Abstract
Polyphenols are secondary metabolites found in plants, foods, and drinks, occurring in small quantities and showcasing antioxidant and anti-inflammatory qualities. The primary polyphenols consist of flavonoids, phenolic acids, stilbenes, and lignans. However, there is currently no comprehensive quantitative analysis of epidemiological data on overall death rates. This systematic review with meta-analysis aims to identify the exposure-response relationship between dietary polyphenol intake and all-cause mortality. The literature was reviewed from its earliest study to May 2024, utilizing six distinct electronic databases. No specific criteria were used to choose participants based on the recruiting environment, their general health condition, country, or ethnicity. The inclusion criteria for studies were as follows: a longitudinal design, exposure to dietary polyphenols, all-cause mortality as the outcome, and hazard risk (HR) as the impact measure. The Newcastle-Ottawa Scale was used to evaluate the methodological rigor of the study. The hazard risks (HRs) and 95% confidence intervals (CIs) were estimated by pooling data using common effects models. A protocol has been registered on PROSPERO with the identification number CRD42024545524. The meta-analysis comprised seven cohort studies that involved 178,657 adult people aged 18 years and older. These studies examined the relationship between total dietary polyphenol consumption and the risk of all-cause death. The recruitment settings exclusively used community-based approaches, with a preference for Europe (71%) in terms of geographic distribution. The study’s quality was assessed to be moderate to high. The meta-analysis showed consistent evidence that increased dietary exposure to polyphenols reduces the risk of all-cause mortality by 7% (HR 0.93, 95% CI 0.91–0.95, I2: 48%). Pooled data from the available evidence consistently show that individuals exposed to an antioxidant diet rich in polyphenol sources may be at lower risk of all-cause mortality.
Generated Summary
This systematic review and meta-analysis aimed to identify the exposure-response relationship between dietary polyphenol intake and all-cause mortality. The literature was reviewed from its earliest study to May 2024, utilizing six distinct electronic databases. The meta-analysis comprised seven cohort studies that involved 178,657 adult people aged 18 years and older. The studies examined the relationship between total dietary polyphenol consumption and the risk of all-cause death. The Newcastle-Ottawa Scale was used to evaluate the methodological rigor of the study. The hazard risks (HRs) and 95% confidence intervals (CIs) were estimated by pooling data using common effects models. A protocol has been registered on PROSPERO with the identification number CRD42024545524. The recruitment settings exclusively used community-based approaches, with a preference for Europe (71%) in terms of geographic distribution.
Key Findings & Statistics
- The meta-analysis comprised seven cohort studies.
- The studies involved 178,657 adult people aged 18 years and older.
- The average follow-up period was 4 years, ranging from 5 to 12 years.
- The recruitment settings were all community-based.
- Europe (71%) was the predominant geographic distribution.
- The meta-analysis showed consistent evidence that increased dietary exposure to polyphenols reduces the risk of all-cause mortality by 7% (HR 0.93, 95% CI 0.91–0.95, I2: 48%).
- Castañeda J, 2024: HR 0.87 [0.76; 0.99], Weight 2.4%
- María Mérida D, 2023: HR 0.84 [0.68; 1.03], Weight 1.0%
- Taguchi C, 2020: HR 0.90 [0.82; 0.99], Weight 4.6%
- Pounis G, 2018: HR 0.78 [0.62; 0.97], Weight 0.8%
- Tresserra-Rimbau A, 2014: HR 0.63 [0.41; 0.97], Weight 0.2%
- Zamora-Ros R, 2013: HR 0.70 [0.49; 0.99], Weight 0.3%
- Talavera-Rodriguez I, 2023: HR 0.94 [0.92; 0.96], Weight 90.7%
- Common effect model: HR 0.93 [0.91; 0.95], 100.0%
Other Important Findings
- The study found that higher dietary exposure to polyphenols reduces the risk of all-cause mortality.
- The results of the sensitivity analysis showed that, after excluding each study at a time, higher daily dietary polyphenol consumption was still largely associated with a significant reduction in all-cause mortality risk, indicating that the results of the meta-analysis are robust.
- The quality assessment of the seven studies according to the NOS showed an average high level of quality.
- The main strength of the study is the inclusion of prospective cohort studies and a large number of participants and deaths, providing greater statistical power to quantitatively assess the association between dietary polyphenol consumption and all-cause mortality.
Limitations Noted in the Document
- The reported associations may be influenced by residual or unmeasured confounding factors, although many covariates were considered.
- The use of FFQ to assess daily dietary intake, although a common and validated method in epidemiological research, suffers from a reporting bias related to self-perceived intakes.
- The observational nature of the included studies may influence the reported associations.
Conclusion
The findings consistently show that individuals exposed to an antioxidant diet rich in polyphenol sources may be at a lower risk of all-cause mortality. The meta-analysis indicates a robust association between higher dietary polyphenol intake and a reduced risk of all-cause mortality, with a 7% reduction in mortality risk. The study highlights the importance of considering total dietary polyphenol intake in relation to overall health outcomes. Further research should focus on specific subclasses of polyphenols to better understand their individual impact. The findings support the hypothesis that increased intake of polyphenols and their subclasses may extend longevity through multifactorial pathways. The relationship between oxidative stress and inflammation is well-established, and both processes are linked to the development of non-communicable diseases and reduced survival, hence why polyphenols act sufficiently in counteracting mortality trajectories.