Study: Top health risks are air pollution and high blood pressure

A recent study published in The Lancet estimates relative health risks, exposure levels, and disease burden in the Global Burden of Disease, Injuries, and Risk Factors study. (GBD) for 2021

The COVID-19 pandemic has highlighted significant health disparities at the individual and geographic levels due to multiple risk factors and differences in health care systems around the world.

Carefully conducted meta-analyses of risk factors can inform public policy about emerging or ongoing health problems, as well as identify notable areas of public health progress. To generate data for these analyses, GBD estimates relative health risks by exposure level, risk factor exposure, and disease burden attributable to multiple risk factors.

Several other research networks, such as the NCD Risk Factor Collaboration (NCD-RisC), have provided valuable population-level and multi-country data on specific risk factors. However, only the GBD systematically analyzes multiple risk factors in 204 countries and territories around the world. For example, between 1990 and 2021, GBD analyzed 88 risk factors in 204 countries and 811 subnational locations.

The current study summarizes the methods adopted in GBD 2021. It provides estimates of exposure levels to 88 risk factors and their combinations, and the relationship of these risk factors to health outcomes. Data were obtained from 54,561 different sources to create epidemiological estimates, with estimates obtained for 631 risk factor-outcome pairs.

The association between risk factor and outcome was data-driven, and sex-, age-, location-, and year-specific estimates were calculated at regional, national, and global levels. For a given risk factor, the relative risks (RR) of a specific outcome were estimated.

Summary exposure values (SEVs) measured risk-adjusted exposure prevalence. In addition, theoretical minimum risk exposure levels (TMRELs) were used for each risk factor to calculate the population attributable fraction (PAF). Risk factor burden was the product of PAF and disease burden expressed in disability-adjusted life years (DALYs).

Particulate matter air pollution has been identified as a major contributor to the global burden of disease in 2021, accounting for 8% of total DALYs. The next key contribution was high systolic blood pressure (SBP), which accounted for 7.8% of total DALYs. Smoking, low birth weight, short gestation, and high fasting plasma glucose (FPG) contributed 5.7%, 5.6%, and 5.4% of total DALYs, respectively.

For infants and children under 14 years of age, the main risk factors were unsafe water, low birth weight, short gestation, hand washing and sanitation. For older cohorts, key risk factors were high body mass index (BMI), FPG, SBP and low-density lipoprotein (LDL) cholesterol levels.

Between 2000 and 2021 there has been a marked shift in global health issues. During this period, the reduction in all age-specific DALYs can be explained by a 20.7% reduction in behavioral risks and a 22% reduction in environmental and occupational risks. This was accompanied by an almost 50% increase in DALYs caused by high metabolic risks.

The current study identified several risk factors for which sufficient measures have not been taken. Linking disease burden to risk factors is important as it can help with prioritization when resources are limited.

The main limitation of the 2021 GBD was the exclusion of several potentially important risk factors. For example, the significant impact of the COVID-19 pandemic has not been formally integrated or quantified.

Another notable limitation of the study is variable data quality and inconsistent availability. Lack of data made it difficult to estimate the RR given the significant heterogeneity across a number of socioeconomic factors.

In the future, GBD should expand its coverage of risk factors, especially for outcomes that contribute significantly to the burden of disease, such as mental disorders and musculoskeletal diseases. Mental disorders account for 5.4% of global DALYs, but only 8% of mental disorders were attributed to risk factors. Similarly, musculoskeletal diseases account for 5.6% of the global burden; however, in the current GBD, only 20.5% of this burden was attributable to risk factors.