Background:
Non Communicable Diseases (NCDs) are majorly associated with four common health compromising behaviours - tobacco use, physical inactivity, unhealthy diet and harmful use of alcohol. These health compromising behaviours do not occur in isolation and often tend to co-occur as clusters. The aim of this study was to explore the prevalence and clustering of four behavioural risk factors for NCDs among adolescents and to assess if socioeconomic inequalities exist in these clustering patterns.

Methods:
A cross sectional study was undertaken among 1,085 adolescents (15-19 year old) in the city of New Delhi, India. An interviewer administered questionnaire was used to assess health compromising behaviours (tobacco use, alcohol use, unhealthy diet and physical inactivity), and socio-demographic data. Clustering was assessed using pairwise correlations, counts of clustering of health compromising behaviours and comparison of observed/ expected ratios. Multivariable logistic regressions were used to assess the relationship between variations in clustering by self-reported wealth and education of adolescents.

Results:
Two major clusters of health behaviours emerged; tobacco and alcohol use and tobacco and unhealthy diet, with tobacco use emerging as a gateway health compromising behaviour. Pronounced clustering of health compromising behaviours were observed with lower levels of education and wealth. In the multi-variable regression models, the crude estimates showed that poorer adolescents were at 2.6 times (95% CI 1.6, 4.2) and 3.4 times (95% CI 1.9, 6.2) higher odds of having the clustering between tobacco and alcohol and tobacco and unhealthy diet respectively in comparison to richer adolescents.

Conclusions:
Tobacco use was the gateway risk behaviour which significantly clustered with other NCD risk behaviours. Clustering of health behaviours was socio-economically patterned. Area of residence and age modified the associations between clustering of behaviours and socio-economic position. Targeting interventions to promote positive health behaviours especially for tobacco control amongst adolescents should be a key public health priority.