Effects of isoflavones on breast tissue and the thyroid hormone system in humans: a comprehensive safety evaluation.

Isoflavones are secondary plant constituents of certain foods and feeds such as soy, linseeds, and red clover. Furthermore, isoflavone-containing preparations are marketed as food supplements and so-called dietary food for special medical purposes to alleviate health complaints of peri- and postmenopausal women. Based on the bioactivity of isoflavones, especially their hormonal properties, there is an ongoing discussion regarding their potential adverse effects on human health. This review evaluates and summarises the evidence from interventional and observational studies addressing potential unintended effects of isoflavones on the female breast in healthy women as well as in breast cancer patients and on the thyroid hormone system. In addition, evidence from animal and in vitro studies considered relevant in this context was taken into account along with their strengths and limitations. Key factors influencing the biological effects of isoflavones, e.g., bioavailability, plasma and tissue concentrations, metabolism, temporality (pre- vs. postmenopausal women), and duration of isoflavone exposure, were also addressed. Final conclusions on the safety of isoflavones are guided by the aim of precautionary consumer protection.

Enrichment of eggs with n-3 polyunsaturated fatty acids: effects of vitamin E supplementation.

Eggs enriched with n-3 polyunsaturated fatty acids (PUFA) could contribute to dietary intake of these healthful fatty acids (FA). Because n-3 PUFA are highly susceptible to peroxidation, a first part of the study with Leghorn laying hens was carried out to investigate the influence of different levels of fish oil (0, 0.7, 1.4, 2.8, or 5.6%, respectively) in the diet on n-3 PUFA, cholesterol, vitamin E, and lipid peroxidation product contents in eggs. Addition of fish oil to a complete diet based on wheat, rye, tapioca, and soybean constituents containing 11 IU vitamin E/kg resulted in increased n-3 PUFA content in egg yolk, mainly due to accumulation of docosahexaenoic acid. Cholesterol was not altered up to 2.8% fish oil in the diet. The vitamin E content of the yolk was insufficient for the protection of PUFA from peroxidation. Addition of up to 2.8% fish oil to laying hen diets increased the n-3 PUFA content of yolks with a concomitant imbalance between vitamin E and PUFA, leading to increased levels of cytotoxic aldehydic lipid peroxidation products such as malondialdehyde (MDA). In a second part of the studies, the balance between vitamin E, PUFA, and lipid peroxidation was analyzed during the period of storage of n-3 PUFA-enriched eggs produced after feeding the laying hens with 1.5% fish oil diets with different concentrations of vitamin E (0, 5, 10, 20, 40, 80, 160 IU/kg). Storage of eggs resulted in a marked loss of vitamin E in yolk. In stored eggs, the cytotoxic lipid peroxidation products MDA, 4-hydroxynonenal, and 4-hydroxyhexenal were reduced in response to vitamin E supplementation. To prevent the increase of cytotoxic aldehydic lipid peroxidation during production and storage of n-3 PUFA-enriched eggs, a high vitamin E supplementation with at least 80 IU vitamin E/kg is needed.

Parenteral selenium supplementation in critically ill patients--effects on antioxidant metabolism.

Decreased plasma selenium (Se) levels are common in critically ill patients. Oxidative stress is regarded as one possible cause of the Se deficiency. We investigated in 20 critically ill patients with decreased plasma selenium concentrations the antioxidant metabolism during parenteral selenium supplementation (week 1: 2 x 500 micrograms; week 2:1 x 500 micrograms, week 3:3 x 100 micrograms sodium selenite). As marker of oxidative stress we measured the plasma malondialdehyde levels on days 0, 1, 3, 7, 14, and 21. The content of reduced and oxidized glutathione as well as the leucocyte activity marker elastase were estimated on the same days. Initial plasma Se levels were considerably decreased (0.44 +/- 0.1 mumol/l, mean +/- SEM). After one day of supplementation Se concentrations were in the reference range. Plasma malondialdehyde levels and the ratio of oxidized and reduced glutathione were initially elevated and decreased beginning on day 3 of supplementation. The mean elastase level was 113 +/- 10 micrograms/l on day 0. On day 3 elastase values decreased significantly (85 +/- 13 micrograms/l, p < 0.05; day 21, 19 +/- 7 micrograms/l, p < 0.001). Antioxidant metabolism showed significant changes beginning after 72 hours of therapy. This latency may be explained with the induction of the enzyme glutathione peroxidase. The lowered plasma Se concentrations measured in the critically ill patients and the significant effects on antioxidant metabolism during supplementation emphasized the importance of selenium administration in these patients.

Influence of Allium sativum on oxidative stress status - a clinical investigation.

The influence of daily application of coated garlic powder tablets (900 mg with an alliin content of 1.3% and an allicin content of 0.6%) on serum levels of malondialdehyde (MDA) and concentrations of reduced (GSH) and oxidized (GSSG) glutathione was investigated. 25 healthy volunteers were treated with garlic tablets for 2 months. After the 2 months' treatment a reduction of initial serum MDA level was observed. Application of Allium sativum reduced the MDA level by about 60% of the initial value. The MDA reducing effect was found in all age groups. In two age groups (younger than 30 years and older than 40 years) different initial values (higher values in elderly) but almost the equal MDA-levels after the treatment were found. The GSH concentration in circulating human erythrocytes showed a significant increase after the 2 month period of application of Allium sativum tablets, while the GSSG concentration showed no significant changes during the whole period of investigation. Thus a significantly decreasing trend of the GSSG: total glutathione ratio was measured.