Chemistry Reference
In-Depth Information
The stability of vitamin E in foods is affected by environmental
factors and food-related factors such as water activity, the degree of
unsaturation of biomembranes and the presence of trace elements such as
copper and iron (Frankel, 1998). Vidal-Valverde et al. (1993) observed that
-tocopherol in UHT milk stored at 308C decreased by 3-14% at 1 month
and by 9-30% at 2 months. On storage of UHT milk at -208C,
-toco-
pherol levels were stable for 2 months, but decreased by 10-20% after 4-8
months. Supplementation of animal feed with vitamin E increases the
oxidative stability of milk (Barrefors et al., 1995; Focant et al., 1998).
Elevated
-tocopherol levels contribute to lower lipid and cholesterol oxi-
dation in whole milk powders during storage at elevated temperatures
(McCluskey et al., 1997; Morrissey and Kiely, 2006).
12.4.6.
Vitamin E Status and Requirements
Vitamin E deficiency occurs only rarely in humans, and overt deficiency
symptoms in normal individuals consuming diets low in vitamin E have never
been described. However, it may occur in premature and some newborn
infants (Godell, 1989). When it occurs in older children and adults, it usually
arises as a consequence of malabsorption complicating cholestasis, abetali-
poproteinaemia, coeliac disease or cystic fibrosis (Sokol, 1993). There is also
an extremely rare disorder in which primary vitamin E deficiency occurs in
the absence of lipid malabsorption. Ataxia with isolated vitamin E deficiency
(AVED) is a rare autosomal recessive neurodegenerative disease character-
ized clinically by slowly progressive development of peripheral neuropathy,
spinocerebellar ataxia, dysarthria, the absence of deep tendon reflexes and
loss of proprioceptive and vibration sense (Mariotti et al., 2004). AVED is
caused by mutation in the
-TTP gene, which is located at chromosome 8q13
(Federico, 2004). Patients with AVED have serum vitamin E levels well below
the normal range [
<
2.5 mg/l, often
<
1 mg/l (normal range is 6-15 mg/l)]
(Koeing, 2003).
In general, there is no consensus as to the threshold concentration of
plasma or serum
-tocopherol at which people can be defined as having either
an inadequate or an acceptable vitamin E status (Morrissey and Sheehy,
1999). A recent prospective cohort study by Wright et al. (2006) showed
that increasing the circulating concentration of
-tocopherol up to
13-14 mg/l (30-33 mmol/l) was associated with significantly lower total
and cause-specific mortality in older male smokers, after which no further
benefit was noted. The estimated dietary vitamin E intake to achieve this
serum concentration may be as high as 15 mg/day (Traber, 2006), an amount
that could be obtained from dietary sources if a concerted effort was made to
eat foods rich in vitamin E (Gao et al., 2006; Traber, 2006). The Food and
