Results
The study included 1,683 middle-aged and elderly participants aged 40 and older, including 740 males and 943 females. According to the Shapiro–Wilk normality test, the PA level for each group conformed to a non-normal distribution ( P < 0.05). Approximately 9.3% of the participants reported not engaging in regular exercise, with a slightly higher percentage of females than males falling into this category. No significant difference in the weekly PA level among middle-aged and elderly individuals was observed between different genders ( P > 0.05). About 51.8% of the participants in this study had at least one chronic disease, and Kruskal–Wallis test showed no significant difference in weekly PA levels between participants with different numbers of chronic diseases ( P > 0.05). The proportion of participants not exercising was higher among those aged 40–59 than among those aged 60–69 and ≥70 years. There was a statistically significant difference in weekly PA levels across different age groups ( P < 0.001), with participants aged 60–69 and ≥70 years showing significantly higher PA levels than those aged 40–59 years ( P < 0.001). Brisk walking was identified as the preferred form of physical exercise for individuals over 40. Significant differences were observed in weekly PA levels among middle-aged and elderly participants from different regions ( P < 0.001), with those in the eastern and central regions engaging in higher levels of PA compared to those in western China ( P < 0.001). All data are shown in Table 1 and Figure 2 .

Notes:

As shown in Table 2 , there was a statistically significant difference in the frequency of colds experienced by middle-aged and elderly individuals with varying levels of weekly PA ( P < 0.001). However, no significant differences were found in cold frequency between participants of different sexes or age groups ( P > 0.05). The frequency of colds in the past year was significantly different among middle-aged and elderly individuals with various chronic diseases ( P = 0.0011). Additionally, there was a statistically significant variation in the risk of colds among middle-aged and elderly individuals residing in different regions ( P < 0.001).

Table 3 presents the results of the logistic regression analysis regarding the frequency of colds among participants. The participants had a lower risk of getting a cold if they exercised at moderate (OR = 0.64, P < 0.001, 95% confidence interval (CI) [0.50∼0.81]) and high levels of PA (OR = 0.64, P < 0.001, 95% CI [0.51∼0.79]) per week than if they exercised at low levels of PA. Participants with single chronic diseases (OR = 1.47, P < 0.001, 95% CI [1.20∼1.80]) and multiple chronic diseases (OR = 1.56, P < 0.001, 95% CI [1.21∼2.00]) were at higher risk of catching a cold than participants without chronic diseases. Middle-aged and elderly people living in central (OR = 1.64, P < 0.001, 95% CI [1.33∼2.01]) and western China (OR = 1.49, P = 0.008, 95% CI [1.11∼2.00]) are at higher risk of catching a cold than those in the eastern China.

Participants’ weekly PA was included as a continuous variable in a restricted cubic spline model. The data were processed by selecting four nodes (P5, P25, P75, P95) based on percentile and after adjusting for confounders such as gender, age, chronic disease prevalence, and region. The analysis revealed a linear dose–response relationship between PA and the frequency of colds experienced (Nonlinear test results: 1 time, χ 2 = 3.85, P = 0.146; ≥2 times, χ 2 = 2.51, P = 0.285).

Figure 3A presents a schematic of the dose–response relationship between weekly PA level and having a cold once in the past year. When OR = 1 corresponds to a PA level of 537.29 MET-min/wk, meaning that individuals who have had one cold in the past year should engage in PA of at least 537.29 MET-min/wk per week to reduce their risk of having another cold. Figure 3B presents a schematic of the dose–response relationship between weekly PA level and having two or more times in the past year. When OR = 1 corresponds to a PA level of 537.76 MET-min/wk, meaning that individuals who have had two or more colds in the past year should engage in PA level of at least 537.76 MET-min/wk per week to reduce their risk of having another cold. In summary, for the adults participating in this research, increasing their weekly PA level to 538 MET-min/wk could significantly reduce the risk of getting a cold.