Introduction to Human Nutrition

Minerals and Trace Elements 235

Nickel

Adrenal glands (25 ng/g)Bone (33 ng/g)Kidney (10 ng/g)Thyroid (30 ng/g)

Urine as low molecular

weight complexes

Binding of Ni

2 − by various ligands including amino acids

(especially histidine and cysteine), proteins (especially albumin) and a macroglobulin called nickeloplasmin important in transport and excretion; Ni

2 + component

of urease; Ni

3 + essential for enzymic hydrogenation,

desulfurization and carboxylation reactions in mostly anaerobic microorganisms

Cofactor or structural component in specifi c

metalloenzymes; role in a metabolic pathway involving vitamin B

and folic 12

acid; role similar to potassium; neurophysiological function

Rubidium

Brain (4

μg/g)

Kidney (5

μg/g)

Liver (6.5

μg/g)

Testis (20

μg/g)

Urine; also signifi cant

amounts excreted through intestinal tract

None identifi ed

Role similar to potassium; neurophysiological

function

Silicon

Aorta (16

μg/g)

Bone (18

μg/g)

Skin (4

μg/g)

Tendon (12

μg/g)

Urine

Silicic acid (SiOH

) is the form believed to exist in 4

plasma; magnesium orthosilicate is probably the form of silicon in urine. The bound form of silicon has never been rigorously identifi ed

Structural role in some mucopolysaccharides or

collagen; role in the initiation of calcifi cation and in collagen formation

Tin

Bone (0.8

μg/g)

Kidney (0.2

μg/g)

Liver (0.4

μg/g)

Urine; also signifi cant

amounts in bile

Sn

2 + is absorbed and excreted more readily than Sn

4 +

Role in some redox reactions

Vanadium

Bone (120 ng/g)Kidney (120 ng/g)Liver (120 ng/g)Spleen (120 ng/g)Testis (200 ng/g)

Urine; also signifi cant

amounts in bile

Vanadyl (VO

2 +), vanaclate (H

VO 2

− or VO^4

−) and^3

peroxovanadyl [V-OO]; VO

2 + complexes with proteins,

especially those associated with iron (e.g. transferrin, hemoglobin)

Lower forms of life have haloperoxiclases that

require vanadium for activity; a similar role may exist in higher forms of life

Reproduced from Nielsen (1999) in Sadler

et al. Encyclopaedia of Human Nutrition

, copyright 1999 with permission of Elsevier.

None of the suggested biological functions or roles of any of the ultratrace elements has been conclusively or unequivocally id

entifi ed in higher forms of life.