A new set of meta-analyses sheds light on the often complex and conflicting health guidelines linking certain diets, behaviors and conditions to disease. The analyses, conducted by researchers at the Institute for Health Metrics and Evaluation (IHME) at the University of Washington School of Medicine, were published today in Natural medicine. The IHME analyzed the strength of evidence for 180 pairs of risk factors and health outcomes – such as smoking and lung cancer, a diet low in vegetables and type 2 diabetes, high systolic blood pressure and coronary heart disease. Findings are presented in an easy-to-understand star rating system indicating the strength of evidence for each link. The new star rating system aims to help people make personal health decisions, inform health policy and guide future research.
There is extensive research into the relationships between various risks and health outcomes, but the findings are often very different across studies. One of the goals of this new star rating system is to clear up confusion and help consumers make informed decisions about diet, exercise, and other activities that can affect their long-term health.
Dr. Christopher Murray, director of the Institute for Health Metrics and Evaluation and lead author of the study
In many areas, IHME found that the relationship between a risk factor and a health outcome is weaker than some might believe. Nearly two-thirds of the risk-outcome pairs examined—112 of 180—received only one or two stars. These include widely publicized pairings such as a diet high in unprocessed red meat and ischemic stroke (one star). In other cases, the IHME analysis confirmed the widespread consensus. Eight risk-outcome pairs received a five-star rating, including smoking and lung cancer and high systolic blood pressure and ischemic heart disease. A list of star ratings, including a data visualization tool, can be found on the IHME website. Additional star ratings will be added in the near future.
The analysis takes into account both the magnitude of risk shown by studies to date and the consistency of findings between these studies. Star ratings are based on the most conservative interpretation of the available evidence to limit the influence of errors or biases in the underlying data. A one-star rating indicates that there may not be a true relationship between the behavior or condition and the health outcome. Two stars indicate that the behavior or condition is at least associated with a 0-15% change in the probability of a health outcome, while three stars indicate at least a 15-50% change, four stars indicate at least a 50-85% change. and five stars means more than 85% change.
For example, a five-star rating for smoking and lung cancer means that smoking increases the chance of developing or dying from lung cancer by more than 85%. At the other end of the scale, a one-star rating for red meat and ischemic stroke means there may not be a link—in this case, because studies of that link have produced conflicting results.
Notable ratings from the survey include:
“In addition to helping consumers, our analysis can guide policymakers in developing health and wellness education programs so that they focus on the risk factors with the greatest impact on health,” said Dr. Emmanuela Gakidou, professor of health metrics at the Institute for Health Metrics and Evaluation and lead author of the study. “Health researchers can also use this analysis to identify areas where the current evidence is weak and more definitive studies are needed.” The IHME researchers also note that while the meta-analytic approach used by this study does not should replace expert deliberation, it can provide useful input to expert committees and advisory groups that make formal health policy recommendations.
The IHME analysis, which is based on the landmark Global Burden of Disease study, which marks 30 years this year, will be updated regularly. As a result of ever-evolving research, star ratings may change as more data becomes available. This is especially true for pairs with low star counts due to limited or conflicting research. On the other hand, high star ratings are unlikely to change significantly, as the evidence is already compelling.
Institute for Health Metrics and Evaluation
Zheng, P., et al. (2022) Burden of Proof Studies: Assessing the Evidence for Risk. Natural medicine. doi.org/10.1038/s41591-022-01973-2.