Obesity and time to pregnancy.

BACKGROUND: Obesity may reduce fecundity. We examined the obesity-fecundity association in relation to menstrual cycle regularity, parity, smoking habits and age to gain insight into mechanisms and susceptible subgroups. METHODS: Data were provided by 7327 pregnant women enrolled in the Collaborative Perinatal Project at 12 study centres in the United States from 1959 to 1965. Prepregnancy body mass index (BMI) was analysed continuously and categorically [underweight (<18.5 kg/m2), optimal weight (18.5-24.9 kg/m2), overweight (25.0-29.9 kg/m2) and obese (>or=30.0 kg/m2)]. Adjusted fecundability odds ratios (FORs) were estimated using Cox proportional hazards modelling for discrete time data. RESULTS: Fecundity was reduced for overweight [OR=0.92, 95% confidence interval (95% CI): 0.84, 1.01] and obese (OR=0.82, 95% CI: 0.72, 0.95) women compared with optimal weight women and was more evident for obese primiparous women (OR=0.66, 95% CI: 0.49, 0.89). Fecundity remained reduced for overweight and obese women with normal menstrual cycles. Neither smoking habits nor age modified the association. CONCLUSIONS: Obesity was associated with reduced fecundity for all subgroups of women and persisted for women with regular cycles. Our results suggest that weight loss could increase fecundity for overweight and obese women, regardless of menstrual cycle regularity, parity, smoking habits and age.

Spatial analysis and mapping of sexually transmitted diseases to optimise intervention and prevention strategies.

OBJECTIVE: We analysed and mapped the distribution of four reportable sexually transmitted diseases, chlamydial infection/non-gonococcal urethritis (chlamydial infection), gonorrhoea, primary and secondary syphilis (syphilis), and HIV infection, for Wake County, North Carolina, to optimise an intervention. METHODS: We used STD surveillance data reported to Wake County, for the year 2000 to analyse and map STD rates. STD rates were mathematically represented as a spatial random field. We analysed spatial variability by calculating and modelling covariance functions of random field theory. Covariances are useful in assessing spatial patterns of disease locally and at a distance. We combined observed STD rates and appropriate covariance models using a geostatistical method called kriging, to predict STD rates and associated prediction errors for a grid covering Wake County. Final disease estimates were interpolated using a spline with tension and mapped to generate a continuous surface of infection. RESULTS: Lower incidence STDs exhibited larger spatial variability and smaller neighbourhoods of influence than higher incidence STDs. Each reported STD had a clustered spatial distribution with one primary core area of infection. Core areas overlapped for all four STDs. CONCLUSIONS: Spatial heterogeneity within STD suggests that STD specific prevention strategies should not be targeted uniformly across Wake County, but rather to core areas. Overlap of core areas among STDs suggests that intervention and prevention strategies can be combined to target multiple STDs effectively. Geostatistical techniques are objective, population level approaches to spatial analysis and mapping that can be used to visualise disease patterns and identify emerging outbreaks.

Hydrogen adsorption on the indium-rich indium phosphide (001) surface: a novel way to produce bridging In-H-In bonds.

The indium phosphide (001) surface provides a unique chemical environment for studying the reactivity of hydrogen toward the electron-deficient group IIIA element, indium. Hydrogen adsorption on the In-rich delta(2 x 4) reconstruction produced a neutral, covalently bound bridging indium hydride. Using vibrational spectroscopy and ab initio cluster calculations, two types of bridging hydrides were identified, a (mu-H)In(2) and a (mu-H)(2)In(3) "butterfly-like" structure. These structures were formed owing to the large thermodynamic driving force for adsorption of H atoms on solid-state indium dimers.

Experimental studies on human health effects of air pollutants. IV. Short-term physiological and clinical effects of nitrogen dioxide exposure.

Adult male volunteers were exposed to nitrogen dioxide (NO2) at 1.0 ppm in purified air under conditions simulating ambient photochemical smog exposures (2-hr exposure with intermittent light exercise at 31 degrees C and 35% relative humidity). Sham exposures to purified air alone served as controls. Exposure effects were assessed by pulmonary physiological tests and by a standardized clinical evaluation. No statistically physiological changes attributable to NO2 exposure were found except for a marginal loss in forced vital capacity after exposure on two successive days (1.5% mean decrease, P less than .05). Reported respiratory and other symptoms were slightly increased with exposure as compared to control, but the change was not significant. Short-term toxicity of NO2 at peak ambient concentrations appears to be substantially less than that of ozone in healthy people, but adverse NO2 effects in diseased people or in long-term exposures cannot be ruled out at present.

Effects of ozone exposure in Canadians and Southern Californians. Evidence for adaptation?

Comparison of published reports on physiological effects of exposure to ozone (O3) suggests that Canadians are more reactive than southern Californians. Responses of subjects and experimental methods were compared in a cooperative investigation of this apparent difference in reactivity. Four Canadians and four Californians were exposed to 0.37 ppm O3 in purified air at 21 degrees C and 50% relative humidity for 2 hours with intermittent light exercise. Exposures to purified air alone served as controls. Responses of subjects were similar to those observed previously: Canadians on the average showed greater clinical and physiological reactivity to exposure than did Californians, who were no more than minimally reactive. Canadians also showed larger increases in erythrocyte fragility following exposure. No methodological differences sufficient to explain different results of previous studies were found. Although other possible explanations have not been ruled out entirely, adaptation of southern Californians to chronic ambient O3 exposure is a rational hypothesis to explain these results.

Experimental studies on human health effects of air pollutants. III. Two-hour exposure to ozone alone and in combination with other pollutant gases.

Adult male volunteers were exposed to ozone (O3) at 0.25, 0.37, or 0.50 ppm, and to O3 in combination with nitrogen dioxide (NO2) and carbon monoxide (CO), with secondary stresses of heat, intermittent light exercise, and repeated exposure. Few important physiological changes, and only mild symptoms, were found with 0.25 ppm O3, with 0.25 ppm 03 plus 0.30 ppm NO2, or when 30 ppm CO was added to the latter mixture. With 0.37 ppm O3, more symptoms were present and some subjects developed definite decreases in pulmonary function. With 0.50 ppm O3, most subjects had symptoms and about half showed substantial pulmonary function decrement. In reactive subjects exposed on two successive days, changes were usually greater the second day, indicating that effects of successive exposures were cumulative.

Experimental studies on human health effects of air pollutants: I. Design considerations.

Because of the possible threat to public health posed by photochemical air pollution, a need exists for experimental studies of short-term respiratory effects of air pollutant exposure in humans. Such studies require rigorous control and comprehensive documentation of the experimental air environment and exposure conditions to ensure that results are both reliable and relevant to public health questions. In addition to biochemical, behavioral, and clinical evaluations, comprehensive pulmonary testing is required to assure that effects at different levels of the respiratory tract are detected. An experimental design based on these principles is described. Studies using this design have shown a wide range of sensitivity to the pollutant ozone and important adverse health effects in sensitive individuals under exposure conditions similar to those experienced during ambient pollution episodes.

A simplified method for study of RNA conformation--reaction of formylmethionine transfer RNA with [14C]methylamine-bisulfite.

A new chemical method for radioactive labeling of single-stranded regions of RNA has been used to probe the three-dimensional structure of E. coli tRNA(fMet) in solution. The procedure involves conversion of cytosine residues to N(4)-[(14)C]methylcytosines by treatment with (14)CH(3)NH(2) and sodium bisulfite at pH7. Ribonuclease digestion of the modified tRNA produces (14)C-labeled oligonucleotides which comigrate with the corresponding unlabeled oligonucleotides, facilitating structural analysis. By this procedure, E. coli tRNA(fMet) has been found to contain only six reactive cytosines: C(1), C(16), C(17), C(35), C(75) and C(76). In addition, slow reaction at C(m) (33) was observed. These results are in excellent agreement with previously reported data on the sites of exposed cytosine residues in tRNA(fMet) obtained by two other chemical methods. The methylamine-bisulfite procedure is recommended for studying the ordered structure of more complex polyribonucleotides such as viral and ribosomal RNAs.