Adolescence is a critical developmental period in the lifespan during which social and psychological norms are established and significant physical and emotional changes take place (Murray et al., 2011). To cope with these changes, many adolescents engage in risky behaviors (Richter, 2010), eventually leading to established behavioral patterns for some. In addition, other factors like genetic, environmental and intra-/interpersonal factors are associated with engaging in risky behaviors. Unhealthy behavior among adolescents represents an important public health problem with both long- and short-term effects. Early adoption and continued use of legal and illegal drugs, for example, may lead to lifelong dependency and negative health consequences as an adult (DeWit et al., 2000). Moreover, individuals who consume alcohol at an early age are more likely to experience employment problems and show criminal or violent behavior in later life compared with those who do not (Ellickson et al., 2003). In the short-term, risky behaviors such as under-age alcohol consumption have been associated with increased risk for bodily injury from traffic-related accidents (Beck et al., 2010).
Several theories help explain the development and nature of health-related risk behaviors in adolescence. The Deterrence Hypothesis, for example, focuses specifically on the association between risk behavior and sports. It proposes that participation in sports moderates delinquent behavior (Eitle et al., 2003; Leonard, 1995; Schafer, 1969) through exposures that promote conforming to rather than deviation from social norms (Begg et al., 1996). In organized sports, for example, adolescents are provided with structured time schedules, supervision and frequent exposure to normative behaviors associated with health benefits (Begg et al., 1996; Eitle et al., 2003). An expanded social network resulting from newly developed friendships may also promote development of group identities and cultures (Eccles et al., 2003) and sharing strategies for coping with daily problems (Sygusch, 2005) that also benefit health status. Some have proposed, therefore, that participation in sports may be protective against drug use (Lisha and Sussman, 2010).
Pressures that prompt young athletes to refrain from engaging in risky behaviors exist alongside those that promote unhealthy behavior, however. The Athletic Delinquent Hypothesis, for example, supports the notion that health-related risk behaviors may result from participation in sports activities (Begg et al., 1996). Due to a multitude of obligations, athletes are exposed to numerous pressures (Heyman, 1986). According to a literature review on athletic participation in high school and college, higher alcohol consumption was prevalent among athletes (Lisha and Sussman, 2010). This may have resulted from a sense of competition, stress resulting from frequent testing and performance evaluation, perceived norms based on assumptions that other athletes consume alcohol at high levels, and frequent exposure to commercials for alcohol products during sports events (Lisha and Sussman, 2010).
While previous work provides insight into patterns of health behaviors among older adolescent athletes (Martens et al., 2006), their focus has been in specific areas: eating disorders (Forsberg and Lock, 2006; Gabel, 2006; Hildebrandt, 2005), use of performance-enhancing nutritional supplements (Lawrence and Kirby, 2002), the female athlete triad (a syndrome consisting of eating disorders, amenorrhea, and osteoporosis) (Golden, 2002), and the use of alcohol and drugs (Martens et al., 2007). Comprehensive and critical summaries on more common risky behaviors are less evident, especially for individuals 18 years and younger, an age considered to represent the main period of adolescence (Blos, 1962, 1979). Specific focus on these issues in this younger age group is important because risky behaviors can have immediate negative consequences on physical performance (e.g., bronchospasm in adolescent smokers) and social functioning (American College of Sports Medicine, 2007; Foulds et al., 2008; Leon et al., 1981). Although useful, two earlier reviews of risk behaviors in adolescent athletes (Lisha and Sussman, 2010; Mays et al., 2011) have important limitations: the former focused primarily on alcohol, tobacco and illicit drug use among high school and college athletes, while the latter was restricted to alcohol consumption in U.S. athletes. Although neither review addressed important issues such as eating and doping behaviors, both recommended the need for additional research especially on adolescent athletes across a broader age range and more diverse geographic settings and on common behaviors such as tobacco use (Lisha and Sussman, 2010).
If clear patterns of risky behavior exist for the main period of adolescence, their recognition would guide the development of programs for preventing or reducing health effects in adolescence and later in life. The purpose of this report, therefore, was to systematically examine international literature to identify the frequency of risk behaviors (i.e. use of alcohol, tobacco, drugs, performance enhancing drugs and nutrition) among younger adolescents being low and high-involved in sports.
Procedures used in this literature review follow the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) Statement (Moher et al., 2009), a more recent revision of the QUOROM (Quality of Reporting of Meta-analyses) Statement (Moher et al., 1999). To assess health behaviors of young adolescent athletes from multiple disciplinary perspectives, we chose PubMed, CSA Sociological Abstracts and PsycINFO as the medical, sociological and psychological databases, respectively, for the literature search. Search terms were based on the Medical Subject Heading (MeSH) system. Altogether, there were twelve search combinations performed in each database. The words "adolescent" and "athlete OR sports" built the base for each combination and were in each case accompanied by the following words: "alcohol", "smoking", "cannabis OR marihuana", "eating behavior OR nutrition", "health behavior", or "doping" .
Studies were selected if they contained one or more of the above-mentioned search terms in the title or abstract, represented original articles published in a peer-reviewed journal in English, reported quantitative results and appeared in printed or electronic form between January 1st, 1990 and December 31st, 2010. Given a focus on younger athletes in the main period of their adolescence (Blos, 1962; 1979), we included studies in which the maximum age of participants was 18 years or the sample mean age was less than 19 years. With this approach, it was possible to identify a wide range of studies including adolescents aged 18 years and younger. Articles focusing on specific configurations of behavior and disease, such as the female athlete triad (a syndrome consisting of eating disorders, amenorrhoea, and osteoporosis), were excluded. Additionally, we excluded reviews, case studies, book chapters, dissertations and essays in large part because comprehensive and consistent identification of these forms of "grey literature" is not possible through currently available electronic databases of scientific literature. Attempts to incorporate information of this sort would therefore have yielded a pool of studies with results that could not be reliably replicated by others. Secondly, a focus on original papers published in peer-review journals has the potential additional benefit of ensuring more uniform quality and reduced study heterogeneity.
The search took place on May 25th, 2011 and produced 2,159 hits (Pubmed 1,577 hits; CSA 296 hits; and PsycINFO 286 hits). After discarding duplicate publications of the same study, 2,057 articles remained (see Figure 1). Following review of references cited in each, seven additional articles were identified.
We reduced the pool of 2,064 potentially eligible articles to 97 following abstract review and to 78 upon detailed review of each manuscript. This two-step selection process (Figure 1) was conducted independently by the first (KD) and last (SvS) authors. After each step, decisions on eligibility were compared. Cohen's Kappa for inter-rater-reliability at this stage was 0.72 for the first selection step and 0.94 for the second (Cohen, 1960). In the few cases in which differences were noted, each was discussed and a final determination was made by the first author (KD).
Each article in the final analytic sample was evaluated using a standardized form. Outcomes of interest included the frequency of common health-related behaviors (i.e., consumption of alcohol, tobacco products, illicit drug use, eating behaviors, and doping) and the level at which adolescents participated in sports (e.g., high-involved athletes, low-involved athletes). Data on comparison groups (e.g., high-involved athletes vs. low-involved athletes; low-involved athletes vs. those not involved in sports [non-athletes]) were used for comparison when available. Our assessment also took note of several methodological aspects of each report including its study design, characterization of the groups targeted for study and the way in which risky behaviors were operationally defined and measured. Because our assessment revealed considerable heterogeneity across studies in nearly all study features and because the number of articles addressing specific risk behaviors was small, the current report primarily provides descriptive statistics. In instances in which three or more studies used the same definition of a risk behavior, subgroup meta-analyses were performed to summarize prevalences. The I squared statistic is reported for each summary measure of prevalence or association as an indicator of study heterogeneity. Since all analyses showed a high [I.sup.2], we used random effects models. Additionally,...