The impact of body mass index on health service utilization among pilgrims: a comprehensive analysis.

BACKGROUND: Body Mass Index (BMI), a measure based on weight and height, is a key indicator for assessing health status and the risk of chronic diseases such as hypertension, diabetes, and cancer. Both ends of the BMI distribution have been associated with greater healthcare utilization, with prior evidence in general populations suggesting a non-linear (U-shaped) association in which underweight and obese individuals use more healthcare services than those with normal weight. This relationship is particularly important during mass gatherings like the Hajj pilgrimage, where overcrowding, extreme heat, and physical exertion can amplify health risks. This study aimed to investigate how variations in BMI influence clinic visits, hospital stays, and diagnoses among pilgrims during Hajj. METHODS: A cross-sectional study was conducted among 4,000 pilgrims randomly selected from the official Hajj registry during the 2024 (1445 H) season. BMI was modelled as a categorical variable (<18.5, 18.5-24.9, 25-29.9, and ≥30 kg/m²), with the normal-weight category as the reference, allowing detection of non-linear (U-shaped) associations. Outcomes were clinic visit (yes/no), hospital admission (yes/no), and primary diagnosis, all collected using a standardized data collection form. Crude and adjusted odds ratios (cOR, aOR) with 95% confidence intervals and exact p-values were estimated using multiple logistic regression, adjusting simultaneously for age, gender, education, WHO region, marital status, employment, and smoking. RESULTS: Underweight (BMI <18.5) and obese (BMI ≥30) pilgrims reported higher rates of clinic visits (9% and 10%, respectively) and higher rates of hospital admission than normal-weight and overweight pilgrims, confirming a U-shaped association between BMI and healthcare utilization. The most frequent diagnoses were heat-related illnesses (75% of admissions among underweight, 76% among obese), followed by chronic-disease follow-up, particularly at BMI extremes. In the adjusted analyses, WHO region and employment status remained significantly associated with clinic visits, with lower odds among pilgrims from South-East Asia and higher odds among unemployed individuals with BMI <18.5. CONCLUSION: Both low and high BMI are linked to greater healthcare utilization during Hajj. Implementing targeted risk assessments, pre-travel health education, and culturally adapted healthcare services for BMI extremes may reduce acute healthcare demand during mass gatherings.