Expression of concern.

The Editor in Chief would like to alert readers to the following three articles published in Biological Trace Element Research.

Selenium and Alzheimer's disease: a systematic review.

Preventing Alzheimer's disease (AD) would require knowledge about its etiology to a degree of detail not yet available. The major hurdle in understanding the disease lies in teasing out the various causes and their complex interactions. Since considerable data have accrued showing that the essential trace element selenium (Se) might play different roles in the progression of AD, we conducted a systematic review of the literature regarding Se and AD.

Lead exposure: a contributing cause of the current breast cancer epidemic in Nigerian women.

Breast cancer incidence in Nigerian women has significantly increased during the past three decades in parallel with the rapid industrialization of that country. This suggested that the associated widespread contamination of the soil and of the water supplies by lead (Pb) and other industrial metals was a major contributing cause. Because of its many domestic, industrial, and automotive uses, Pb is of particular concern as it has been shown to promote the development of mammary tumors in murine mammary tumor virus-infected female C3H mice at levels as low of 0.

Selenium and cadmium levels and ratios in prostates, livers, and kidneys of nonsmokers and smokers.

Cadmium (Cd) from cigarette smoke, environmental, and nutritional sources accumulates in the human prostate where it interacts with selenium (Se) in a manner suggesting the formation of a 1:1 Cd-Se-protein complex. At low Cd exposures and adequate Se status, this interaction may be beneficial as it results in the detoxification of Cd. At higher exposures, Cd may weaken or abolish the anticarcinogenic effects of Se and increase prostate cancer risk.

Selenium in human and animal nutrition: resolved and unresolved issues. A partly historical treatise in commemoration of the fiftieth anniversary of the discovery of the biological essentiality of selenium, dedicated to the memory of Klaus Schwarz (1914-1978) on the occasion of the thirtieth anniversary of his death.

Selenium (Se) is an essential trace element unevenly distributed on the Earth's crust with low selenium regions predominating. To prevent selenium-deficiency diseases in livestock, additions of selenium to animal feed are required and were approved for all species, but the chemical form of the element to be added was not specified. Presently, sodium selenite is still widely employed, although it is not a natural nutritional form of selenium.

Selenium/cadmium ratios in human prostates: indicators of prostate cancer risk of smokers and nonsmokers, and relevance to the cancer protective effects of selenium.

Selenium (Se) in a large-scale human supplementation trial has been shown to significantly reduce the incidence of prostate cancer in elderly men. Because Se is known to interact with cadmium (Cd), it has been suggested that its cancer protective action could be attributable in part to its interaction with Cd, a toxic and suspected carcinogenic element, which is found in many foods, in drinking water, and in the environment. Cadmium is considered a significant prostate cancer risk factor as it stimulates the growth of prostate epithelial cells and promotes their malignant transformation.

The nutritional significance, metabolism and toxicology of selenomethionine.

SeMet is a naturally occurring toxic amino acid but at the same time represents the major nutritional source of selenium for higher animals and humans. The ability of SeMet to be incorporated into the body proteins in place of Met furthermore provides a means of reversible Se storage in organs and tissues. This property is not shared by any other naturally occurring selenoamino acid and thus could be associated with a specific physiological function of SeMet.

Lithium: occurrence, dietary intakes, nutritional essentiality.

Lithium is found in variable amounts in foods; primary food sources are grains and vegetables; in some areas, the drinking water also provides significant amounts of the element. Human dietary lithium intakes depend on location and the type of foods consumed and vary over a wide range. Traces of lithium were detected in human organs and fetal tissues already in the late 19th century, leading to early suggestions as to possible specific functions in the organism.