With the explosive growth of medical information, it is almost impossible for healthcare providers to review and evaluate all relevant evidence to make the best clinical decisions. Meta‐analyses, which summarize all existing evidence and quantitatively synthesize individual studies, have become the best available evidence for informing clinical practice. This article introduces the common methods, steps, principles, strengths and limitations of meta‐analyses and aims to help healthcare providers and researchers obtain a basic understanding of meta‐analyses in clinical practice and research.

Evidence for the effects of dietary diversity changes and cognitive frailty (CF) in the older adults is not clear. This study aimed to investigate the relationship between dietary diversity changes and CF in older adults Chinese. A total of 14,382 participants (mean age: 82.3 years) were enrolled. Dietary diversity scores (DDSs) were collected and calculated using a food frequency questionnaire. DDS changes between baseline and first follow-up were categorized into nine patterns. The associations between DDS changes and the incidence of CF were estimated using Cox proportional hazards models. During an 80,860 person-year follow-up, 3023 CF cases were identified. Groups with a decrease in DDS had increased CF risk compared with the high-to-high DDS group, with adjusted hazard ratios (HRs; 95% confidence intervals (Cis)) of 1.30 (1.06, 1.59), 2.04 (1.51, 2.74), and 1.81 (1.47, 2.22) for high-to-medium, high-to-low, and medium-to-low groups, respectively. Lower overall DDS groups were associated with greater CF risks, with HRs (95% CIs) of 1.49 (1.19, 1.86) for the low-to-medium group and 1.96 (1.53, 2.52) for the low-to-low group. Compared with the high-to-high group, significant associations with CF were found in other DDS change groups; HRs ranged from 1.38 to 3.12 for the plant-based DDS group and from 1.24 to 1.32 for the animal-based DDS group. Additionally, extreme and moderate declines in overall DDS increased CF risk compared with stable DDS, with HRs (95% CIs) of 1.67 (1.50, 1.86) and 1.13 (1.03, 1.24), respectively. In conclusion, among older adults, a declining or persistently low DDS and a moderately or extremely declining DDS were linked to higher incident CF. Plant-based DDS changes correlated more strongly with CF than animal-based DDS changes.

Background Insomnia symptoms are prevalent in older adults and linked to cardiovascular disease (CVD), but the role of long-term symptom trajectories remains unclear. We investigated associations between insomnia symptoms, their trajectories over time and incident CVD in a population-based cohort. Methods This longitudinal study included 12 102 participants aged ≥50 years without baseline CVD from the US Health and Retirement Study (2002–2018). Insomnia symptoms (non-restorative sleep, difficulty initiating/maintaining sleep, early awakening) were assessed at baseline; trajectories were modelled over 4 years (2002–2006) using latent class analysis. Cox models estimated HRs for incident CVD (heart disease or stroke), adjusted for sociodemographics, lifestyle and comorbidities. Results During a median of 10.2-year follow-up, 3962 incident CVD events occurred. Compared with no symptoms, participants with one, two, or three to four symptoms had higher CVD risk (HR 1.16, 95% CI 1.05 to 1.27; HR 1.16, 95% CI 1.05 to 1.28; HR 1.26, 95% CI 1.15 to 1.38, respectively). Four trajectories were identified: persistent low (56.3%), decreasing (27.1%), increasing (7.2%) and persistent high (9.5%). Compared with persistent low, increasing (HR 1.28, 95% CI 1.10 to 1.50) and persistent high (HR 1.32, 95% CI 1.15 to 1.50) trajectories were associated with elevated CVD risk. Conclusions Greater burden of insomnia symptoms at baseline and trajectories over time were associated with higher CVD incidence in older adults.

Short-term exposure to air pollutants increases the risk of migraine, but the long-term impacts of exposure to multiple pollutants on migraine have not been established. The aim of this large prospective cohort study was to explore these links. A total of 458,664 participants who were free of migraine at baseline from the UK Biobank were studied. Cox proportional hazards models were used to estimate the risk of new-onset migraine from combined long-term exposure to four pollutants, quantified as an air pollution score using principal component analysis. During a median (IQR) follow-up of 12.5 (11.8, 13.2) years, a total of 5417 new-onset migraine cases were documented. Long-term exposure to multiple air pollutants was associated with an increased risk of new-onset migraine, as indicated by an increased in the SDs of PM_2.5 (hazard ratio (HR): 1.04, 95% CI: 1.01-1.06, P = 0.009), PM₁₀ (HR: 1.07, 95% CI: 1.04-1.10, P < 0.001), NO₂ (HR: 1.10, 95% CI: 1.07-1.13, P < 0.001) and NOx (HR: 1.04, 95% CI: 1.01-1.07, P = 0.005) in the main model. The air pollution score showed a doseresponse association with an increased risk of new-onset migraine. Similarly, compared with those of the lowest tertile, the HRs (95% CI) of new-onset migraine were 1.11 (95% CI: 1.04-1.19, P = 0.002) and 1.17 (95% CI: 1.09-1.26, P < 0.001) in tertiles 2 and 3, respectively, according to the main model (P trend < 0.001). Long-term individual and joint exposure to multiple air pollutants is associated with an increased risk of new-onset migraine.

Aims: This study aimed to explore the associations of exposure to residential green space and natural environment with incident heart failure (HF) risk and to investigate the role of PM2.5 and physical activity in these associations. Methods and results: We conducted a prospective study using data from the UK Biobank cohort, which included 437 656 participants. Cox proportional hazards regression models were employed to assess the association between residential exposure and HF risk, adjusting for multiple potential confounding factors. Casual mediation analysis was used to determine the mediation effect of PM2.5 and physical activity. Over a median follow-up of 13.5 years, 16 209 cases with HF were recorded. In the fully adjusted models, participants with green space coverage and natural environment coverage at the 300 m buffer in the highest tertiles had 13% [hazard ratio (HR) = 0.87, 95% confidence interval (CI): 0.84–0.91] and 12% (HR = 0.88, 95% CI: 0.84–0.91) lower risks of incident HF, respectively. Similar protective associations were observed for green space (HR = 0.87, 95% CI: 0.84–0.91) and the natural environment (HR = 0.85, 95% CI: 0.81–0.88) at the 1000 m buffer. PM2.5 and physical activity partially mediated these relationships between residential exposure and HF risk. Conclusion: Increased residential green space and natural environment levels were associated with decreased risk of incident HF, and these associations may be partially mediated by PM2.5 and physical activity.