Serum selenium and gastric cancer in two regions of Norfolk

Randomized controlled trial of the effect of selenium supplementation on thyroid function in the elderly in the United Kingdom

BACKGROUND

Thyroid function depends on the essential trace mineral selenium, which is at the active center of the iodothyronine deiodinase enzymes that catalyze the conversion of the prohormone thyroxine (T(4)) to the active form of thyroid hormone, triiodothyronine (T(3)).

OBJECTIVE

Because selenium intake in the United Kingdom has fallen during the past 25 y, we wanted to determine whether current selenium status might be limiting conversion of T(4) to T(3) in the elderly, in whom marginal hypothyroidism is relatively common.

DESIGN

We investigated the effect of selenium supplementation in a double-blind, placebo-controlled trial in 501 elderly UK volunteers. Similar numbers of men and women from each of 3 age groups, 60-64 y, 65-69 y, and 70-74 y, were randomly allocated to receive 100, 200, or 300 microg Se/d as high-selenium yeast or placebo yeast for 6 mo. As part of the study, plasma selenium, thyroid-stimulating hormone, and total and free T(3) and T(4) were measured. Data from 368 euthyroid volunteers who provided blood samples at baseline and 6 mo were analyzed.

RESULTS

Although selenium status at baseline correlated weakly with free T(4) (r = -0.19, P < 0.001) and with the ratio of free T(3) to free T(4) (r = 0.12, P = 0.02), we found no evidence of any effect of selenium supplementation on thyroid function, despite significant increases in plasma selenium. However, baseline plasma selenium in our study (x: 91 microg/L) was somewhat higher than in previous supplementation studies in which apparently beneficial effects were seen.

CONCLUSION

We found no indication for increasing selenium intake to benefit T(4) to T(3) conversion in the elderly UK population.

Impact of selenium on mood and quality of life: a randomized, controlled trial

BACKGROUND

Selenium is known to be important to the brain. Three small, published studies have suggested an effect of selenium supplementation or deprivation on mood in healthy volunteers. We investigated these findings on a much larger scale.

METHODS

In this double-blind, placebo-controlled intervention, 501 UK participants aged 60-74 were randomly allocated to receive 100, 200 or 300 microg selenium/d as high-selenium yeast or placebo yeast. Mood (Profile of Moods States - Bipolar Form [POMS-BI] questionnaire), "quality of life" (Short Form 36 [SF-36] questionnaire) and plasma selenium were measured at baseline and six months.

RESULTS

Supplementation significantly increased plasma selenium above baseline values: from an overall mean (SD) of 90(19) ng/g to 91(26), 144(27), 191(41) and 227(53) ng/g in the placebo, 100, 200, 300 microg selenium groups respectively (p < .001). Four hundred forty-eight participants completed the POMS-BI questionnaires at both time points, with no significant differences in total mood or mood-subscale scores seen between doses. After six months of supplementation, mean (SD) total mood scores for the four doses were 163(36), 161(37), 162(33), 162(34), F(3,443) = .25, p = .86. Quality of life was similarly unaffected.

CONCLUSIONS

There was no evidence that selenium supplementation benefited mood or quality of life in these elderly volunteers. Though this is at odds with some previous results, our robust study design, much larger sample size and longer supplementation period, together with the evidence that the brain is a privileged site for selenium retention, suggest that this is a reliable finding.

The antioxidant role of selenium and seleno-compounds

Selenium (Se) is an essential trace element for animals and humans that is obtained from dietary sources including cereals, grains and vegetables. The Se content of plants varies considerably according to its concentration in soil. Plants convert Se mainly into Se-methionine (Se-Met) and incorporate it into protein in place of methionine (Met). Selenocystine (Se-Cys), methyl-Se-Cys and gamma-glutamyl-Se-methyl-Cys are not significantly incorporated into plant protein and are at relatively low levels irrespective of soil Se content. Higher animals are unable to synthesize Se-Met and only Se-Cys was detected in rats supplemented with Se as selenite. Renal regulation is the mode by which whole body Se is controlled. Se is concentrated in hair and nail and it occurs almost exclusively in organic compounds. The potentiating effect of Se deficiency on lipid peroxidation is enhanced in some tissues by concurrent deficiency of copper or manganese. In the in vitro system, the chemical form of Se is an important factor in eliciting cellular responses. Although the cytotoxic mechanisms of selenite and other redoxing Se compounds are still unclear, it has been suggested that they derive from their ability to catalyze the oxidation of thiols and to produce superoxide simultaneously. Selenite-induced cytotoxicity and apoptosis in human carcinoma cells can be inhibited with copper (CuSO(4)) as an antioxidant. High doses of selenite result in induction of 8-hydroxydeoxyguanosine (8-OHdG) in mouse skin cell DNA and in primary human keratinocytes. It may cause DNA fragmentation and decreased DNA synthesis, cell growth inhibition, DNA synthesis, blockade of the cell cycle at the S/G(2)-M phase and cell death by necrosis. In contrast, in cells treated with methylselenocyanate or Se methylselenocysteine, the cell cycle progression was blocked at the G(1) phase and cell death was predominantly induced by apoptosis.

Relationship between mineral and trace element concentrations in drinking water and gastric cancer mortality in Japan

It is well known that the incidence and mortality from gastric cancer in Japan are the highest in the world. This is thought to be due, in part, to dietary habit, including a high salt intake. There are, however, no epidemiological reports to describe the relationship between ingestion of mineral and trace elements and gastric carcinogenesis. In this study, we determined the concentrations of 14 elements in drinking water from 34 water treatment plants in Aomori Prefecture, Japan, and studied how element concentrations were geographically associated with gastric cancer mortality rate. Gastric cancer mortality was calculated from the data of the Annual Aomori Health Report. Multiple regression analysis (stepwise method of decreasing the number of variables) was performed by using age-adjusted mortality of gastric cancer by gender as objective variables and each element concentration as an explanatory variable. The standardized partial regression coefficient was significant in men for zinc (-0.59, P = 0.004), lead (1.01, P = 0.013), strontium (1.23, P = 0.007), and selenium (-1.62, P = 0.004), whereas it was significant in women for lead (-0.65, P = 0.022), strontium (0.51, P = 0.035), and gold (0.70, P = 0.019). It is suggested that selenium and zinc may aid in the prevention of gastric carcinogenesis. However, the significant relationship of sodium (a component of salt) to gastric carcinogenesis was not observed, although many previous epidemiological studies in Japan have shown this relationship.