Estimation of mineral and trace element intake in vegans living in Japan by chemical analysis of duplicate diets

doi:10.4236/health.2011.311113

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Vol.3, No.11, 672-676 (2011)

doi:10.4236/health.2011.311113

Health

Estimation of mi neral and trace element int ak e in vegans

living in Japan by chemical analysis of duplicate diets

Munehiro Yoshida*, Noriko Ôgi, Yuki Iwashita

Laboratory of Food and Nutritional Sciences, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Japan;

*Corresponding Aut hor: [email protected]

Received 10 September 2011; Revised 5 October 2011; Accepted 21 October 2011.

ABSTRACT

Thirty-six daily duplicate diet samples were col-

lected from 12 healthy female Japanese vegans

and sodium, potassium, calcium, magnesium,

phosphorus, iron, zinc, copper, manganese,

iodine, selenium, chromium and molybdenum in

the diets were measured to estimate mineral

and trace element intake by Japanese vegans.

Significantly higher intake of potassium, mag-

nesium, phosphorus, iron, copper, manganese

and molybdenum was observed in vegans than

in general Japanese women, but no difference

was observed in sodium, iodine, selenium and

chromium intake. Vegan calcium intake tended

to be low compared to that of general women

but the difference was not significant. Since

high potassium, magnesium and iron intakes

cannot be achieved by general Japanese diets

and high intake of potassium and magnesium

may preven t hyperex tensio n and cardi ovascula r

disease in vegans, there are few problems with

Japanese vegan diets regarding mineral and

trace element intake, except for calcium intake,

which is low as it is in the general Japanese

people.

Keywords: Vegan; Mine ral intake; Trace Element

Intake; Duplicate Diets; Japan

1. INTRODUCTION

Vegetarian diets, essentially excluding animal foods,

have become increasingly popular in developed coun-

tries [1]. These diets are classified according to the types

of animal foods consumed, and strict vegetarians con-

suming no foods of animal origin are known as vegans.

Although vegan diets cause lower serum cholesterol,

lower blood pressure and a reduced risk of cardiovascu-

lar diseases, eliminating all animal foods from the diet

increases the risk of several micronutrient deficiencies,

including vitamin B12, vitamin D and n-3 fatty acids [2].

Regarding the intake of minerals and trace elements,

vegetarians, including vegans, show low intakes of cal-

cium, zinc and selenium because the main sources of

these micronutrients are animal foods in Western diets

[3,4].

Traditional Asian diets are predominately p lant-based,

differing from Western diets. In Japan, although the

consumption of meat and dairy products has increased

along with the Westernization of society, more than

three quarters of the energy intake still depends on plan t

foods [5]. Accordingly, it is thought that the effect of

adopting a vegan diet on the nutrient intake pattern is

different between the West and Japan. However, little

research has examined the nutrient intake of vegetarians

in Japan [6], and research on the intake of minerals and

trace elements by Japanese vegans is scarce. In the pre-

sent study, to evaluate mineral and trace element intake

by Japanese vegans, duplicate diet samples were col-

lected from Japanese vegans, and concentrations of so-

dium, potassium, calcium, magnesium, phosphorus, iron,

zinc, copper, manganese, iodine, selenium, chromium

and molybdenum were measu red.

2. SUBJECTS AND METHODS

2.1. Subjects and Duplicate Diet

Sampling

In the present study, vegans were defined as people

eating food of plant origin only. Twelve healthy female

vegans were recruited through a vegetarian food shop

located in Chiba Prefecture, Japan. The characteristics of

the subjects are described in Table 1. Duplicate meals,

beverages and between-meal snacks were collected over

24 h period; 36 duplicate diets from 12 subjects were

sampled for 3 consecutive days between September and

November 2010. All subjects gave informed consent for

the use of their personal information in this study.

M. Yoshida et al. / Health 3 (2011) 672-6 76

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Table 1. Characteristics of vegan subjects (n = 12).

Mean ± SD Median

Age (y) 48.4 ± 12.9 47.5

Duration of vegan d ie t (y) 20.7 ± 14.5 12.0

Height (cm) 156.4 ± 7.7 157.0

Weight (kg) 49.1 ± 8.9 48.5

Body mass index (kg/m2) 19.9 ± 2.4 19.7

2.2. Treatment of Samples

The daily duplicate diet sample was freeze-dried, ho-

mogenized and milled. Approximately 1 g of the dried

sample was mixed with 200 mL of 1% HCl, shaken for

30 min and centrifuged. The supernatant was filtrated

with 0.45-µm membrane filter. Filtrate thus obtained

was used for the determination of sodium and potassium.

Another 1 g of the dried sample was heated with 10 mL

metal-free HNO3 until the disappearance of insoluble

components, and then, 2 mL metal-free HClO4 was

added to the digestion mixture, which was further heated

until the appearance of white vapor of HClO4. The vol-

ume of the digest was made up to 10 mL with pure water.

Diluted digest thus ob tained was used for the determina-

tion of calcium, magnesium, phosphorus, iron, zinc,

copper, manganese, selenium and molybdenum. For the

analysis of chromium, approximately 1 g of the dried

sample was heated in an electric furnace (F-B1414M; As

One, Osaka, Japan) at 550˚C for 16 h [7]. After dry in-

cineration, the remaining ash was dissolved in 10 mL of

0.1 M HNO3. Iodine in the dried samples was extracted

with 0.5% tetramethylammonium hydroxide (TMAH)

[8]. Two hundred milligrams of the dried samples was

mixed with 40 mL of 0.5% TMAH and left overnight.

The mixture was heated at 60˚C for 6 h and centrifuged.

The supernatant was filtrated through a 0.45-µm mem-

brane filter.

2.3. Analysis

Sodium, potassium, calcium, magnesium, iron, zinc,

copper and manganese were measured using atomic ab-

sorption spectrometer (AA-6300; Shimadzu, Kyoto, Ja-

pan). Iodine, selenium, chromium and molybdenum were

determined by inductively coupled plasma mass spec-

trometry (ICPMS) with direct nebulization. The ICPMS

operating conditions were as fo llows: instrumen t, ICPM-

8500 (Shimadzu); forward power, 1200 W; coolant gas

flow rate, 7.0 L/min; auxiliary gas flow rate, 1.5 L/min;

nebulizer gas flow rate, 0.58 L/min; sampling depth, 5.0

mm; integration time, 2.0 s; number of run, 20; mode of

analysis, pulse; isotopes monitored, 52Cr, 82Se, 95Mo,

97Mo, 98Mo and 127I. Rhodium (103Rh) and tellurium

(126Te, 128Te and 130Te) were used as internal standards.

Phosphorus was determined with vanadomolybdate ab-

sorption spectrometry [9]. Protein, total lipid and energy

were analyzed by a commercial service system (Japan

Functional Food Analysis and Resear ch Center , Fukuoka,

Japan).

2.4. Statistical Analysis

For each subject, mean daily intake was calculated

from the analytical results of duplicate diet samples from

3 consecutive days. The mean and median of the daily

intake for 12 subjects were then calculated. For iodine,

the mean and median were also calculated when each

value was logarithmically transformed because values

highly varied. Mean daily intake for 12 subjects was

statistically compared with the mean daily intake by

general Japanese women aged 30 to 49 y described in

the National Health and Nutritional Survey in Japan

(NHNSJ) [10] by calculation of the Z-score; in which

women aged 30 to 49 y in NHNSJ, 2008 (n = 1053)

were regarded as a population.

3. RESULTS AND DIS CUS SION

In Table 2, daily intake of major nutrients, minerals

and trace elements by 12 Japanese female vegans was

summarized and compared with those by general Japa-

nese women and several criteria in the Dietary Reference

Intakes for Japanese (DRIJ) [11]. For the intake of en-

ergy, protein and total lipids, no difference was observed

between vegan s and general women.

Among major mineral intake, calcium intake by ve-

gans was below the estimated average requirement

(EAR) and tended to be low compared to that by the

general population. In several Western researches, cal-

cium intake by vegans was markedly lower than that by

omnivores [12] and lacto-vegetarians [13]. In the present

analysis, vegan calcium intake was somewhat low but

was not significantly lower than in the general Japanese

calcium intake. Since calcium intake by general Japa-

nese people is always low due to the low consumption of

dairy products, the low calcium intake of Japanese ve-

gans may be inconspicuous.

Phosphorus intake by vegans was markedly higher

than by general women. In Western research, a vegan

diet contains low phosphorus and is appropriate for pa-

tients with renal failure [14]. In the West, because the

major source of phosphorus in general diets is dairy

products, vegan phosphorus intake is comparatively low;

however, Japanese people ingest phosphorus mainly

from plant foods [5]. The difference in the source of

M. Yoshida et al. / Health 3 (2011) 672-6 76

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Table 2. Intake of energy, protein, lipids, minerals and trace elements in Japanese vegans.

Vegans ( n = 1 2 ) NHNSJ, 20081) DRIJ, 20102)

Mean ± SD Median Mean ± SD MedianEAR RDA AI DG UL

Energy (kcal) 1847 ± 141 1840 1682 ± 469 1645 1750 - - - -

Protein (g) 56.2 ± 8.1 58.4 60.2 ± 19.0 58.7 40 50 - - -

Lipids (% energy) 20.8 ± 7.3 21.0 24.5 ± 14.1 22.6 - - - 20 - 25-

Sodium (mg) 3649 ± 1719 3029 3696 ± 14153) 3538

3) 590 3) - - <29503) -

Potassium (mg) 3610 ± 1272* 3217 1983 ± 777 1891 - - 2000 2800 -

Calcium (mg) 361 ± 122 389 440 ± 224 406 550 650 - - 2300

Magnesium (mg) 494 ± 112* 462 214 ± 80 204 240 290 - - -

Phosphorus (mg) 1225 ± 311* 1197 8 54 ± 284 830 - - - - 3000

Iron (mg) 13.0 ± 2.4* 12.2 6.9 ± 3.0 6.5 9.0 11.0 900 - 40

Zinc (mg) 8.3 ± 1.6 9.1 7.1 ± 2.4 6.9 8 9 - - 35

Copper (mg) 1.75 ± 0.37* 1.66 1.00 ± 0.35 0.96 0.6 0.7 - - 10

Manganese (mg) 7.5 ± 2.2 7.9 - - - - 3.5 - 11

Iodine (µg) 1865 ± 1934 1158 - - 95 130 - - 2200

788 (255 - 2441)4) 7465)

Selenium (µg) 87 ± 34 76 - - 20 25 - - 230

Chromium (µg) 27 ± 8 28 - - 25 30 - - -

Molybdenum (µg) 540 ± 207 563 - - 20 25 - - 500

*Signif i can t differen ce f r o m NHNSJ da t a was obs er v ed at p < 0.001 by calculation of Z-score; 1)Values for general Japanese women aged 30 to 49 y (n = 1053)

quoted from the National Health and Nutrition Survey in Japan, 2008 [10]; 2)Criteria for Japanese women aged 30 to 49 y in Dietary Reference Intakes for

Japanese, 2010 [11]; EAR, estimated average requirement; RDA, recommended dietary allowance; AI, adequate intake; DG, tentative dietary goal for prevent-

ing lifestyle-related diseases; UL, tolerable upper intake level; 3)Calculated from the values for salt; 4)Geometrical mean with SD range in parentheses; 5)Median

calculated after logarithmic transformation of data for each daily duplicate diet sample.

phosphorus may contribute to the difference in phos-

phorus intake between Western and Japanese vegans. In

addition, phytate may contribute to the high phosphorus

intake in vegans because whole grains and beans contain

it at a high level.

No difference was observed between vegans and gen-

eral women in sodium intake. On the other hand, vegan

potassium intake was markedly higher than by general

women and far exceeded the tentative dietary goal for

preventing lifestyle-related diseases (DG) in DRIJ.

Similarly, markedly higher magnesium intake was ob-

served in vegans than in general women. This high in-

take of potassium and magnesium is probably due to the

high consumption of vegetables and fr ui t .

Among trace element intake, significantly higher iron

and copper intake was observed in vegans than in gen-

eral women. Similarly, manganese and molybdenum

intake by vegans was markedly higher than by general

Japanese, as described in several reports [15,16]. Intake

of these four trace elements far exceeded the recom-

mended dietary allowance (RDA) or the adequate intake

(AI) in DRIJ. High intake of copper and manganese is

also reported in Western researches [17], probably, be-

cause the high consumption of whole grains and beans

results in high intake of these trace elements. The mean

and median of vegan molybdenum intake exceeded the

tolerable upper intake level of this element in DRIJ. This

is also caused by high consumption of cereals and beans

since they particularly soybean, contain molybdenum at

a high level [16].

Although vegan zinc intake has been reported to be

low [12], there was no difference between vegans and

general women; however, because it has been reported

that the serum zinc level in Japanese vegetarians tends to

be low [18], it is necessary to examine whether phytate

and/or dietary fiber, which are contained in whole grains

and beans at a high level, decrease the bioavailability of

zinc in Japanese vegan diets.

Since the main sources of selenium in general Japa-

nese diets are fish, meats and eggs [19], the low sele-

M. Yoshida et al. / Health 3 (2011) 672-6 76

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nium intake by Japanese vegans is concern; however,

selenium intake by Japanese vegans was comparable to

that by general Japanese described in several previous

reports [19-21]. Japanese vegans may ingest selenium

from imported wheat and soybeans, which contain sele-

nium at a high level [22]. Similarly to selenium intake,

iodine and chromium intake by vegans was also compa-

rable to general Japanese people described in the litera-

ture [20,23].

In conclusion, Japanese vegans are estimated to ingest

high potassium, magnesium, phosphorus, iron, copper,

manganese and molybdenum compared to general Japa-

nese people. In particular, high potassium, magnesium

and iron intake cannot be achieved by ingesting general

Japanese diets. High intake of potassium and magnesium

may lead to the preventing of hyperextension and car-

diovascular disease in vegans [24]. Accordingly, there

are few problems with Japanese vegan diets regarding

mineral and trace element intake, except for calcium

intake, which is low as it is in general Japanese people.

4. ACKNOWLEDGEMENTS

This study was supported by a grant for comprehensive research on

cardiovascular and lifestyle disease from the Ministry of Health, La-

bour and Welfa re of Japan.

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