Background Multimorbidity imposes a heavy burden on individuals, families, and society. There are relatively few studies exploring patterns of multimorbidity among middle-aged adults in China.

Objective To explore the current status of multimorbidity, associated risk factors, and multimorbidity patterns among adults aged 45-64 years in China, so as to provide a scientific basis to prevent and control multimorbidity in China.

Methods A total of 5494 adults aged 45-64 years from the Chinese Health and Nutrition Survey (CHNS) in 2018 were selected. Of these, 2494 (45.39%) were men and 3000 (54.61%) were women. The nine diseases included were hypertension, diabetes, dyslipidaemia, obesity, mild cognitive impairment (MCI), myocardial infarction, stroke, asthma, and tumor. The prevalence of each disease or multimorbidity was expressed as N (%). Comparisons of multimorbidity prevalence between different groups were performed using the χ² test or Cochran-Armitage trend test. Association rule with the Apriori algorithm was used to explore the pattern of multimorbidity, with parameters set at a minimum conditional support of 3.00%, a minimum rule confidence of 50.00%, and a lift of >1.20. Logistic regression was used to evaluate the associations between selected risk factors and multimorbidity.

Results In 2018, 37.44% of participants reported multimorbidity in 15 provinces of China. The prevalence of diseases in descending order was dyslipidaemia (39.99%), hypertension (39.48%), obesity (16.42%), MCI (14.47%), diabetes (14.16%), tumor (1.09%), stroke (1.04%), myocardial infarction (0.71%), and asthma (0.64%). A total of seven multimorbidity patterns were identified in this group. Obesity paired with hypertension, and diabetes paired with dyslipidemia were the two major patterns of multimorbidity in the general population and age or sex subgroups. The multimorbidity patterns of different populations were concentrated in the combination of obesity, hypertension, diabetes, and dyslipidemia. The risk of multimorbidity was lower in females than in males (OR=0.85, 95%CI: 0.75, 0.97). The multimorbidity risk was 1.56 times higher in the 55-64 years group than in the 45-54 years group (OR=1.56, 95%CI: 1.40, 1.75). Drinking in the past year increased the risk of multimorbidity by 25% (OR=1.25, 95%CI: 1.08, 1.45) compared to no alcohol comsumption in the past year. High and medium levels of physical activity were associated with a decreased OR (high: OR=0.74, 95%CI: 0.65, 0.85; medium: OR=0.81, 95%CI: 0.70, 0.93) with low level of physical activity as reference.

Conclusion In 2018, there was a high prevalence rate of multimorbidity among middle-aged adults in China. The main multimorbidity patterns were obesity-hypertension and diabetes-dyslipidemia. Surveillance and interventions should be strengthened particularly for men, individuals with alcohol consumption or insufficient physical activity, and those with major multimorbidity patterns.