Bibliotheca nutritio et dieta最新文献

In the presence of a chronically insufficient vitamin supply which was verified by repeated measurements of the vitamin parameters, many unfavorable psychometric findings in the corresponding deficiency groups are observed for the vitamins C, thiamin, riboflavin, cobalamin and folate, depending on the degree of the insufficient vitamin supply. Vitamin supplementation in cases of initially insufficient vitamin supply indicate some effects in the sense of an improvement of behavior and cognitive functions. Supplemental vitamin intake in physiological dosages in addition to a vitamin-sufficient diet did not lead to an improvement of behavior and mental performance.

Epidemiological surveys provided abundant evidence that under steady-state conditions diets rich in antioxidants (from vegetables/fruits and suitable vegetable oils) reduce the relative risk of premature death from CVD and cancer. Material relative risks seem to disappear at 'optimal' antioxidant plasma levels in the order of > or = 50 micromol/l vitamin C, > or = 30 micromol/l lipid-standardized vitamin E (alpha-tocopherol/cholesterol ratio > or = 5.1-5.2), > or = 2.2 micromol/l vitamin A, and > or = 0.4 micromol/l beta-carotene or > or = 0.4-0.5 micromol/l alpha-plus beta-carotene. Levels 25-35% below these thresholds predict an at least 2-fold higher risk. 'Suboptimal' levels of any single antioxidant may increase the relative risk independently. Accordingly, 'suboptimal' levels of several antioxidants predict a further increase of risk. Data on habitual voluntary multivitamin supplements providing an adequate supply of either vitamins A, C or E, and of beta-carotene in smokers, indicates that steady-state 'optimization' reduces more or less regularly the relative risk of CVD and cancer respectively. Simple counting of multivitamins regardless of their composition did not reveal any risk reduction. The antioxidant-related health benefits seem to depend on an adequacy of all antioxidants, and possibly of nonantioxidant nutrients as well. Thereby, an overall 'optimal' antioxidant defense system may be more important than excess of any particular 'magic bullet' antioxidant. Although antioxidants may represent a crucially important fraction within a health-maintaining diet, any nonantioxidant conutrients remain to be identified which could condition the health benefits of antioxidants. In randomized antioxidant intervention trials during 5-6 years in middle-aged to elderly subjects in China and Finland, only earlier stages of CVD and cancer respectively were prevented by rectifying previously poor levels. Correspondingly, the incidence of prostate cancer (developing mostly not until the male menopause) was reduced by correction of a previously poor vitamin E status in Finland. In contrast, irreversible precancerous lesions (such as esophageal dysplasia), clonically established common cancers (highly probable for the lung of elderly heavy smokers) as well as (presumably advanced, complicated) vascular lesions of chronic smokers did not respond favorably. (ABSTRACT TRUNCATED)

(1) Ascorbic acid has a key role in the absorption of dietary nonheme iron. (2) Natural and synthetic ascorbic acid have the same effect. (3) Ascorbic acid has a log/log dose-effect relationship in iron absorption. (4) The absorption is not reduced by prolonged intake of higher amounts of ascorbic acid. (5) There is a very efficient regulatory system for the absorption of iron preventing the development of dietary iron overload in normal subjects. (6) Each main meal should contain at least 50 mg ascorbic acid--more if a meal contains much phytate, and more if energy expenditure is low.

Consideration of the new evidence for changed nutrient requirements associated with aging raises the important issue of defining appropriate criteria for the selection of recommended vitamin intakes. Many of the criteria currently employed to establish dietary standards lack the sensitivity to detect subtle nutrition-sensitive alterations in metabolism with significant consequences for the aging process or place little weight on the risk factors of chronic diseases common among the elderly. It now appears possible to determine optimal levels of physiologic function for older age groups and design the nutrient intakes to achieve them. Further, the allowances for vitamins can now focus on intakes which not only prevent deficiency states but are associated with maximal risk reduction of chronic disease and disability.

Nutritional science is blossoming once more and the attempts by national or European Union communities to specify an appropriate diet for long-term health is becoming ever more difficult. The issue of antioxidants is also becoming very complex and it seems likely that over the next decade an integration of nutritional physiology, cell biology and epidemiology will allow us to produce a more coherent overview of the interplay between dietary bioactive molecules and the relative amount of antioxidant micronutrients. Once this understanding emerges then I foresee the need to revise--perhaps substantially--this first attempt by the SCF to produce European figures for the requirements for nutrients.