Chemistry Reference
In-Depth Information
however, no reports in the literature about vitamin D intoxication with foods
that are consumed traditionally (Chesney, 1989). All reports of vitamin D
intoxication involve either highly fortified foods (Jacobus et al., 1992) or
pharmacological doses of vitamin D supplements (for review, see Vieth,
1999). In almost every instance of vitamin D intoxication, serum 25(OH)D
levels were
>
200 nmol/l (Jacobus et al., 1992;Vieth,1999;Zittermann,2003),
but were usually well above this level (Vieth, 1999). Vitamin D intoxication is
characterized by hypercalcaemia and hypercalciuria and can lead to the calci-
fication of soft tissues (Vieth, 1990), with minimal or no change in 1,25(OH)
2
D
3
levels (Hughes et al., 1976). In vitamin D intoxication, a serum 25(OH)D level
of
1000 nmol/l is not uncommon (Heaney et al., 1997; Vieth, 1999). In one
study, a serum 25(OH)D level of 3700 nmol/l was reported in a subject
exhibiting vitamin D intoxication after the consumption of table sugar to
which pure crystalline vitamin D
3
had been added either accidentally or
intentionally (Vieth et al., 2002). The subject in question reported extreme
pain, nausea, dehydration and severe nephrocalcinosis.
The supplemental dose of vitamin D that may lead to toxicity is unclear.
One study showed that 30 mg of vitamin D per day was sufficient to cause
hypercalciuria in one subject (Adams and Lee, 1997), yet the same vitamin D
intake was associated with vitamin D deficiency in two other studies (Chapuy
et al., 1997; Trang et al., 1998). It has been suggested that the differences
between the outcomes of these studies can be explained by sunlight exposure
(Vieth, 1999). In addition, in nearly all cases of vitamin D intoxicity except for
the study by Adams and Lee (1997), the reported vitamin D intake was above
100 mg/day (Vieth, 1999). The current No Observed Adverse Effect Level
(NOAEL) for vitamin D is set at 100 mg/day (Scientific Committee on Food,
2002). This figure is based on the consensus that at a vitamin D intake of
100 mg/day, the risk of hypercalcaemia/hypercalciuria starts to increase (Tjel-
lesen et al., 1986; Vieth et al., 2001). The upper limit (UL) for vitamin D
stands at 50 mg/day (Food and Nutrition Board, 1998; Scientific Committee
on Food, 2002), which incorporates a safety factor of 2 from the NOAEL.
12.4.
Vitamin E
12.4.1.
Chemistry and Analysis
Tocochromanols are a group of four tocopherols (
-,
-,
- and
-) and
four tocotrienols (
-,
-,
- and
-) produced at various levels and in different
combinations by all plant tissues and some cyanobacteria. All tocochroma-
nols are amphipathic molecules, with the general structures shown in
Figure 12.3. The polar head group is derived from aromatic amino acid
