Chemical erosion of the Lilburn Cave system, Kings Canyon National Park, California.

Multi-year instrumental records for input, throughflow and output waters of the Lilburn Cave system provide control on denudation rates as they respond to seasonal and spatial variability. Data suggest that maximum denudation is in the late fall and early winter. This is when non-snowmelt discharge is at its maximum. At lower discharge rates the volume of water moving through the cave system is the limiting control on the volume of denudation. During periods of snowmelt the limiting control is the rate at which the calcite dissolves. This is probably the result of water flowing through wider channels during these times. Based on instrumental measurements, there is considerable variation in terms of where denudation occurs inside the cave. The loci of dissolution change from year to year. This is to be expected in the dynamic environment of the cave where materials shift routinely. This variability should be studied over longer periods of time in order to more fully understand its extent. The relatively small area of carbonate exposure relative to the area of the drainage basin gives rise to relatively high denudation rates. The carbonate is being removed at a rate of about 5000 metric tons per year, or at about 830 mm/y. This is about five times the rate reported in the humid karst regions of Malaysia. This information indicates that the relative proportion of carbonate in the drainage basin needs to be considered when trying to estimate denudation in other areas.

Zinc status and serum testosterone levels of healthy adults.

Zinc deficiency is prevalent throughout the world, including the USA. Severe and moderate deficiency of zinc is associated with hypogonadism in men. However, the effect of marginal zinc deficiency on serum testosterone concentration is not known. We studied the relationship between cellular zinc concentrations and serum testosterone cross-sectionally in 40 normal men, 20 to 80 y of age. In four normal young men (27.5 +/- 0.5 y), we measured serum testosterone before and during marginal zinc deficiency induced by restricting dietary zinc intake. We also measured serum testosterone in nine elderly men (64 +/- 9 y) who were marginally zinc deficient before and after 3 to 6 mo of supplementation with 459 mumol/ d oral zinc administered as zinc gluconate. Serum testosterone concentrations were significantly correlated with cellular zinc concentrations in the cross-sectional study (lymphocyte zinc versus serum testosterone, r = 0.43, p = 0.006; granulocyte zinc versus serum testosterone, r = 0.30, p = 0.03). Dietary zinc restriction in normal young men was associated with a significant decrease in serum testosterone concentrations after 20 weeks of zinc restriction (baseline versus post-zinc restriction mean +/- SD, 39.9 +/- 7.1 versus 10.6 +/- 3.6 nmol/L, respectively; p = 0.005). Zinc supplementation of marginally zinc-deficient normal elderly men for six months resulted in an increase in serum testosterone from 8.3 +/- 6.3 to 16.0 +/- 4.4 nmol/L (p = 0.02). We conclude that zinc may play an important role in modulating serum testosterone levels in normal men.

Zinc deficiency in elderly patients.

Zinc is needed for growth and development, DNA synthesis, neurosensory functions, and cell-mediated immunity. Although zinc intake is reduced in elderly people, its deficiency and effects on cell-mediated immunity of the elderly have not been established. Subjects enrolled in "A Model Health Promotion and Intervention Program for Urban Middle Aged and Elderly Americans" were assessed for nutrition and zinc status. One hundred eighty healthy subjects were randomly selected for the study. Their mean dietary zinc intake was 9.06 mg/day, whereas the recommended dietary allowance is 15 mg/day. Plasma zinc was normal, but zinc in granulocytes and lymphocytes were decreased compared with younger control subjects. Of 118 elderly subjects in whom zinc levels in both granulocytes and lymphocytes were available, 36 had deficient levels. Plasma copper was increased, and interleukin 1 (IL-1) production was significantly decreased. Reduced response to the skin-test antigen panel and decreased taste acuity were observed. Thirteen elderly zinc-deficient subjects were supplemented with zinc, and various variables were assessed before and after zinc supplementation. Zinc supplementation corrected zinc deficiency and normalized plasma copper levels. Serum thymulin activity, IL-1 production, and lymphocyte ecto-5'-nucleotidase increased significantly after supplementation. Improvement in response to skin-test antigens and taste acuity was observed after zinc supplementation. A mild zinc deficiency appears to be a significant clinical problem in free-living elderly people.

The use of behavioral contracting to increase exercise activity.

Abstract A cardiovascular risk reduction program used a submaximal treadmill stress test to evaluate physical fitness. Of the 179 individuals who participated in the health education counseling activities which followed testing, 96 signed a behavioral contract to engage in a 12-week aerobic exercise program. Forty-one contractors fully met contract goals, and 21 reported increased activity levels. Analyses examined demographic, risk factor, and attitudinal predictors of contract signing and contract adherence. Contract signing was related to education, smoking, and women's mean body weight. Only women's body weight was related to contract adherence. Attitudes toward exercise were related to neither. Level of contract adherence was significantly related to a decrease in exercising heart rate at the six-month follow-up assessment. These data suggest that contract signing may be a useful device for assessing client motivation and predicting program participation and behavioral change outcomes.

The physician's role in caries prevention.

The most cost-effective dental prevention occurs during infancy and childhood. The family physician, therefore, has a vital role in the prevention of dental caries by monitoring fluoride intake and being alert to the need for fluoride supplementation. Breast mild does not contain fluoride.