Chemistry Reference
In-Depth Information
risk factors. Compared with people in the lowest quartile of the ascorbate
distribution, those in the highest quartile had a 33% lower risk of coronary
artery disease, independent of other known risk factors, including age,
blood pressure, plasma lipids, cigarette smoking, body mass index and
diabetes.
Consistent evidence from epidemiological studies indicates that high
intakes of fruits and vegetables are associated with reduced risk of certain
cancers (Block et al., 1992; Steinmetz and Potter, 1996). Recent reports from
the United States (Loria et al., 2000) and the EPIC-Norfolk prospective study
(Khaw et al., 2001) suggest that men with a low serum ascorbate concentra-
tion may have an increased risk of mortality, probably because of an
increased risk of dying from cancer. In contrast, serum ascorbate concentra-
tion was not related to mortality among women.
12.6.6.
Vitamin C in Milk and Milk Products
The mean content of vitamin C in cow's milk is 2.11 mg/100 g (range
1.65-2.75 mg/100 g) (Walstra and Jenness, 1984), 5.48 mg/100 ml in goat's
milk (Kondyli et al., 2007), 2.49 mg/100 ml in camel's milk (Mehaia, 1994)
and 3.9 (
1.05) mg/100 ml (summer milk) and 3.02 (
2.01) mg/100 ml
(winter milk) in humans (Tawfeek et al., 2002). The mean concentration of
vitamin C in human milk is also affected by the stage of lactation and declined
from 6.18
0.09 mg/100 ml in colostrum to 4.68
0.1 mg/100 ml at 9 months
(Salmenpera, 1984). The influence of maternal vitamin C intake and its effect
on the vitamin C content of human milk has not been defined clearly. Byerley
and Kirksey (1985) observed that the vitamin C level in human milk did not
increase significantly in response to increasing maternal intake (up to tenfold)
of the vitamin. The authors proposed that a regulatory mechanism may be
present in mammary cells to prevent an elevation in the concentration of
vitamin C in milk beyond a certain saturation level. On the other hand, when
the intake of vitamin C is low, the level in breast milk is sensitive to supple-
mentation. Ortega et al. (1998) observed a relationship between ascorbic acid
intake and serum and milk levels. However, the changes in breast milk
ascorbate level were less pronounced than those in serum. The breast milk
ascorbate to serum ascorbate ratio decreased with increasing intake, and with
serum vitamin C level, which suggests that mammary tissue becomes satu-
rated with the vitamin when intake is high. The plasma concentration of
vitamin C in breast-fed infants was generally in the normal range, indicating
that exclusively breast-fed infants are well protected against vitamin C defi-
ciency (Salmenpera, 1984). Breast-fed infants appear to be capable of main-
taining a high plasma concentration of vitamin C independently of maternal
and milk concentrations.
