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Summary
In recent years, new physiological functions of vitamin A have
been identified in addition to its role in vision, namely its role in
immune defence reducing morbidity of measles, of respiratory and
possibly HIV infections, in gene regulation, in cell differentiation
and morphogenesis. With the discovery of nuclear receptors for
retinoic acid additional functions are likely to be found. The
recommended dietary allowances (RDA) for vitamin A, including
provitamin A carotenoids, vary greatly between countries. This may be
explained by difficulties in establishing needs: Homeostatic
mechanisms tightly control absorption, storage, release and transport
of vitamin A to target tissue, and plasma concentrations do not
reflect status unless there is vitamin A deficiency or excess. In the
United States RDAs were established on the basis of vitamin A
depletion-repletion studies with radio-labelled retinol. Intake
requirements were calculated to amount to 1000 mg retinol equivalents
(RE) for men, 800 mg RE for non-pregnant as well as pregnant women
and 1300 mg RE for lactating women. Dietary intake studies in
different countries have shown that it is in principle possible to
obtain these values from the diet either as preformed vitamin A or in
the form of provitamin A carotenoids or both. Risk groups for
inadequate intakes include low-income groups and younger persons
following weight-reducing and other unbalanced diets. Since
experience with recommended intake values in the United States has
been excellent, attempts at reducing these levels are unjustified and
should be resisted.
At intakes of up to three RDA values (~3000 mg RE) no unwanted
side-effects are to be expected. Even higher doses, if not taken
chronically, have been well tolerated, e.g. in deprived populations
with low liver reserves. The suggestion derived from a case-control
study that vitamin A taken at supplemental doses of 2400 mg RE may be
teratogenic have not been confirmed by several other studies. But it
is judicious to follow the recommendations of the American Pediatric
Society that women should not exceed a total daily intake of 3000 mg
RE.
In developing countries where acute and chronic vitamin A deficiency
is endemic causing xerophthalmia and blindness and increasing the
prevalence of infectious diseases and death in children, special
efforts are being made by WHO/UNICEF to provide programs for the
eradication of vitamin A deficiency by immediate treatment and by
long-term changes in dietary practices.
International Journal for Vitamin and Nutrition Research, 1997, Heft 2 © Verlag Hans Huber, Bern
Summary
a-Tocopherol (a-T) acts by different mechanisms: scavenging free oxygen radicals (FOR) and stabilizing membranes both may contribute to the prevention of the pathogenesis of diseases like cardiovascular events. The present work shows that a-T breaks the vicious cycle generated by damaged mitochondria. The latter stimulate the immune system increasing FOR formation that leads to more damaged mitochondria. a-T inhibits lipid peroxidation induced by recombinant human tumor necrosis factor (rh-TNF). Polymorphonuclear neutrophils (PMN) are activated by TNF to produce FOR causing lipid peroxidation of cardiomyocyte membranes. Since TNF is used as a therapeutic agent against certain tumors, treating patients with a-T could protect them against systemic side effects of TNF.
International Journal for Vitamin and Nutrition Research, 1997, Heft 2 © Verlag Hans Huber, Bern
Summary
The study undertook to ascertain the effect of a subnormal dietary
intake of vitamin B6 on plasma levels of total cholesterol, high
density lipoproteins, low density lipoproteins and triglycerides.
Plasma samples were assessed after 8 weeks in 3 groups of young male
Wistar rats receiving a daily pyridoxine hydrochloride intake of 60
(normal control group, A) and 20 mg (experimental group, C). Group B
was the pair-fed control. Vitamin B6 status of all groups was
confirmed by measuring plasma
pyridoxal-5'-phosphate and pyridoxal.
All groups were still in the growth phase at the end of 8 weeks, and
since the mean mass for all groups remained within the norm for male
Wistar rats, it would appear that caloric intake was not
compromised.
The fasting triglyceride levels in the normal control group were
significantly higher than those of the experimental and pair-fed
control groups, although all values remained within the normal range
for rats. A subnormal intake of
pyridoxine hydrochloride made no significant difference in the high
density lipoprotein levels although it contributed to a significant
increase in low density lipoprotein and total cholesterol levels. The
plasma pyridoxal-5'-phosphate and pyridoxal values were in accordance
with the pyridoxine hydrochloride intake of the different groups.
International Journal for Vitamin and Nutrition Research, 1997, Heft 2 © Verlag Hans Huber, Bern
Summary
Tissue zinc (Zn), copper (Cu) and iron (Fe) were determined in
three groups of young male Wistar rats that received a daily
pyridoxine hydrochloride (PN. HCl) intake of 45, 23 and 0 µg
respectively in their diets over 8 weeks.
No significant differences were found in the Zn and Cu levels in the
liver, kidney, skeletal and cardiac tissue of all 3 groups. The Fe
levels were significantly higher in the heart and liver and
significantly lower in the skeletal muscle of the group receiving no
PN. HCl in the diet (P < 0.05).
This study indicates that the increased fecal excretion of Zn and Cu
observed during a previous balance study on the above vitamin B6
deficient group of animals may be due to a decreased absorption of
these elements from the diet rather than their excretion from tissue
stores. The changes in Fe levels in the heart, liver and skeletal
muscle points towards some alteration in tissue stores of this
element during a vitamin B6 deficiency.
International Journal for Vitamin and Nutrition Research, 1997, Heft 2 © Verlag Hans Huber, Bern
Summary
We studied the effects of iron deficiency on the in vivo absorption (by using the intestinal perfusion technique in the duodenum) of different dietary sources of iron (haem, non-haem and equal parts of both forms) and investigated the interactions between iron and calcium, phosphorus, magnesium, copper and zinc in control and iron-deficient rats. Three perfusion solutions containing a different source of iron were used: solution 1, ferric citrate solution 2, haemoglobin solution 3, equal parts of ferric citrate and haemoglobin. We also tested the same perfusion solutions with 2,4-dinitrophenol (2,4-DNP), an inhibitor of oxidative phosphorylation (solutions 1-I, 2-I and 3-I). In control rats we observed three mechanisms of iron absorption: passive for soluble iron salts, active receptor-mediated for non-haem iron complexes, and active receptor-mediated for haem iron. In anaemic rats iron absorption was greater than in controls, except after perfusion with solution 2 (containing haemoglobin). Absorption increased as a result of both the passive and active, receptor-mediated mechanism for non-haem iron complexes. The active component was influenced by the depletion of haem receptors under severe iron deficiency. The absorption of calcium, copper and zinc in iron-deficient animals was lower than in controls, whereas phosphorus and magnesium absorption were not significantly affected. After perfusion with solution 2 or 3, calcium, copper and zinc absorption were lower than after solution 1. We conclude that ferropoenic anaemia in the rat impairs the absorptive process of those minerals that are absorbed, at the duodenal level mainly via active transport (haem iron, calcium, copper and zinc), but does not affect the active component involved in non-haem iron absorption.
International Journal for Vitamin and Nutrition Research, 1997, Heft 2 © Verlag Hans Huber, Bern
Summary
A nutritional survey of a Hungarian group of pregnant women was
carried out. One hundred and twenty nine women aged 25.9 years,
entered the study, but only 70 completed all the protocol. Average
body weight gain was 12.4 kg and the mean birth weight of the
newborns was 3,386 g.
Mean energy and nutrient intakes of pregnant women showed similar
patterns as in Hungarian non-pregnant women of the same age. The mean
energy intake was high (11 MJ), being 10% higher than for
non-pregnant women. The mean protein and lipid intakes were also
high, 91.9 g and 108.4 g, respectively, exceeding by 7% and 6% the
intakes of the non-pregnant women. Dietary intakes of saturated fatty
acids (SFAs) and monounsaturated fatty acids (MUFAs) were close to
12% of energy, and the intake of polyunsaturated fatty acids (PUFAs)
was 7.6% of total energy. Palmitic acid (16:0), oleic acid (18:1 n-9)
and linoleic acid (18:2 n-6) made the greatest contribution to the
total peak area of SFAs, MUFAs and PUFAs, respectively. The ratio of
P/S (polyunsaturated/ saturated fatty acids) was appropriate: 0.65
however, the ratio of linoleic acid (18:2 n-6), to linolenic acid
(18:3 n-3) was high: 16. The cholesterol intake was somewhat lower in
pregnant than in non-pregnant women. Complex carbohydrate intake was
low (245 g) but it was still by 75% higher than in non-pregnant
women.
The excess sodium intake (6.3 g) was very similar to that of
non-pregnant women. Mean values for retinol, tocopherol, ascorbic
acid, cobalamin and copper intakes were higher than the Hungarian
Recommended Dietary Allowances (RDA). Thiamine, riboflavin,
pyridoxine, niacin, calcium, iron and zinc intakes were
insufficient.
Data showed an imbalance in the energy and nutrient intakes of
Hungarian pregnant women, and this could be harmful for both the
mother and pregnancy outcome.
International Journal for Vitamin and Nutrition Research, 1997, Heft 2 © Verlag Hans Huber, Bern
Summary
The average dietary intake of coenzyme Q10 and coenzyme Q9 of the Danish population was determined, based on food consumption data from a national dietary survey. Selected food items in edible form were analyzed for the coenzyme Q content by HPCL with UV-detection, and their contribution to the total intake calculated. The effect of cooking was a 14&shyp32;% destruction of coenzyme Q10 by frying, and no detectable destruction by boiling. The average coenzyme Q10 intake of the Danish population was estimated to 3&shyp5mg;/day, primarily derived from meat and poultry (64% of the daily intake), while cereals, fruit, edible fats, and vegetables only make minor contributions. The intake of coenzyme Q9 is approximately 1mg/day, primarily derived from vegetable fats and cereals. The a-tocopherol content of the selected food samples was analyzed by HPLC with fluorescence detection, and the calculated average intake of a-tocopherol was comparable to the estimate from the dietary survey (7&shyp8; vs. 7.4mg a-tocopherol/day, respectively). The commercially available dietary supplements (capsules) provide 10&shyp30mg; CoQ10/day, thus substantially higher amounts than present in the average diet. The optimal dietary intake of coenzyme Q10 is unknown.
International Journal for Vitamin and Nutrition Research, 1997, Heft 2 © Verlag Hans Huber, Bern
Summary
Erythrocyte diene conjugate levels and glutathione peroxidase and superoxide dismutase activities were found unchanged in hypercholesterolemic subjects with plasma cholesterol levels above 240 mg/dl as compared to normocholesterolemics (below 200 mg/dl). However, the susceptibility of VLDL + LDL, apolipoprotein B containing lipoproteins to copper-induced peroxidation and plasma endogenous malondialdehyde levels were increased in hypercholesterolemics. These results indicate that hypercholesterolemia is associated with increased susceptibility of VLDL + LDL to lipid peroxidation.
International Journal for Vitamin and Nutrition Research, 1997, Heft 2 © Verlag Hans Huber, Bern