Age-related increases in substance use and excess weight-gain that occur among youth are cause for concern as they are associated with numerous negative health outcomes [1–9]. Substance use and obesity (and the correlates of obesity) tend to be established during adolescence [2, 10–12], and most Canadian youth exhibit one or more of these risk factors for future morbidity [10–15]. For instance, according to data from grade 9 to 12 students in the 2008 Youth Smoking Survey (YSS), 8.9% were current smokers (increasing from 6.8% to 15.6% between grade 9 and 12), 18.8% were current marijuana users (increasing from 17.7% to 29.1% between grade 9 and 12), and 27.0% were current binge drinkers (increasing from 21.0% to 50.8% between grade 9 and 12) . Data from the 2007–09 Canadian Health Measures Survey (CHMS) suggest that among Canadian youth aged 15 to 19, 31% of boys and 26% of girls are overweight or obese . In terms of the correlates for obesity, the 2007–09 CHMS identified that only 9% of boys and 4% of girls accumulate 60 minutes of moderate-to-vigorous physical activity (PA) on at least 6 days a week , the 2008 YSS identified that the average daily sedentary screen time among Canadian youth was 7.8 (± 2.3) hours per day , and the 2011 Canadian Community Health Survey (CCHS) identified that only 43.7% of males and 44% of females aged 12 to 19 years consumed five servings of fruits and vegetables daily . It is critical to promote healthier lifestyles among Canadian youth.
While the aforementioned modifiable risk factors for disease are individually important, evidence suggests that having more than one risk factor can act to amplify the risk . Considering that it is common for youth to exhibit more than one of these risk factors [11, 12, 16–20], it is not only important to understand how many Canadian youth are currently failing to meet the Canadian public health guidelines associated with these risk factors [3, 21–26], but it is also important to determine how many youth are at potentially increased risk due to co-occurrence of more than one risk factor. Although some evidence has previously been published on the co-occurrence of modifiable risk factors among youth in Canada using data from the National Longitudinal Survey of Children and Youth (NLSCY) [27–29], that evidence is subject to some major limitations for informing current prevention programming. For instance, although the most recent evidence presented by Alamian and Paradis  are based on longitudinal data, there are four limitations associated with that evidence which warrant new research in this domain: 1) the most recent wave of data examined were from 2004–2005, as such those data are no longer as informative for informing current prevention programming as data from 2010; 2) they examined ever use of tobacco and ever use of alcohol whereas current tobacco or current alcohol use may be more informative, 3) due to changes in guidelines, the measures for tobacco, alcohol use, sedentary behaviour and PA were not operationally defined according to definitions within the current prevention guidelines; and 4) the according to Statistics Canada , the NLSCY was only nationally representative to the original sample population (Cycle 1). Although these earlier reports are important [27–29], additional investigation into this issue is warranted with the most current nationally representative youth data available.
Considering schools provide an effective environment for intervening with youth , and international guidelines recommend a comprehensive approach to achieving health promoting schools [32, 33], the objective of this study is to use nationally representative data collected from grade 9 to 12 students to determine the prevalence for the these major modifiable risk factors for disease and examine how prevalence rates and co-occurence of risk factors change across grades.