User:Selenocat/Selenium yeast

Selenium yeast, produced by fermenting Saccharomyces cerevisiae in a selenium-rich media, is a recognized source of organic food-form selenium. In this process, virtually all of the selenium structurally substitutes for sulfur in the amino acid methionine thus forming selenomethionine via the same pathways and enzymes that are used to form sulfur-containing methionine. Owing to its similarity to S-containing methionine, selenomethionine is taken up nonspecifically and becomes part of yeast protein. It is this metabolic route that makes selenium yeast valuable in animal and human nutrition, since it offers the same organic form of selenium produced by food-chain autotrophs (i.e., most plants and certain blue-green algae).

In the 1950s and 1960s, research first demonstrated selenium’s essential role in physiological processes.

Human health
Traditional dietary nutritional standards have been aimed at preventing nutrient deficiencies. However, a new paradigm for nutrition has emerged that supports the role that some nutrients play in maintaining good overall health and preventing or combating diseases such as Alzheimer’s disease, cancer, cardiovascular sclerosis, diabetes mellitus, hepatopathies, and viral infections. In particular, selenium has been long-recognized for its role in combating oxidative stress. To date, more than 30 selenoproteins have been identified in humans and studies have shown the importance of selenium status in the incidence and progression of many infectious and degenerative diseases. Consequently, re-evaluation of selenium dietary standards has occurred and is the subject of continued study.

Alzheimer’s disease (AD). Research has shown that dietary selenium yeast reduces amyloid β-peptide (Aβ) burden and minimizes DNA and RNA oxidation in the brains of knock-in mice expressing a Swedish familial amyloid precursor protein (APP) mutation and a humanized amyloid β-peptide (Aβ) and the 246L PS1 mutation. These animals develop amyloid plaques by 6 months of age and show impairment of hippocampal long-term potentiation. Deposition of Aβ in blood vessels is observed by 12 months of age and gradually increases. Alterations in Aβ solubility closely resembles that observed in patients with AD. Overall, researchers concluded that selenium yeast offers a potential therapeutic agent in neurologic disorders that involve increased oxidative stress.

Cancer. Epidemiological evidence supports an inverse relationship between selenium status and the risk of developing a wide variety of cancers or precancerous lesions. A double-blind, randomized, placebo-controlled clinical trial to test the effects of a selenium yeast supplement in patients with carcinoma of the skin had promising secondary endpoint results, showing it was associated with lower lung, colorectal, and prostate cancer incidence and in reduced lung cancer mortality. A Nutritional Prevention of Cancer trial showed a protective effect of selenium on nonmelanoma skin cancer incidence in response to selenium yeast supplementation using a male cohort with low selenium status on entry to the study. Similarly, selenium yeast supplementation, together with supplementation with beta carotene and vitamin E, were associated with reductions in total mortality, cancer mortality and incidence, especially of stomach cancer, over a 5.25-year period in nearly 15,000 persons in Linxian County, China.

In the Qidong Province in China, a population (about 2,474 families) at high-risk to develop hepatocellular carcinoma (HCC) received 200 μg Se/day in the form of selenium yeast; this group experienced a 35% reduction in liver cancer incidence. Moreover, in a subset of 226 hepatitis B antigen carriers, there was no incidence of HCC among half who were randomly assigned to receive 200 μg Se daily, whereas seven in a placebo group developed HCC.

Viral infection. Findings of increased viral virulence in selenium-deficient hosts support the need for further investigation into the interaction between host nutrition and viral evolutionary processes. Certain viral diseases have been shown to mutate more rapidly in selenium-deficient hosts producing more virulent viruses. This etiology has been demonstrated for both the Coxsackie B virus (associated with a Se-deficiency-related cardiomyopathy known as Keshan disease) and the influenza virus. Similarly, a study in the United Kingdom linked low selenium status with a decreased immune response to poliovirus vaccination and an increased mutation rate of the vaccine viral strain in feces. Selenium deficiency has also been linked with increased infectiousness of people with HIV-1.

High selenium yeast supplementation (200 μg/d) was evaluated in a 9-month double-blind, randomized, placebo-controlled trial in HIV-positive adult men and women. Daily supplementation was found to suppress progression of HIV-1 viral burden and provide indirect improvement to CD4 cell counts. (It is known that selenium status diminishes with HIV disease progression; low selenium status has been shown to be a predictor of HIV-related mortality. )

Animal feed and food-animal products
Selenium supplementation in yeast form has been shown to have beneficial effects in many species, especially on animal immune status, growth and reproduction    The consequent improvements in productivity can be of economic benefit to livestock producers for many reasons, including greater overall efficiency of feedstuff use.

Selenium yeast supplementation of food-animal diets has an added nutritional benefit to human consumers of food-animal products. Dietary selenomethionine-containing plant or yeast protein can be also stored nonspecifically in animal protein, which can result in nutritionally useful selenium content in meat, milk, and eggs. Consequently, strategies to supplement animal feed with selenium yeast have led to the development of selenium-rich functional foods, including selenium-enriched eggs and meats for human consumption.

Safety
Since 2000, selenium yeast (S. cerevisiae CNCM I-3060) has been reviewed and received the following approvals for use in animal and human diets: •	U.S. Food and Drug Administration (FDA) approval for use as a supplement to feed for chickens, turkeys, swine, goats, sheep, horses, dogs, bison, and beef and dairy •	European Food Safety Authority (EFSA) approval for use as a feed supplement for all animal species and categories. •	Organic Materials Review Institute approval for use as a feed supplement for all animal species. •	European Food Safety Authority (EFSA) approval for human health claims linking dietary intake of selenium yeast to “protection of DNA, proteins and lipids from oxidative damage, normal function of the immune system, normal thyroid function and normal spermatogenesis.” A review of the scientific literature concluded that selenium yeast from reputable manufacturers is adequately characterised, of reproducible quality, and shows no evidence of toxicity in long-term supplementation studies at doses as high as 400 and 800 micrograms per day (far above the EC tolerable upper intake level of 300 micrograms per day).

Analytical chemistry
Total selenium in selenium yeast can be reliably determined using open acid digestion to extract selenium from the yeast matrix followed by flame atomic absorption spectrometry. Determination of the selenium species selenomethionine can be achieved via proteolytic digestion of selenium yeast followed by high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS).

Categories
Selenium | Biology and pharmacology of chemical elements | Organoselenium compounds | Amino acids | Yeasts | Livestock | Food additives | Aquaculture | Food safety