bohn et al.2004a). Addition of 1.5 mmol of
phytic acid (PA, in dodecasodium salt hydrate form) to white
bread reduced Mg absorption from 33% to 13% in human
feeding studies (Bohn et al.2004b). Similarly, Bohn et al.
(2004a) reported that Mg absorption from a meal containing
oxalate-rich spinach (Spinacia oleracea L.) was 27%, compared
Journal compilation CSIRO 2015 www.publish.csiro.au/journals/cp
CSIRO PUBLISHING
Crop & Pasture Science
http://dx.doi.org/10.1071/CP15096
with 37% from a meal containing kale (Brassica oleracea L.),
which has a lower oxalate concentration. Fractional Mg
absorption of 44% (Sabatier et al.2003) and 35% (Marshall
et al.1976) has been reported in typical Western diets. A study on
rats showed that increased Ca intake led to reduced intestinal
absorption and renal re-absorption of Mg (Bertinato et al.
2014), although Palacios et al.(2013) reported no effects of
Ca intake on urinary Mg excretion in females aged 11–15 years.
Nonetheless, absorption of Mg is under homeostatic control and
can increase when there is deficiency of Mg in the human body
(Hansen et al.2014).
Dietary Mg intake and the prevalence of deficiency risks can
be estimated from tissue biomarkers, food recall or food balance
sheets (FBSs) (Ford and Mokdad 2003; Broadley et al.2012;
Joy et al.2013,2014;Juet al.2014; Rodríguez-Moran and
Guerrero-Romero 2014; Kumssa et al.2015). However, the
accuracy of estimates of the prevalence of Mg deficiency risks,
using tissue biomarkers, suffers from the lack of a reliable index
(Reinhart 1988; Hansen et al.2014; Ong et al.2014). Estimates
based on dietary intakes are preferred, particularly for wide-scale
assessment. Dietary recall studies suggest high risks of Mg
deficiency. For example, ~60% of the USA population were
reported to consume Mg below an estimated average requirement
(EAR) of 330 mg person
–1
day
–1
for men aged 19–30 based on the
National Health and Nutrition Examination Survey (NHANES)
24-h dietary recall in 1999 and 2000 (Ford and Mokdad 2003).
The EAR is the daily nutrient intake estimated to meet the
requirements of half of the healthy individuals in a given age-
and sex-specific population (IOM 2000). During the 2001–02
NHANES, 64% and 67% of men and women 19 years of age,
respectively, had Mg intake less than the EAR (Moshfegh et al.
2005, cited in Rosanoff 2010). Similarly, in the UK, the National
Diet and Nutrition Survey (NDNS) from 2008–09 to 2011–12
reported that 53% of females aged 11–18 years, 14% of adults
aged 19–64 years and 19% of males 65 years had dietary Mg
intakes below their lower reference nutrient intake (LRNI), as
measured using a 4-day diary dietary record (Bates et al.2014).
The LRNI is an intake level sufficient for <2.5% of the age- and
sex-specific population group and is 190 mg person
–1
day
–1
for
all people aged 15–18 years and adult males. However,
dietary-recall or diary methods are known to be affected
by misreporting, especially under-reporting in developed
countries, and behavioural change (Bingham et al.1994; IOM
2000; Rennie et al.2004,2005,2007; Mirmiran et al.2006;
Liberato et al.2009; Archer et al.2013; Bates et al.2014;
Winkler 2014). In addition, dietary survey data are lacking in
many developing countries (Gibson 2005), as well as site-
specific and relevant food composition data to determine the
Mg concentrations of foods consumed (Joy et al.2014,2015;
Kumssa et al.2015).
Global-scale estimates of Mg supply and deficiency risks
have not been reported. However, estimates of mean global
Ca supply in 2011 of 684 211 mg person
–1
day
–1
by Kumssa
et al.(2015) based on FBSs were similar to those of Imamura
et al.(2015), who estimated median Ca intakes of 611 mg
person
–1
day
–1
(third quintile range 553–658) from a large
meta-analysis of milk consumption as a proxy for Ca intake,
based primarily on dietary recall data. The global risk of zinc (Zn)
deficiency has been estimated, based on FBS supply, to be 16%
in 2011 by Kumssa et al.(2015) and 17% in 2003–07 by Wessells
and Brown (2012). In Africa, a mean continental Mg supply of
678 mg person
–1
day
–1
was estimated from FBSs and African
food composition data, with a 0.7% prevalence of deficiency
risk (Joy et al.2014). The aims of the present study were (i)to
estimate the global risk of dietary Mg deficiency based on food
supply, composition and demographics; and (ii) to assess the
potential impact of the supply of other components of human
diet that might affect the bioavailability of Mg.
Materials and methods
Methods are identical to those described previously for
estimating the risks of dietary Ca and Zn deficiencies (Kumssa
et al.2015). Briefly, secondary data for food supply, food
composition, demography and EAR for Mg were integrated
for 145 countries with populations >1 million by using food-
supply and demographic data from 1992 to 2011. The EAR ‘cut-
point’(EAR-CP) method was used to assess the prevalence of
Mg deficiency risks.
Data sources
The four types of datasets required for this study were food
supply, food composition, the EAR for Mg, and national
demographic data. Per capita food supply data for 94 food
items were obtained from the Food and Agriculture
Organisation of the United Nations (FAO) Statistics Division
(FAOSTAT) website for the years 1992–2011 (FAO 2014).
Food composition data were obtained from the United States
Department of Agriculture (USDA) National Nutrient Database
for Standard Reference 26 (USDA SR26), which was released in
2013 (USDA 2013). The EARs for Mg were obtained from
the World Health Organisation (WHO) and FAO vitamin and
mineral requirements (WHO and FAO 2004). Demographic
data were obtained from the United Nations Department of
Economic and Social Affairs Population Division, Population
Estimates and Projection (United Nations 2013). Spatial
aggregation of countries was made based on FAO regional and
continental classification (http://faostat.fao.org/site/371/default.
aspx). Income level aggregation was obtained from the World
Data Bank, World Development Indicators in February 2015,
and countries are kept within the same group from 1992–2011
(http://databank.worldbank.org/data/reports.aspx?source=World-
Development-Indicators).
Magnesium supply
The 94 food items from the FAOSTAT food supply
(g person
–1
day
–1
) data (see Supplementary Materials table S1,
available on the Journal’s website) were matched (sensu
Stadlmayr et al.2011) with the Mg composition of fresh and/
or uncooked food commodities in the nutrient composition data.
The nutrient composition of food items was assumed not to
change with time or location. Per capita Mg supply from each
food item in each country was calculated by multiplying the
per capita food supply by its nutrient concentration. Magnesium
supply from each food commodity was summed within country
to obtain the per capita nutrient supply at a national level.
Magnesium supplies from fortification and supplements, and
drinking and cooking water were not accounted for in this study.
BCrop & Pasture Science D. B. Kumssa et al.
Magnesium intakes and requirements
Magnesium intakes were estimated as the mean per capita Mg
supply at a national level, with an inter-individual coefficient of
variation of 25% (Wessells and Brown 2012; Joy et al.2013).
The EAR for Mg is available according to age (~5-year
groupings) and gender classes (WHO and FAO 2004). As a
result, a national weighted EAR was calculated (WtdEAR)
(Eqn 1), using the population size in each age and gender
group for each country and year. For a given age or gender
group, the EAR was assumed to remain unchanged whereas the
WtdEAR varied with the population structure, which in turn
varied between countries and years. The WtdEAR for Mg is
hence assumed to approximate the per capita intake that fulfils
the Mg requirements of half of the healthy individuals in a
population of a given country in a specific year:
WtdEAR ¼SEARgroup GroupPopðÞ
TotalPop ð1Þ
where EARgroup is the EAR for Mg of a given age or gender
group, GroupPop is the population size of a given age or gender
group, and TotalPop is the total population in a given year for a
given country.
Estimated average requirement ‘cut-point’
The prevalence of Mg-deficiency risk was assessed using the
EAR-CP as described and used by Carriquiry (1999), Wuehler
et al.(2005), Joy et al.(2014) and Kumssa et al.(2015). The EAR-
CP method yields an estimate of the number of people in a given
country and year with intakes of Mg below the WtdEAR, which
is termed hereafter as the ‘deficiency risk’. The EAR-CP method
has been applied with the following underlying assumptions:
(i) little correlation between requirement and intake; (ii) the
distribution of requirement is symmetrical around the EAR;
and (iii) variability in intake is greater than the variability in
requirement (IOM 2000).
Nutritional ratio
Dietary Ca and phytate, which represents the mixed salts of PA,
or myo-inositol hexakisphosphate, were calculated in a similar
manner to Mg. The PA and Ca data are those presented previously
(Kumssa et al.2015). The Ca : Mg ratio was calculated on a
gravimetric basis (Rosanoff 2010), whereas the Mg : PA ratio
was derived from the molar weights (Mg = 24.3 g mol
–1
,PA=
660 g mol
–1
) (Cheryan et al.1983).
Aggregating information
Spatial aggregation (i.e. regional, continental, global) and
income level aggregations (i.e. low income, lower middle
income, upper middle income, high income) of the mean and
standard deviation (s.d.) of Mg supply, WtdEAR, and deficiency
risk, and Ca : Mg and Mg : PA ratios, were weighted by
the national population size. (See example in Eqns 2 and 3
below.) Aggregated information is presented as mean s.d.
unless specified.
Data analyses and visualisation
Datasets were compiled using Microsoft Excel 2013 and exported
to Microsoft Access 2013 (Microsoft Corp., Redmond, WA,
USA) to make a relational database. The database was queried
to extract the per capita Mg supply, and the WtdEAR for Mg.
The risk of Mg deficiency during the 20-year period was then
calculated in Microsoft Excel. Visualisations and calculations
of descriptive statistics were carried out in Tableau Software
for desktop version 8.3 (Tableau Software, Seattle, WA, USA),
GraphPad Prism 6 (GraphPad Software, San Diego, CA, USA)
and ArcGIS 10.2.1 (Esri, Redlands, CA, USA). Country
boundaries for thematic mapping were obtained from the
GADM Global Administrative Areas database (http://gadm.
org/, Version 2; accessed January 2014).
Aggregation of (i) per capita mean (Eqn 2) and (ii) standard
deviation (Eqn 3) of supply (mg person
–1
day
–1
), WtdEAR
(mg person
–1
day
–1
), and deficiency risk (%) of Mg at regional
level are presented as an example:
WtdMeanMgSupi¼SðMgSupjPCountryjÞ
SiPopulation ð2aÞ
where WtdMeanMgSup
i
is the weighted mean Mg supply in
region i, MgSup
j
is the Mg supply in country j, and PCountry
j
is
the population in country j.
WtdMgWtdMeanEARi¼SðMgWtdEARjPCountryjÞ
SiPopulation ð2bÞ
where WtdMgWtdMeanEAR
i
is the weighted mean MgWtdEAR
in region iand MgWtdEAR
j
is the per capita Mg WtdEAR in
country j.
WtdMgMeanDefRiski¼SðMgDefRiskjPCountryjÞ
SiPopulation ð2cÞ
where WtdMgMeanDefRisk
i
is the weighted Mg deficiency risk
(%) in region i, and MgDefRisk
j
is the Mg deficiency risk (%) in
country j.
SDiMgSupPerFood ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Si
jMgPerFoodjWtdMeanMgPerFoodi
2PCountryj
SiPopulation
s
ð3aÞ
where SD
i
MgSupPerFood
is the standard deviation of Mg supply
per food item in region i, MgPerFood
j
is the Mg composition of
a food item in country j in region i, WtdMeanMgPerFood
i
is
the weighted mean of Mg composition of a food item in region
i, PCountry
j
is the population of country j in region i, and
S
i
Population is the sum of population in region i.
SDiMgSup ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Si
jMgSupjWtdMeanMgSupi
2PCountryj
SiPopulation
s
ð3bÞ
where SD
i
MgSup
is the standard deviation of Mg supply in region i.
Global Mg supply in the food chain Crop & Pasture Science C
SDiMgWtdEAR ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Si
jMgWtdEARjWtdMgWtdMeanEARi
2PCountryj
SiPopulation
s
ð3cÞ
where SD
i
MgWtdEAR
is the standard deviation of Mg WtdEAR
in region i.
SDiMgDefRisk ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Si
jMgDefRiskjWtdMgMeanDefRiski
2PCountryj
Sri Population
s
ð3dÞ
where SD
i
MgDefRisk
is the standard deviation of Mg deficiency
risk in region i.
Results
Magnesium supply and deficiency risk
Globally, the weighted mean Mg supplies were 558 61
person
–1
day
–1
in 1992 and 613 69 mg person
–1
day
–1
in
2011, and the respective weighted mean WtdEARs were
166 3 and 173 3 mg person
–1
day
–1
. Consequently, 0.37%
and 0.26% of the population were likely at risk of dietary Mg
deficiency in 1992 and 2011, respectively. Globally in 2011, the
number of people likely to be at risk of Mg deficiency was
~14 million based on supply data (Fig. 1and Supplementary
table S2).
At a continental level in 2011, the supplies of Mg in Africa,
the Americas, Asia, Europe and Oceania, respectively, were
653 95, 556 45, 615 69, 627 54 and 552 4mg
person
–1
day
–1
; the WtdEARs for Mg were 159 3, 174 3,
174 3, 180 1 and 178 1 mg person
–1
day
–1
; and the risks
of Mg deficiency were 0.19%, 0.33%, 0.26%, 0.24% and 0.33%
(Supplementary table S3). In Africa, the Americas, Asia, Europe
and Oceania, respectively, the number of people at risk of Mg
deficiency in 2011 was 1.2, 2.8, 8.6, 1.6 and 0.1 million
(Supplementary table S3). Regionally in 2011, Mg supplies
ranged from 492 34 person
–1
day
–1
for Southeast Asia to
848 114 mg person
–1
day
–1
for Northern Africa. The risk of
Mg deficiency in 2011 ranged from 0.08% in Northern Africa to
0.64% in Caribbean (Fig. 2and Supplementary table S4). At a
country level, the supply of Mg in 2011 ranged from 340 to
944 mg person
–1
day
–1
(Fig. 3and Supplementary table S5). In
1992, the supplies of Mg ranged from 460 93 mg
person
–1
day
–1
in low-income countries to 594 57 mg
person
–1
day
–1
in high-income countries, with respective
deficiency risks of 0.75% and 0.27%. In 2011, the supplies of
Mg ranged from 549 103 mg person
–1
day
–1
in low-income
countries to 679 107 mg person
–1
day
–1
in upper middle-
income countries, with respective Mg deficiency risks of
0.35% and 0.21% (Fig. 4and Supplementary table S6).
Sources of dietary magnesium
Typically, 40–80% of dietary Mg in all regions and years
originated from cereals (Fig. 5). For example, in 2011, 79% of
dietary Mg in Afghanistan originated from wheat, 64% in
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
700
Mean Mg supply Mean Mg WtdEAR Mean Mg deficiency risk
M
g
deficienc
y
risk (%)
600
500
400
0.6
0.5
0.4
0.3
0.2
0.1
0
Mg supply & WtdEAR (mg capita–1 day–1)
300
200
100
0
Reference year
Fig. 1. Global weighted mean magnesium (Mg) supply, weighted estimated average requirement (WtdEAR) and deficiency risk
between 1992 and 2011. Capped lines are standard deviation.
DCrop & Pasture Science D. B. Kumssa et al.
Africa
800
600
400
200
0
1.5
1.0
0.5
0
1995
2000
2005
2010
1995
2000
2005
Year Year Year Year Year
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
Americas Asia Europe Oceania
Mg supply (mg capita–1 day–1)Mg deficiency risk (%)
Fig. 2. Regional population-weighted mean magnesium (Mg) supply and deficiency risk between 1992 and 2011. Horizontal broken lines represent the
population-weighted mean weighted estimated average requirement.
(a)
(b)
(c)
(d)
Mg supply (mg capita–1 day–1) Mg supply (mg capita–1 day–1)
293–450
<0.5 1.5–3.2
0.5–1.5 No data
339–450 550–650
450–550 650–944
No data
450–550
550–650 No data
650–1019
Mg deficiency risk (%)
<0.5 1.5–1.54
0.5–1.5 No data
Mg deficiency risk (%)
Fig. 3. National magnesium (Mg) supplies in (a) 1992 and (c) 2011, and Mg deficiency risks in (b) 1992 and (d) 2011.
Global Mg supply in the food chain Crop & Pasture Science E
Bangladesh from rice, and 63% in Zambia from maize
(Supplementary table S7). In high-income countries, wheat
provided 43% of dietary Mg, while aquatic plants, nuts,
potatoes and vegetables contributed 6% each to dietary Mg
(Fig. 6).
Nutritional ratios
Globally, the Ca : Mg supply ratios were 0.96 0.49 in 1992
and 1.11 0.38 in 2011 (Supplementary table S2). In 2011 at a
continental level, the Ca : Mg ratios were 0.72 0.24 in Africa,
1.55 0.41 in the Americas, 1.01 0.23 in Asia, 1.57 0.21 in
Europe and 1.69 0.08 in Oceania (Supplementary table S3).
In 2011, regionally, the Ca : Mg ratios ranged from 0.61 0.1
in Western Africa to 2.00 0.08 in Northern America
(Supplementary table S4), and at a country level from 0.36 to
2.15 (Fig. 7and Supplementary table S5). For low and high
income countries, respectively, Ca : Mg ratios ranged from
0.64 0.20 to 1.72 0.55 in 1992 and from 0.71 0.23 to
1.64 0.32 in 2011 (Fig. 4and Supplementary table S6).
Global Mg : PA ratios were 8.00 1.53 in 1992 and
7.99 1.48 in 2011 (Supplementary table S2). At a continental
level, the Mg : PA ratios in 2011 were 6.81 1.26 in Africa,
7.97 1.59 in the Americas, 8.00 1.33 in Asia, 9.49 0.94 in
Europe and 8.91 0.68 in Oceania (Supplementary table S3).
Regionally, the Mg : PA ratios in 2011 ranged from 5.65 0.49 in
Central America to 11.18 0.65 in Central Asia (Supplementary
table S4). At a country level, the Mg : PA ratios ranged from 4.67
to13.49in2011(Fig.7and Supplementary table S5). For low
and high income countries, respectively, the Mg:PA ratios
ranged from 6.02 0.8 to 9.49 1.03 in 1992 and from
6.11 0.96 to 9.21 0.87 in 2011 (Fig. 4and Supplementary
table S6).
Discussion
The global prevalence of dietary Mg-deficiency risk, based on
food supply data, was <1% during 1992–2011 and decreased
over this period. In 2011, 14 million people globally were likely
at risk of dietary Mg deficiency, based on these data. The
decreasing trend in the risk of dietary Mg deficiency is likely
due to the overall increase in global food production, especially
cereals, which are the major sources of dietary Mg (Welch and
Graham 1999; Pingali 2012; FAO, IFAD, WFP 2014). This is in
agreement with published estimates of dietary Mg-deficiency
risks for Africa (Broadley et al.2012; Joy et al.2013,2014).
The risk of dietary Mg deficiency is greater in low-income
countries.
Estimates of the risk of dietary Mg deficiency based on dietary
recalls are much greater than the above estimates (14–53%,
UK NDNS data, Bates et al.2014;64–67%, NHANES data,
Moshfegh et al. 2005, cited in Rosanoff 2010). Those reports
contrast markedly with the results presented here, which suggest
that the risks of dietary Mg deficiency for USA and UK in 2011
were 0.32% and 0.25%, respectively. This discrepancy might be
attributed in part to misreporting of dietary intakes by respondents
participating in dietary-recall surveys (Bingham et al.1994; IOM
2000; Rennie et al.2004,2005,2007; Mirmiran et al.2006;
Liberato et al.2009; Archer et al.2013; Bates et al.2014; Winkler
2014). For example, energy intake was under-reported from 24-h
dietary recall by 15% in Brazil (Avelino et al.2014), >25% in the
UK (Rennie et al.2007), and 67% for men and 59% for women in
the USA (Archer et al.2013). Galan et al.(2002) reported dietary
Mg intake in France for adult female (35–60 years) and male
(45–60 years) tapwater drinkers of 284 and 377 mg day
–1
,
respectively, using 24-h recall surveys. Charlton et al.(2005)
reported dietary Mg intakes in Cape Town, South Africa, of 228,
700
Low income High income
Lower middle income Upper middle income
(a)(c)
(b)(d)
600
500
400
300
200
100
0
Mg supply (mg capita–1 day–1)
Mg deficiency risk (%)
Ca : Mg ratioMg : PA ratio
0.8
0.6
0.4
0.2
1994 1996 1998 2000 2002 2004 2006 2008 2010
Year Year
1994
0
2
4
4
3
2
1
0
6
8
10
1996 1998 2000 2002 2004 2006 2008 2010
0
Fig. 4. Population-weighted mean (a) magnesium (Mg) supply (broken horizontal line represents weighted estimated
average requirement); (b)deficiency risk; (c) calcium (Ca) : Mg ratio (broken horizontal line is optimum Ca : Mg ratio); and
(d) Mg : phytic acid (PA) ratio between 1992 and 2011 according to income.
FCrop & Pasture Science D. B. Kumssa et al.
60
80
Eastern Africa(a)
(b)
(c)
(d)
Middle Africa Northern Africa Southern Africa Western Africa
Caribbean
Central Asia Eastern Asia
Eastern Europe
South-Eastern Asia Southern Asia
Southern Europe
Western Asia
Western Europe Australia and New Zealand
Central America Northern America
Northern Europe
Southern America
40
20
Dietary Mg contribution (%)Dietary Mg contribution (%)Dietar y Mg contribution (%)Dietary Mg contribution (%)
0
Year Year Year Year Year
Year Year Year Year
60
80
40
20
0
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
Year Year Year Year Year
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
Year Year Year Year Year
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
1995
2000
2005
2010
60
80
40
20
0
60
80
40
20
0
Fig. 5. Regional temporal trends in the percentage contribution of food groups to magnesium (Mg) supplies between 1992 and 2011 Data are shown for
(a) Africa, (b) the Americas, (c) Asia, (d) Europe and Oceania.
Global Mg supply in the food chain Crop & Pasture Science G
261, and 285 mg person
–1
day
–1
for mixed ancestry, black and
white ethnic groups, respectively, using 24-h recall surveys of
men and women aged 20–65 years. These reported Mg intakes
are less than half of our estimates of 600 and 637 mg
person
–1
day
–1
of Mg supply in 2011 for France and South
Africa, respectively. By contrast, Ca supply calculated from
FBS (Kumssa et al.2015) was only 15% greater than that
estimated from dietary-recall data using milk as a proxy
(Imamura et al.2015).
Other caveats in this study include the lack of spatial and
temporal resolution in food composition data. Thus, Mg
concentration data for foods were sourced from the USDA-
SR26 food composition database, which is centred on foods
grown in North America (USDA 2013). Thus, the impact of
different crop varieties, soil types and agronomy (White and
Broadley 2009) between and within countries and over time
cannot be accounted for in the present study (White and
Broadley 2005;Davis2009). Therefore, the estimated risks of
dietary Mg deficiency will be compromised by the absence of
relevant, reliable and up-to-date food composition data, which
require more detailed local study. For example, in a recent analysis
of dietary duplicates in Malawi from a single day (Hurst et al.
2013), mean and median Mg intakes were 418 and 353 mg
person
–1
day
–1
(n= 114). This is in broad agreement with the
low estimated risk of Mg deficiency based on FBS supply data,
but is still lower than the Mg supply estimate of 530 mg
person
–1
day
–1
in the present study. However, large differences
were observed in Mg intake from those living in Zombwe
Extension Planning Area (predominantly non-calcareous soil;
n= 56) and Mikalango Extension Planning Area (predominantly
calcareous soil; n= 58). Median Mg intake in Zombwe was
267 mg person
–1
day
–1
, compared with 538 mg person
–1
day
–1
in Mikalango (unpublished data collected during the study of
Hurst et al.2013). These differences were due primarily to
differences in cereal Mg concentrations between soil types
(Broadley et al.2012;Joyet al.2015) and to dietary choices.
For example, sorghum grain had a higher Mg concentration than
maize grain and it was consumed more often in Mikalango.
Other methodological weaknesses in determining Mg
deficiency risks from food-supply data include effects of food
processing and food waste at the household level. In terms of
food processing, the USDA food composition table (USDA
2013) shows that enriched white bread-wheat flour (25 mg
100 g
–1
) contains much less Mg than whole-grain wheat flour
(137 mg 100 g
–1
). Thus, if food processing is not captured
accurately by FBS data, then further discrepancies in
estimates of Mg deficiency risks could arise from supply-
based methods v. dietary recall. Food balance sheets also
do not capture waste at the household level and will therefore
overestimate consumption (FAO 2001). In developed
countries, household food wastage occurs from unplanned
purchases, behaviour and ‘best-before-dates’(Parfitt et al.
Aquatic Plants
Nuts
Potatoes
Vegetables
Wheat
Others
Cassava
Cereals, Other
Maize
Millet
Plantains
Pulses, Other
Rice
Sorghum
Wheat
Yams
Others
Cassava
Maize
Rice
Sorghum
Wheat
Yams
Others
Maize
Millet
Rice
Rye
Sorghum
Vegetables
Wheat
Others
13%
6%
(a)(b)
(c)(d)
6%
7%
18%
8%
5%
6%
19%
10%
29%
9%
6%
20%
12%
8%
39%
12%
7%
9%
6%
7%
5% 43%
6% 6%
6%
6%
33%
16%
15%
2%
Fig. 6. Percentage contribution of food items to total dietary magnesium (Mg) supplies in (a) low-income, (b) lower middle-income,
(c) upper middle-income, and (d) high-income countries. Others represents all food commodities that individually contribute <5% to total
dietary Mg in 2011.
HCrop & Pasture Science D. B. Kumssa et al.
2010;Erikssonet al.2012). Gustavsson et al.(2011) estimated
food waste in Europe and North America was 95–115 kg
person
–1
year
–1
,comparedwith6–11 kg person
–1
year
–1
in sub-
Saharan Africa, and South and Southeast Asia. Forcereals, 2–25%
of the initial production is wasted at household level (Gustavsson
et al.2011). Given that cereals are the major source of dietary
Mg (Fig. 6), quantifying deficiency based on FBSs is likely
to systemically underestimate Mg deficiency risk. Drinking and
cooking water can also have an important contribution to Mg
nutrition, where water Mg concentrations are sufficiently elevated
(Marier 1982;Rosanoff2013;Kanadhiaet al.2014), but this
was not assessed in this study.
The risk of Mg deficiency is determined not only by Mg
intake but also by the proportion of other nutrients and anti-
nutrients (e.g. Ca, PA, oxalate, fibre, saturated fat, etc.) in the gut
that affect its bioavailability (Vitale et al.1957; Seeling 1964;
Reinhold et al.1976; Cheryan et al.1983; Pallauf et al.1998;
Coudray et al.2003; Bohn et al.2004b). The dietary Ca : Mg
ratios based on dietary recall were 2.9 in France (Galan et al.
2002) and 1.9 in South Africa (Charlton et al.2005), compared
with our estimates of 1.69 and 0.65, respectively, in 2011. Dai
et al.(2007) reported that a Ca : Mg ratio >2.8 may affect Mg
absorption. In our study, the Ca : Mg ratio from food supply
was generally <2; however, processing of cereals is likely to
result in larger reductions in intake of Mg than of Ca, thereby
increasing Ca : Mg ratios at the intake level. For example, the
concentration of Mg in whole grain wheat was reduced by 82%,
whereas Ca was reduced by 56% when processed into un-
enriched bread flour (USDA 2013). Thus, in countries where
Ca : Mg supply ratio approaches or exceeds ~2, the impact of
Ca and other nutrients on Mg bioavailability needs to be
investigated further. Interestingly, Seeling (2006) has argued
that the rise in recommended Ca intake could affect Mg
absorption if there is not a concurrent increase in Mg. High
concentrations of PA in cereals and legumes, and oxalates in
some green leafy vegetables, can also reduce Mg absorption in
the gut because of chelation (Brink and Beynen 1991; Bohn
et al.2004a). In high-income countries, aquatic plants provided
6% of the total dietary Mg (Fig. 6), indicating the important
potential role of underutilised crops in human dietary Mg
nutrition. The estimated Mg : PA molar ratio in all countries
was 5–14, which is in the range observed to affect the
absorption of Mg (Cheryan et al.1983). At a global scale, our
results indicate that while Mg supply from agricultural
production is likely to be sufficient to meet the requirements of
the population, the prevalence of high Mg : PA ratios in diets
around the world requires further study to determine the extent
to which Mg absorption might be impaired.
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