Protective factors relating to decreased risks of adolescent suicidal behaviour.

BACKGROUND: Suicide has been identified as one of the three leading causes of death in adolescents and young adults. No previous study in China has tested the association between protective factors and urban adolescents' suicidal behaviours. In this study we tested the hypothesis that suicidal behaviours would be associated with multiple protective factors. METHODS: A stratified random of 9015 students from 100 junior middle schools in Beijing, Hangzhou, Wuhan and Urumqi completed the Chinese version of Global School-Based Student Health Survey. RESULTS: Overall, 17.4% of students had seriously considered attempting suicide, and 8.1% had made a specific plan to attempt suicide during the 12 months preceding the survey. The students in Wuhan (18.7%) and Urumqi (20.8%) cities were significantly more likely than students in Beijing (14.4%) and Hangzhou (14.4%) to have suicidal ideation (chi2 = 45.9, P < 0.001). Female students were significantly more likely than male students to have suicidal ideation and have made suicide attempts [odds ratio (OR) = 1.4, P < 0.001]. Results indicated that the rates of suicidal ideation and suicide attempts increased with age (OR = 1.44, P < 0.001). Multivariate logistic regression models showed that suicide risk tended to decrease significantly when 'days of missed classes or school without permission were less than one', and when students thought students in their school were kind and helpful most of the time or always', 'parents or guardians checked to see if homework was done most of the time or always', 'parents or guardians understood their problems and worries most of the time or always' and 'parents or guardians really know what they are doing with their free time most of the time or always'. CONCLUSIONS: Adolescent suicide behaviour should be a serious problem. Measures can be taken to prevent suicide by observing the factors significantly linked to suicidal behaviour. Steps can then be taken to identify adolescents who have serious suicidal ideation so that intervention can be taken to reduce the suicidal rate.

Neutral and non-neutral evolution of Drosophila mitochondrial DNA.

To test hypotheses of neutral evolution of mitochondrial DNA (mtDNA), nucleotide sequences were determined for 1515 base pairs of the NADH dehydrogenase subunit 5 (ND5) gene in the mitochondrial DNA of 29 lines of Drosophila melanogaster and 9 lines of its sibling species Drosophila simulans. In contrast to the patterns for nuclear genes, where D. melanogaster generally exhibits much less nucleotide polymorphism, the number of segregating sites was slightly higher in a global sample of nine ND5 sequences in D. melanogaster (s = 8) than in the nine lines of D. simulans (s = 6). When compared to variation at nuclear loci, the mtDNA variation in D. melanogaster does not depart from neutral expectations. The ND5 sequences in D. simulans, however, show fewer than half the number of variable sites expected under neutrality when compared to sequences from the period locus. While this reduction in variation is not significant at the 5% level, HKA tests with published restriction data for mtDNA in D. simulans do show a significant reduction of variation suggesting a selective sweep of variation in the mtDNA in this species. Tests of neutral evolution based on the ratios of synonymous and replacement polymorphism and divergence are generally consistent with neutral expectations, although a significant excess of amino acid polymorphism within both species is localized in one region of the protein. The rate of mtDNA evolution has been faster in D. melanogaster than in D. simulans and the population structure of mtDNA is distinct in these species. The data reveal how different rates of mtDNA evolution between species and different histories of neutral and adaptive evolution within species can compromise historical inferences in population and evolutionary biology.

Sexually antagonistic cytonuclear fitness interactions in Drosophila melanogaster.

Theoretical and empirical studies have shown that selection cannot maintain a joint nuclear-cytoplasmic polymorphism within a population except under restrictive conditions of frequency-dependent or sex-specific selection. These conclusions are based on fitness interactions between a diploid autosomal locus and a haploid cytoplasmic locus. We develop a model of joint transmission of X chromosomes and cytoplasms and through simulation show that nuclear-cytoplasmic polymorphisms can be maintained by selection on X-cytoplasm interactions. We test aspects of the model with a "diallel" experiment analyzing fitness interactions between pairwise combinations of X chromosomes and cytoplasms from wild strains of Drosophila melanogaster. Contrary to earlier autosomal studies, significant fitness interactions between X chromosomes and cytoplasms are detected among strains from within populations. The experiment further demonstrates significant sex-by-genotype interactions for mtDNA haplotype, cytoplasms, and X chromosomes. These interactions are sexually antagonistic--i.e., the "good" cytoplasms in females are "bad" in males--analogous to crossing reaction norms. The presence or absence of Wolbachia did not alter the significance of the fitness effects involving X chromosomes and cytoplasms but tended to reduce the significance of mtDNA fitness effects. The negative fitness correlations between the sexes demonstrated in our empirical study are consistent with the conditions that maintain cytoplasmic polymorphism in simulations. Our results suggest that fitness interactions with the sex chromosomes may account for some proportion of cytoplasmic variation in natural populations. Sexually antagonistic selection or reciprocally matched fitness effects of nuclear-cytoplasmic genotypes may be important components of cytonuclear fitness variation and have implications for mitochondrial disease phenotypes that differ between the sexes.

Competitive foods and beverages available for purchase in secondary schools--selected sites, United States, 2004.

School Health Profiles is conducted biennially to assess characteristics of school health programs. State and local departments of education and health select either all public secondary schools within their jurisdictions or a systematic, equal-probability sample of public secondary schools to participate in School Health Profiles. At each school, the principal and lead health education teacher were sent questionnaires to be self-administered and returned to the state or local agency conducting the survey. In 2004, a total of 27 states and 11 large urban school districts obtained weighted data from their survey of principals. The findings in this report indicate that the majority of secondary schools in 27 states and 11 large urban school districts allow students to purchase snack foods or beverages from vending machines or at the school store, canteen, or snack bar. The types of competitive foods and beverages available for purchase varied across states and large urban school districts. Overall, fruits or vegetables were less likely to be available for purchase than the other types of foods or beverages. Bottled water and soft drinks, sports drinks, or fruit drinks that are not 100% juice were most likely to be available for purchase.

Gene flow versus local adaptation in the northern acorn barnacle, Semibalanus balanoides: insights from mitochondrial DNA variation.

In reciprocal transplant experiments, Bertness and Gaines (1993) found that Semibalanus balanoides juveniles that had settled in an upper Narragansett Bay estuary survived better in that estuary that did juveniles from coastal localities. The observed pattern of survivorship led to the claim that local adaptation may result from a combination of limited gene flow between and strong selection within these habitats. Here we test the hypothesis that limited gene flow has led to habitat-specific population differentiation using sequence and restriction fragment length polymorphism analyses of the mitochondrial DNA D-loop region of S. balanoides. Samples were analyzed from replicated coastal and estuary localities in both Narragansett Bay, Rhode Island, and Damariscotta River, Maine. The patterns of F(ST) indicate that gene flow between coast and estuary is extensive (Nm > 100) and is not lower in the estuary with lower flushing rates (Narragansett Bay). Given the high estimate of genetic exchange, adaptations for unpredictable environments seem more likely than local adaptation in this species because loci that respond to selection in one generation are essentially homogenized by the next seasons' settlement. Nevertheless, these estimates of neutral gene flow can help identify the strength of selection necessary for local adaptation to accumulate in Semibalanus.

Health-risk behaviors among our nation's youth: United States, 1992.

This report presents national estimates of the prevalence of selected health risk behaviors among youth ages 12-21 years, by sex, Hispanic origin, and race for youth of non-Hispanic origin. Topics include: cigarette and other tobacco use, alcohol and other drug use, sexual experience, HIV/AIDS education, runaway and homeless experiences, violence, unintentional injury control, weight control, and participation in physical activities. Data are from the 1992 National Health Interview Survey's Youth Risk Behavior Survey.

Physical activity patterns in American high school students. Results from the 1990 Youth Risk Behavior Survey.

OBJECTIVE: To assess by self-reported participation in vigorous physical activity, the quantity and quality of school physical education, team sports, and television watching among 11,631 American high school students. RESULTS: Of all students in grades 9 through 12, 37% reported engaging in 20 minutes of vigorous physical activity three or more times per week. Participation in vigorous physical activity was higher among boys than girls (P < .01) and higher among white students than among those of other races and ethnic groups (P < .01). Overall, 43.7% of boys and 52% of girls reported that they were not enrolled in physical education classes. Of the students who reported attending physical education class during the past 2 weeks, 33.2% reported exercising 20 minutes or more in physical education class three to five times per week. In contrast, rates of participation in varsity and junior varsity sports remained constant across grade levels, but participation in recreational physical activity programs showed a lesser magnitude and also decreased with advancing grade. More than 70% of students reported spending at least 1 hour watching television each school day, and more than 35% reported watching television 3 hours or more each school day. CONCLUSIONS: Participation in vigorous physical activity and physical education class time devoted to physical activity are substantially below the goals set in Healthy People 2000. As students move toward graduation, we observed disturbing declines in participation in community recreation programs and overall vigorous activity. Students appear to spend considerably more time watching television than participating in physical activity. Public health efforts should focus on increasing the physical activity levels of our youth to enhance their current well-being and to reduce the risks of future chronic disease.

Weapon-carrying, physical fighting, and fight-related injury among U.S. adolescents.

INTRODUCTION: Access to firearms and other weapons has been cited as an important factor contributing to the rise in violence-related injury among adolescents in the United States. METHODS: Data from the Youth Risk Behavior Survey supplement to the 1992 National Health Interview Survey were analyzed to examine relationships among weapon-carrying, physical fighting, and fight-related injury among U.S. adolescents aged 12-21 years (N = 10,269). Adjusted odds ratios (OR) were used to describe the association of weapon-carrying during the past 30 days with physical fighting and fight-related injury during the past 12 months. RESULTS: Weapon-carrying (15%) and physical fighting (39%) were common among adolescents. One out of 30 (3.3%) adolescents reported receiving medical care for fight-related injuries. Controlling for demographic characteristics, youth who carried weapons were more likely than those who did not to have been in a physical fight (OR = 3.3). The association between weapon-carrying and physical fighting was stronger among females (OR = 5.0) than among males (OR = 2.9), but did not vary significantly by age, race/ethnicity, or place of residence (urban, suburban, rural). Controlling for frequency of physical fighting and demographics, adolescents who carried a handgun (OR = 2.6) or other weapon (OR = 1.6) were more likely than those who did not carry a weapon to have had medical care for fight-related injuries. CONCLUSIONS: Among adolescents, weapon-carrying is associated with increased involvement in physical fighting and a greater likelihood of injury among those who do fight. Efforts to reduce fight-related injuries among youth should stress avoidance of weapon-carrying.

Physical activity, food choice, and weight management goals and practices among US college students.

INTRODUCTION: Physical activity and a healthy diet have been recommended to help reverse the increasing prevalence of overweight among adolescents and adults in the United States. METHODS: Data is from the 1995 National College Health Risk Behavior Survey. A representative sample of US undergraduate college students (n = 4609) were analyzed to examine associations of physical activity and food choice with weight management goals and practices. RESULTS: Based on self-reported height and weight, 35% of students were overweight or obese (body mass index > or = 25.0). Nearly half (46%) of all students reported they were trying to lose weight. Female students were less likely than male students to be overweight, but more likely to be trying to lose weight. Among female and male students, using logistic regression to control for demographics, trying to lose weight was associated with participation in vigorous physical activity and strengthening exercises, and consumption of < or = 2 servings/ day of high-fat foods. Female and male students who reported using exercise to lose weight or to keep from gaining weight were more likely than those who did not to participate in vigorous, strengthening, and moderate physical activity, and were more likely to eat > or = 5 servings/day of fruits and vegetables and < or = 2 servings/day of high-fat foods. Among students who were trying to lose weight, only 54% of females and 41% of males used both exercise and diet for weight control. CONCLUSION: Colleges should implement programs to increase student awareness of healthy weight management methods and the importance of physical activity combined with a healthy diet.

Trends in risk behaviors for HIV infection among U.S. high school students, 1989-1991.

The objective of this study was to examine trends in rates of self-reported HIV-related instruction and behaviors among high school students in the United States. Self-administered questionnaires were completed by three independent, multistage national probability samples of public and private school students in grades 9 through 12 who were surveyed in the spring of 1989, 1990, and 1991, respectively. Controlling for demographic characteristics, we used logistic regression to test for trends from 1989 to 1991. From 1989 to 1991, the proportion of students who had received HIV instruction in school significantly increased from 53.7% in 1989 to 83.3% in 1991. At the same time, the proportion of students engaging in selected sexual behaviors generally decreased. We found significant declines in the proportion of students who had engaged in sexual intercourse (58.5% in 1989 to 54.1% in 1991), had two or more sex partners during their lifetime (40.1% in 1989 to 35.2% in 1991), and had four or more lifetime sex partners (23.6% in 1989 to 18.7% in 1991). School-based HIV instruction, which is reaching greater numbers of U.S. students, may be contributing to the decline in reported risk behavior. However, because the current level of HIV-related behavior is still too high, risk-reduction efforts for adolescents should be maintained and strengthened.

Prevalence of health-related behaviors among alternative high school students as compared with students attending regular high schools.

PURPOSE: To provide national data on health-risk behaviors of students attending alternative high schools and compare the prevalence of these risk behaviors with data from the 1997 national Youth Risk Behavior Survey. METHODS: The national Youth Risk Behavior Survey uses a three-stage cluster sampling design. Data were collected from 8918 students in alternative high schools in 1998 (ALT-YRBS) and 16,262 students in regular high schools in 1997 (YRBS). The health-risk behaviors addressed include behaviors that contribute to unintentional injuries and violence, tobacco use, alcohol and other drug use, sexual behaviors, unhealthy dietary behaviors, and physical inactivity. A weighing factor was applied to each student record to adjust for nonresponse and varying probabilities of selection. SUDAAN was used to compute 95% confidence intervals, which were considered significant if the 95% confidence intervals did not overlap. RESULTS: Students attending alternative high schools were at significantly greater risk than students in regular high schools for violence-related injury; suicide; human immunodeficiency virus infection or other sexually transmitted diseases; pregnancy; and development of chronic disease related to tobacco use, unhealthy dieting practices, and lack of vigorous activity. CONCLUSIONS: Many students in alternative high schools are at risk for both acute and chronic health problems. Because these youth are still in a school setting, alternative high schools are in a unique position to provide programs to help decrease the prevalence of risk-taking behaviors.

Prevalence of health risk behaviors among Asian American/Pacific Islander high school students.

PURPOSE: [corrected] To compare the prevalence of selected risk behaviors among Asian American/Pacific Islander (AAPI) students and white, black, and Hispanic high school students in the United States. METHODS: The national Youth Risk Behavior Survey conducted in 1991, 1993, 1995, and 1997 by the Centers for Disease Control and Prevention produced nationally representative samples of students in grades 9 through 12 in all 50 states and the District of Columbia. To generate a sufficient sample of AAPI students, data from these four surveys were combined into one dataset yielding a total sample size of 55, 734 students. RESULTS: In the month preceding the survey, AAPI students were significantly less likely than black, Hispanic, or white students to have drunk alcohol or used marijuana. AAPI students also were significantly less likely than white, black, or Hispanic students to have had sexual intercourse; however, once sexually active, AAPI students were as likely as other racial or ethnic groups to have used alcohol or drugs at last intercourse or to have used a condom at last intercourse. AAPI students were significantly less likely than white, black, or Hispanic students to have carried a weapon or fought but were as likely as any of the other groups to have attempted suicide. CONCLUSIONS: A substantial percentage of AAPI students engage in risk behaviors that can affect their current and future health. Prevention programs should address the risks faced by AAPI students using culturally sensitive strategies and materials. More studies are needed to understand the comparative prevalence of various risk behaviors among AAPI subgroups.

Other substance use among high school students who use tobacco.

PURPOSE: To examine relationships between tobacco use and use of other substances among U.S. high school students, by gender and racial/ethnic subgroups. METHODS: Data about tobacco and other substance use were analyzed from the 1995 national Youth Risk Behavior Survey implemented by the Centers for Disease Control and Prevention. RESULTS: Compared to nonsmokers, current smokers were significantly more likely to report use of all other substances we examined, including lifetime use of cocaine, inhalants, other illegal substances, and multiple substances and current alcohol use, episodic heavy drinking, marijuana use, and cocaine use. A strong dose-dependent relationship between current cigarette smoking and other substance use was identified. Among smokeless tobacco users, a strong dose-dependent relationship was found for all examined substances with the exception of lifetime and current cocaine use. Finally, a pattern of risk emerged suggesting that the likelihood of other substance use increases as students move from no tobacco use to smokeless tobacco use only, to cigarette smoking only, and to use of both smokeless tobacco and cigarettes. CONCLUSIONS: Programs designed to prevent tobacco or other substance use should consider that such use often occurs concomitantly.

Use of birth control pills, condoms, and withdrawal among U.S. high school students.

PURPOSE: To examine the use of contraception at last sexual intercourse among currently sexually active adolescents. METHODS: We analyzed data from national school-based Youth Risk Behavior Surveys (YRBS) conducted in 1991, 1993, 1995, and 1997. The YRBS is a self-administered, anonymous survey which uses a national probability sample of U.S. students in public and private schools from grades 9 through 12. RESULTS: From 1991 to 1997, condom use significantly increased (from 46% to 57%), birth control pill use decreased (from 21% to 17%), and use of withdrawal significantly decreased (from 18% to 13%). In 1997, although more students were using condoms, 13% reported using withdrawal and 15% reported using no method to prevent pregnancy at last sexual intercourse. In 1997, condom use among females was significantly lower in the 9th grade than in the 12th grade (p <.001), whereas birth control pill use was higher (p <.001) and use of withdrawal remained stable. Among males, condom use and withdrawal use remained stable from 9th to 12th grade, whereas birth control pill use by their partner increased (p <.001). CONCLUSIONS: Inadequate contraceptive use among sexually active adolescents continues to be a major public health problem in the United States. For young people who will not remain sexually abstinent, families, health care providers, schools, and other influential societal institutions should promote the correct and continued use of condoms as essential protection against sexually transmitted diseases and human immunodeficiency virus infection.

Contextual influences on school provision of health services.

PURPOSE: To examine contextual factors that may facilitate or impede the provision of school health services. METHODS: Using a composite database derived primarily from the National Longitudinal Study of Adolescent Health, we used logistic regression to examine how selected characteristics of communities, schools, and state-level policies are related to the provision of specific health services by high schools. RESULTS: Schools whose students experienced more health risks were generally more likely to provide related services than schools whose students experienced fewer risks. State policies and requirements for health-related programs and services were associated with greater school-based provision of services. Availability of health care services within the community was associated with a reduced likelihood that schools provided similar services on-site; however, for some health services, the reverse was true. In general, more affluent communities were more likely to provide school health services than less affluent communities. Public schools were more likely to offer health services than private schools. CONCLUSIONS: Certain characteristics of communities, schools, and state-level policies are associated with the provision of school health services. These contextual factors appear to operate by creating a demand for services and by creating the opportunity for schools to provide health services.

Age of initiating selected health-risk behaviors among high school students in the United States.

PURPOSE: To estimate and compare the age of initiation of alcohol use, cigarette smoking, sexual intercourse, and marijuana use among female and male students in U.S. high schools. METHODS: Using data from the 1991 and 1993 national school-based Youth Risk Behavior Surveys, life-table analysis was used to create hypothetical cohorts to estimate age of initiation of selected health-risk behaviors. The sample size was 12,272 in 1991 and 16,296 in 1993, with an overall response rate of 68% in 1991 and 70% in 1993. RESULTS: Male students initiate each of these behaviors earlier than female students, but the pace of initiation for females accelerates so that by age 15 years the cumulative proportion of male and female students who have initiated these behaviors is similar. For both female and male students, the youngest cohort appears to initiate use of alcohol and sexual intercourse at earlier ages than older cohorts. Similarly, the younger cohorts of female students appear to initiate smoking cigarettes and using marijuana at earlier ages than older cohorts. CONCLUSIONS: Many high school students are initiating alcohol use, cigarette smoking, sexual intercourse, and marijuana use at early ages. These data suggest a need for intensive intervention programs by middle/junior high school to motivate and prepare students to avoid these behaviors. Clinicians should begin screening and counseling for risk behaviors in early adolescence.

Progress in efforts to prevent the spread of HIV infection among youth.

The Human Immunodeficiency Virus (HIV) that causes AIDS will continue to threaten public health for years to come. Despite some popular misperceptions, adolescents are at risk of infection. Twenty percent of persons reported with AIDS have been ages 20 through 29. Given the long incubation period between HIV infection and AIDS, some of these young adults probably were infected while they were teenagers. Young people must develop the skills they will need to avoid HIV infection and other related health problems. In 1987, the Centers for Disease Control (CDC) launched a national program to help schools and other agencies that serve youth across the nation provide effective health education to prevent the spread of HIV. CDC supports and works closely with national health and education organizations, State and local education agencies, colleges and universities, and local health departments to establish HIV prevention policies and programs, training and demonstration centers, information development and dissemination activities. The impact of these efforts are assessed through applied surveillance and evaluation research. Through this system, CDC is attempting to institutionalize the means for continuously providing educational programs that will be effective in preventing HIV infection and other important health problems.

The Youth Risk Behavior Surveillance System: measuring health-risk behaviors.

OBJECTIVE: To measure priority health-riskbehaviors among youth. METHODS: The Youth Risk Behavior Surveillance System (YRBSS) monitors priority health-risk behaviors among youth. RESULTS: In 1999, many high school students practiced behaviors that contribute to leading health problems--16.4% rarely or never wore safety belts and, during the past 30 days, 17.3% carried a weapon, 34.8% smoked cigarettes, and 26.7% used marijuana. Also, 49.9% had had sexual intercourse. One quarter (26.0%) were at risk for becoming overweight or were overweight. CONCLUSION: YRBSS data are used to improve policies and programs to reduce priority health-risk behaviors among youth.

Smoking initiation and smoking patterns among US college students.

The ages at which 18- to 24-year-old college students started smoking and its relationship to subsequent smoking were explored, using data from the 1995 National College Health Risk Behavior Survey. Most students (70%) had tried smoking; among those who had tried, 42% were current smokers, 19% were current frequent smokers, and 13% were current daily smokers. The majority (81%) who had ever smoked daily began doing so at age 18 years or younger, and 19% began smoking daily at age 19 years or older. Women were as likely as men to report ever having smoked a whole cigarette or ever having smoked daily. Most students (82%) who had ever smoked daily had tried to quit, but 3 in 4 were still smokers. Policies and programs designed to prevent the initiation of smoking and to help smokers quit are needed at both the high school and the college levels to reduce the proportion of young adults who smoke cigarettes.

Results from the 1995 National College Health Risk Behavior Survey.

Results from the 1995 National College Health Risk Behavior Survey, which monitored health risk behaviors among US college and university undergraduates, suggest that many students' behaviors increase their likelihood of adverse health outcomes. During the 30 days preceding the survey, 34% of the participants had consumed five or more alcoholic drinks on at least one occasion, and 27% had drunk alcohol and driven a car. Thirty-one percent had smoked cigarettes regularly during their lifetimes, 49% had ever used marijuana, 30% had used a condom during their last sexual intercourse, 21% were overweight, and 38% had participated in vigorous physical activity on 3 or more of the 7 days preceding the survey. These data were analyzed by gender, age group, race and ethnicity, and institution type. They can be used by those responsible for the health and education of college students to reduce risks associated with the leading causes of mortality and morbidity.