Zinc - Toxicology of Metals - page 909

that Zn administration, given other potentially limiting
micronutrients, was more effi cacious for neuropsycho-
logical functions than Zn alone or other micronutrients
alone (Sandstead et al ., 1998). In addition, a study in 221
low-income infants from rural Bangladesh found that
Zn given alone, with iron, and/or other micronutri-
ents had a benefi cial effect on orientation-engagement
behaviors (Black et al ., 2004).
Zinc is also essential for nerve conduction (Terril-
Robb et al ., 1996; Goto et al ., 2001). In 12 patients with
renal failure undergoing hemodialysis, polyneuropa-
thy and hypogeusia improved after Zn administration
(Sprenger et al ., 1983). In another study, 33 premenopau-
sal women not taking birth control pills displayed an
association between plasma Zn <10.7

children is best accomplished by assurance that other
potentially limiting micronutrient defi ciencies are absent
(Ronaghy et al ., 1974; Sandstead, 1999; Solomons et al .,
1999). Failure to control treatment experiments for other
micronutrient defi ciencies can result in no growth (Carter
et al ., 1969; Ronaghy et al ., 1969) or suboptimal growth
(Brown et al ., 2002).
Because growth is a relatively slow process, obser-
vations are usually made over long intervals of time
using standardized instruments (Gibson, 1990). Alter-
nately, increases in stature can be detected over consid-
erably shorter intervals by measurement of the lower
leg by use of a highly sensitive digitized device (Sand-
stead et al ., 1998; Cronk et al ., 1989; Stallings and Cronk
1993).
Methods that accurately detect small changes in
the components of body composition are, for tech-
nical reasons, generally not suitable for population
surveys or other fi eld studies. Such methods include
measurement of 40 K by whole-body gamma counter
to derive body cell mass, densitometry to derive body
fat, and isotope dilution measurement of body water
by use of deuterium oxide (Lukaski et al ., 1981). In
addition, dual energy X-ray absorptiometry (DEXA)
is used to measure fat mass, lean tissue mass, and
total body bone mineral (Haarbo et al ., 1991).
In contrast to other approaches, body composition
(body water, body fat, and fat-free mass) can be derived
by use of a portable instrument that measures bioelec-
trical impedance (Lukaski et al ., 1985). The method was
used to assess patients with HIV (Earthman et al ., 2000),
postsurgical patients (Meguid et al ., 1992), healthy
children (Goran et al ., 1993), children with acute and
subacute hydration disorders (Mazariegos et al ., 1998),
Mexican-American children at risk of type 2 diabetes
mellitus (Trevino et al ., 1999), and changes in fat-free
mass of Mexican-American children who participated
in a 10-week randomized placebo and micronutrient-
controlled trial of Zn or Fe with other micronutrients
(Egger et al ., 1999).

g/
L) and increased sensitivity of gustatory nerves to elec-
trical stimulation, in contrast to subjects with plasma
Zn >10.7

µ mol/L (700 µ

mol/L (Yokoi et al ., 2003).
In contrast to the preceding, administration of 53 mg
Zn daily by mouth adversely affected verbal memory
of postmenopausal women in a prospective experi-
ment (Penland et al ., 1999) (Table 3).
It is unknown how rapidly Zn defi ciency or excess
can change neuropsychological function or how rap-
idly recovery occurs.

µ

6.2.5 Dark Adaptation

Zinc and retinol are essential for dark adaptation. Reti-
nol dehydrogenase/retinaldehyde reductase requires
Zn for function (Russell et al ., 1983). The effi cacy of Zn
for nyctalopia (night blindness) was shown in patients
with Zn defi ciency and alcohol related or biliary cir-
rhosis (Morrison et al ., 1978; Herlong et al ., 1981) and
patients with sickle cell disease (Warth et al ., 1981). The
phenomenon can occur before plasma Zn is decreased
and is likely to be associated with low leukocyte Zn.

6.2.6 Taste Acuity

Zinc nutriture is one of many factors that affect the sense
of taste (Goto et al ., 2001; Russell et al ., 1983). Experimental
Zn deprivation (Henkin et al ., 1975; Ruz et al ., 1991), low
Zn status in Crohn's disease (Solomons et al ., 1977), and
gluten enteropathy (Solomons et al ., 1976) lowered taste
acuity (hypogeusia). A study of 385 older persons from
Italy, the United Kingdom, and France associated low Zn
status with hypogeusia (Stewart-Knox et al ., 2005).

6.2.8 Physical Examination

No physical sign is pathognomonic of Zn defi -
ciency. Short stature and underdevelopment are con-
sistent with long-standing Zn defi ciency (Halsted et al .,
1972; Sandstead et al ., 1967). Severe Zn defi ciency can
cause infected dermatitis of all surfaces. The distribu-
tion may be perioral-facial, perianal-peroneal-scrotal,
and periungual distribution, characteristic of acroder-
matitis (Arakawa et al ., 1976; Kay et al ., 1976; Neldner
et al ., 1978). Some patients display bilateral angular
oral fi ssures and cheilosis similar to those observed in
association with ribofl avin (Sebrell, 1979; Sebrell, 1958)
and pyridoxine defi ciencies (Mueller and Vilter, 1950).

6.2.7 Growth and Body Composition

The profound effects of severe Zn defi ciency on growth
and development prompted the discovery of human Zn
defi ciency (Halsted et al ., 1972; Prasad et al ., 1961; Prasad
et al ., 1963; Sandstead et al ., 1967; Halsted, 1977). Dem-
onstration of the effi cacy of Zn for growth-retarded