Elevated selenium (Se) intakes and calorie restriction (CR) inhibit mammary tumorigenesis in experimental animals. The present study was designed to investigate cell proliferation in the mammary tissue gland. Female weanling Sprague-Dawley rats were divided into 4 groups: control, 40% CR, 4 or 6 ppm Se in water as selenate. Control rats and Se rats were fed a control diet ad lib. CR rats were pair-fed 40% less than controls with a diet providing equal nutrients except carbohydrate calories. After 3 weeks, rats were injected with ({sup 3}H)-thymidine and killed 1 hr later. Se at 4 ppm significantly decreased only the number of ducts, whereas 6 ppm Se decreased both the number of ducts as well as the number and percent of labeled cells. CR had no effect on mammary cell proliferation. These results suggest that elevated Se intakes may protect against mammary tumorigenesis by decreasing cell proliferation, a mechanism which may affect the dose-response of the genotoxic chemicals frequently used as initiating agents in animal experiments.

To determine whether high dietary selenium intake was associated with adverse effects, selenium in diet, blood, and toenails was studied in relation to human health in adults residing in western South Dakota and eastern Wyoming. Over a 2-y period 142 subjects were recruited from households selected at random and from ranches where unusually high selenium intakes were suspected. Subjects completed health questionnaires, underwent physical examinations, provided blood samples for clinical assessment, and provided blood, urine, toenails, and duplicate-plate food collections for selenium analysis. About half of the 142 free-living subjects had selenium intakes greater than 2.54 mumol/d (200 micrograms/d) (range 0.86-9.20 mumol/d, or 68-724 micrograms/d). Physical findings characteristic of selenium toxicity were not present nor were clinically significant changes in laboratory tests or frequency of symptoms related to selenium in the blood, toenails, or diet. We found no evidence of toxicity from selenium in subjects whose intake was as high as 9.20 mumol/d (724 micrograms/d).

Because Se content of food varies widely, estimates of intake based on Se status are more accurate than those based on food composition tables. 77 free-living subjects from South Dakota and Wyoming, where the range of Se intake was large, provided blood, toenails, and 24-hour urines. Se intake, measured by chemical analysis of 4-8 days of duplicate-plate food composites from each subject, was estimated on the basis of the Se indices. To predict the natural logarithm of Se intake from serum Se the best fit was provided by : {minus}0.465 + 0.568{asterisk}SSe. Addition of lean body mass (LBM (kg)) and energy intake (EI (MJ)) to the model markedly improved the fit. Models based on Se in blood or urine gave slightly better estimates than those based on toenail Se. Consideration of data in addition to indices of Se status resulted in improved estimates of intake.

Duplicate meals, serum, whole blood, and toenails were collected every 3 mo for 1 y from a group of 44 free-living adults residing in high-selenium areas of South Dakota and Wyoming to assess the relation of selenium intake to indices of selenium status. The average selenium values for the group were as follows: dietary intake, 174 +/- 91 micrograms/d (mean +/- SD), 2.33 +/- 1.08 micrograms/kg body wt; serum, 2.10 +/- 0.38 mumol/L; whole blood, 3.22 +/- 0.79 mumol/L; and toenails, 15.2 +/- 3.0 nmol/g. Selenium intake (micrograms/kg body wt) was strongly correlated (all values, P less than 0.01) with selenium concentration of serum (r = 0.63), whole blood (r = 0.62), and toenails (r = 0.59). Men and women had similar mean values of serum, whole blood, and toenail selenium despite higher selenium intakes in men. Smokers had lower tissue selenium concentrations than did nonsmokers due, at least in part, to lower selenium intake. Age was not associated with tissue selenium content. Of the variables examined selenium intake was clearly the strongest predictor of tissue selenium concentration.