Interacting and joint effects of atherogenic index of plasma and dietary inflammatory index on hypertension-diabetes comorbidity risk in Chinese elderly adults: results from China Nutrition and Health Surveillance in 2015–2017

Objective This study aimed to investigate the interaction and joint effects of the atherogenic index of plasma (AIP) and dietary inflammatory index (DII) on hypertension-diabetes comorbidity (HDC) among Chinese elderly adults. Methods The study data were derived from the 2015–2017 China Nutrition and Health Surveillance. Participants were categorized by AIP tertiles (T1, T2, T3) and DII score (<0, ≥0). Logistic regression models were used to analyze the independent associations, interactions, and joint effects of AIP and DII on HDC. Results A total of 18,447 elderly participants were included, with a median age of 66.32 (IQR: 62.86, 71.56) years and including 9,650 (52.31%) males. The median AIP was −0.04 (IQR: −0.24, 0.17), and the median DII score was 1.63 (IQR: −0.13, 2.85). After adjusting for confounders, compared with the T1 group of AIP, the risk of HDC increased by 0.37-fold (OR = 1.37, 95% CI: 1.14–1.65, p = 0.001) in the T2 group and by 1.30-fold (OR = 2.30, 95% CI: 1.93–2.74, p < 0.001) in the T3 group; compared with the anti-inflammatory diet group (DII < 0), the risk of HDC increased by 0.19-fold (OR = 1.19, 95% CI: 1.03–1.38, p = 0.019) in the pro-inflammatory diet group (DII ≥ 0). No significant multiplicative (OR = 0.94, 95% CI: 0.63–1.40) and additive (relative excess risk due to interaction = 0.25, 95% CI: −0.37 − 0.87) interactions were found between AIP and DII on the risk of HDC. Results of the joint effect analysis showed that, compared with the group with an anti-inflammatory diet and lower AIP, the group with a pro-inflammatory diet and higher AIP had a 1.98-fold (OR = 2.98, 95% CI: 2.16–4.13, p < 0.001) increased risk of HDC. Conclusion Higher AIP levels and a pro-inflammatory diet were both associated with an increased risk of hypertension-diabetes comorbidity in Chinese elderly adults. Although the multiplicative and additive interactions between AIP and DII on HDC risk were not statistically significant, joint effect analysis revealed that individuals with both high AIP and a pro-inflammatory diet had a significantly higher HDC risk compared to those with only a single risk factor.