Chemistry Reference
In-Depth Information
because of the lack of data showing adverse effects of silicon (Food and
Nutrition Board: Institute of Medicine, 2001).
The FNB (Food and Nutrition Board: Institute of Medicine, 2001) set
no RDA or AI for silicon. Based on the US Total Diet Study (1991-1997), the
median intake of silicon was 14 and 21 mg/d for women and men, respectively
(Food and Nutrition Board: Institute of Medicine, 2001). The range of
intakes (1st and 99th percentiles for all individuals) was 3.5-80 mg/d.
Animal studies indicate that the silicon content of connective tissue
(e.g., aorta and tendon) is four to five times richer in silicon than soft
tissues (e.g., liver, heart and muscle), which contain 2-10 mg/g dry weight
(Carlisle, 1997). The mean concentration of silicon in human milk has been
reportedtobe0.47mg/lupto5months postpartum (Anderson, 1992).
Bovine milk apparently contains a similar amount of silicon (Jugdaoh-
singh et al., 2002). Thus, dairy products contribute very little to the dietary
intake of silicon.
10.20.
Vanadium
Vanadium is not generally accepted as an essential nutrient; however, it can
be bioactive. Its ability to inhibit selectively protein tyrosine phosphatases at
submicromolar concentrations probably explains a broad range of effects
found for vanadium, most notably insulin-mimetic action. Additionally,
limited animal deprivation studies suggested that vanadium deprivation
alters thyroid hormone metabolism, impairs reproduction and induces bone
and joint abnormalities. In lower forms of life, some haloperoxidases require
vanadium. Vanadium is a relatively toxic element for humans (Nielsen, 1997;
Food and Nutrition Board: Institute of Medicine, 2001). The threshold for
toxicity through ingestion apparently is between 10 and 20 mg/d. Signs of
toxicity include abdominal pain, anorexia, nausea and diarrhea.
The FNB (Food and Nutrition Board: Institute of Medicine, 2001) set
no RDA or AI for vanadium, or an UL for infants. An UL of 1.8 mg/d was set
for adults older than 18 yr. Typical intakes of vanadium are 6-18 mg/d for
adults (Pennington and Jones, 1987).
Vanadium concentrations in tissues normally are
<
10 ng/g fresh weight
(Nielsen, 1997). Bone apparently is a major sink for excessive retained vana-
dium. Human colostrum, transitional and mature milk were found to gen-
erally contain
<
1 ng vanadium/g dry weight (Kosta et al., 1983). Bovine milk
may be a significant dietary source of vanadium because it reportedly con-
tains about 3 ng vanadium/g (Myron et al., 1977). However, a fivefold
variation in the vanadium content of milk, depending upon geographic loca-
tion, has been described (Soremark, 1967). Apparently, the vanadium in milk
