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Table 9.3 Daily intake and total body content of minerals for an adult man. Mineral Daily intake

Major minerals (mg)

Calcium

Phosphorus

Potassium

Sodium

Chloride

Magnesium

Iron

Zinc

Trace elements Fluoride

Copper

Selenium

Iodine

Manganese

Chromium

Cobalt

900 1500 3200 3400 5200 300 14.0 11.4

Total body content (g)

1000 780 140 140

95 19

2600

Source: Crown copyright is reproduced with the permission of the Controller of Her Majesty's Stationery Office (1).

Table 9.4 US recommended dietary allowances.

Infants

Children

Males

Age 06 months 612 months

1114

1518

1924

Calcium Phosphorus (mg) (mg)

400 600

800 80 1200 1200 1200

300 500

800 800 1200 1200 1200

Magnesium (mg)

40 60

120 170 270 400 350

6 10

10 10

10 10

10 10

12 15

12 15

10 15

Iodine (Mg)

40 50

90 120 150 150 150

Selenium (Mg) 10

20 20 30 40 50 70

2550 51+

Females 1114

1518 1924 2550 51+

Pregnant & lactating

1st 6 months 2nd 6 months Source: adapted with permission from NAS (3).

800 800

1200

1200 1200 800 800 1200

1200 1200

800 800

1200

1200 1200 800 800 1200

1200 1200

350 350

300 280 280 280

10 15 10 15

15 12

15 12

15 12

15 12 10 12

320 30 15

150 150

150 150 150 150 175

355 15 19 200

340 15 16 200

45 50 55 55 55 65

75 75

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Table 9.5 Estimated safe and adequate daily dietary intakes (ESADDI) for minerals.

Infants

Children & Adolescents

06 months 612 months

Adults

Source: adapted with permission from NAS (3).

Copper (mg)

  1. 40.6 0.60.7
  2. 71.0 1.01.5 1.02.0 1.52.5

Manganese (mg)

  1. 30.6 0.61.0
  2. 01.5 1.52.0 2.03.0 2.05.0

Fluoride (mg)

  1. 10.5 0.21.0
  2. 51.5 1.02.5 1.52.5 1.52.5

Chromium (Mg)

1040 2060

2080 30120 50200 50200

50200

Molybdenum (Mg)

1530 2040

2550 3075 50150 75250

75250

intake (5). Other major contributing sources were various chocolate-containing foods and drinks.

Sodium, potassium and chloride are virtually ubiquitous in the diet and so are always present in excess. Calcium is perhaps the only essential element for which cocoa powder is not a rich source; however, since cocoa is often consumed with milk in either drinks or milk chocolate, this is of little concern. Equally, however, consideration of chocolate as the dietary form of cocoa consumed may reduce some of the other mineral contributions, as the cocoa component is only a part of the formulation, albeit a significant part. Even so, both forms are capable of providing not insignificant amounts of many essential elements, although clearly chocolate should not be thought of as the sole dietary component for the attainment of mineral levels.

Requirements for magnesium are between 120 and 350 mg for most demographics. Cocoa contains almost 600 mg of magnesium per 100 g compared with 140, 165, 121 and 119 mg per 100 g for peas, white wheat, corn and rice, respectively (6). In fact, it was shown that the regular use of a cocoa product effectively prevented negative nutritional effects of a diet moderately deficient in magnesium (7). Iron present in cocoa powder is 93% usable and 85% of the phosphorus is reported to be bioavailable, although 15% of this is present as phytate (6). This tends to form complexes with both calcium and magnesium, thereby reducing their bioavailability. Cocoa or chocolate can aid in providing significant proportions of the RDA for iron, magnesium and zinc, as well as significant proportions of the ESADDI for copper and manganese.

Cocoa appears to have an affinity for minerals and its composition is reflective of its environment, being a natural product. It was feared that cocoa might also contain high amounts of heavy metals, since they are widespread in the environment (e.g. lead and cadmium in tea, yeast, crustaceans and molluscs). This was studied by Prugarova and Kovac (8), who found levels of lead and cadmium to be variable, but within acceptable levels.

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There appears to be no argument as to the high mineral content of cocoa and chocolate; however, the extent to which they are available to the body has provoked discussion and further research. In reality, there is no reason to doubt that the body efficiently utilizes most minerals present in cocoa.

Interactions and Bioavailability

The study of bioavailability of minerals is complex because of the wide range of variables that seem to affect the extent to which many of them are absorbed. This can range from macro-chemical interactions, such as oxalates with calcium and phosphorus as phytate with zinc, to micro-chemical reactions, such as ascorbic acid with iron and mineral/mineral interactions. Additionally, there are lifestyle factors such as fasting, which can influence mineral absorption.

Oxalates/Calcium

Cocoa and consequently chocolate are rich in oxalic acid. In the presence of oxalic acid or its anion oxalate, calcium easily forms water-insoluble calcium oxalate, which can form into renal calculi or kidney stones in predisposed individuals (9). Cocoa was found to contain 0.721.18% oxalic acid on a fat-free basis (6). Kasidas and Rose (10) determined the oxalate content of common foods and found high levels in rhubarb, spinach, tea, beetroot (beets), peanuts, chocolate and parsley in approximate descending concentration.

Since calcium is essential to health and has come under greater scrutiny as more is known about osteoporosis, the possible effect of oxalate interfering with the availability of calcium takes on a greater significance. Indeed, there are examples in calcium deficiency during which, if insufficient calcium is present to provide for its various non-bone functions, the body can withdraw more calcium from the bones than is being deposited, leading to potentially serious reductions in bone strength (11).

A study by Nguyen et al. (12) measured a number of physiological parameters, notably calciuria, oxaluria, phosphaturia, as well as diabetes parameters such as plasma glucose insulin, C peptide, etc., following ingestion of a single 100 g dark chocolate bar against a 55 g sucrose control. They found a striking increase in oxaluria after chocolate ingestion with no change in the sucrose control group. This was consistent with previous findings by Balcke et al. (13), who also found increased oxaluria, but found no significant differences in oxalate excretion between groups consuming 50 g or 100 g chocolate bars, suggesting a plateau level beyond which no greater oxaluria is caused. Nguyen et al. also found calciuria increased after both chocolate and sucrose ingestion (12).

The authors suggest that these urinary changes may favor the formation of calcium oxalate calculi. These findings, and the work of Lagemann et al. (9),

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