**Background:** Health-compromising behaviours (e.g., tobacco use, excessive alcohol, physical inactivity, unhealthy diet) and oral health-compromising behaviours (e.g., poor oral hygiene) are known risk factors for non-communicable diseases (NCDs) and negatively impact military combat readiness. These behaviours often co-occur or cluster together, yet no prior study had examined clustering of health- and oral health-compromising behaviours (HOHCBs) in Malaysian adults or military personnel. This study aimed to identify clustering patterns and assess the clustering number of HOHCBs in army personnel in Central Peninsular Malaysia.
**Methods:** A cross-sectional study was conducted using a validated online self-administered questionnaire covering 10 health behaviour domains (33 items: medical visits, physical activity, sedentary lifestyle, dietary intake, smoking, alcohol consumption, drug/substance abuse, sleep, aggressive behaviour, road safety) and 5 oral health behaviour domains (9 items: toothbrushing, fluoridated toothpaste, flossing, dental visits, bruxism). A multistage sampling method (stratified, proportionate, simple random sampling) was employed. The required sample size was 1,800; 2,435 respondents participated (100% completion rate after mean imputation for missing values). Hierarchical agglomerative cluster analysis (HACA) with between-groups linkage and squared Euclidean distance was used, validated by repeated HACA on sub-samples and K-means cluster analysis.
**Key Results:** The mean age of respondents was 30.3 years (SD=5.9); 92.5% were male, 77.0% Malay, 67.5% married, 87.4% educated to secondary school level, and 83.9% had no medical conditions. HACA revealed two broad clusters: Cluster 1 ('unhealthy lifestyles with high-risk behaviours') comprised 30 HOHCBs including high consumption of carbonated/acidic/sweet foods and drinks, extended sitting/lying, drug use, physical inactivity, non-fluoridated toothpaste, poor toothbrushing, alcohol consumption, not wearing helmets/seatbelts, aggressive behaviour, bruxism, symptomatic dental visits, high fatty-food consumption, and extended screen time. Cluster 2 ('most common risk behaviours') comprised 12 HOHCBs including unrecommended consumption of vegetables, fruits, cereals, milk/dairy, and poultry/fish/meat/legumes; low plain-water intake; smoking and tobacco exposure; texting/calling while driving; and infrequent flossing. K-means cluster analysis confirmed two clusters: Cluster 1 contained 50.3% of respondents (n=1,224) with 17 HOHCBs; Cluster 2 contained 49.7% (n=1,211) with 9 HOHCBs. The clustering number ranged from 0 to 29 HOHCBs per individual, with a mean of 14.1 (SD=4.1). The most common clustering number was 15 (9.2% of respondents), followed by 13 (9.0%), 16 (8.7%), and 14 (8.7%).
**Clinical Implications:** The finding that army personnel engage in an average of 14.1 HOHCBs simultaneously is alarming and has direct implications for health readiness and combat readiness. The two identified clusters provide a framework for targeted, multi-behaviour health promotion using the common risk factor approach. With limited resources, policymakers should prioritise Cluster 2 ('most common risk behaviours') as it contains the most prevalent HOHCBs, followed by Cluster 1 ('high-risk behaviours'). Within these clusters, individuals with higher clustering numbers should be prioritised. Interventions addressing multiple behaviours simultaneously (e.g., nutrition, smoking cessation, road safety, oral hygiene) are likely to have greater public health impact than single-behaviour programmes. Limitations include reliance on self-reported data (potential under-/over-reporting of sensitive behaviours like substance abuse) and restriction to army personnel in Central Peninsular Malaysia (excluding navy, air force, and other army formations).