In a recent study conducted and published in BMC Medicine, the impact of flooding on mortality rates over the long term was investigated by researchers.
Study: Floods and cause-specific mortality in the UK: a nested case-control study. Image Credit: Valery Zotev/Shutterstock.com
Background
Floods present a significant global challenge, resulting in fatalities, property destruction, and disruptions to critical services like water, communication, energy, and public transport. They can also lead to infections, accidents, and exposure to harmful chemicals.
Floods can exacerbate noncommunicable diseases such as cardiovascular ailments, cancer, chronic respiratory conditions, and diabetes. Stressors can contribute to mental health issues with lasting health implications.
However, there is a lack of comprehensive epidemiological data on the long-term impacts of flooding on mortality rates and limited research on the consequences of flood exposure.
About the study
In this study, researchers investigated the effects of flood exposure on mortality outcomes.
The team collected flood data from the Dartmouth Flood Observatory (DFO) spanning 2000 to 2020 and matched it with data from 499,487 participants in the United Kingdom Biobank.
Participants, aged 37 to 73 years, were recruited from 21 centers in Scotland, Wales, and England between 2006 and 2010. Those without residential latitude and longitude data or lacking information on ethnicity, age, gender, sex, and deceased status within the recruitment year were excluded.
Participants were monitored until the end of the study period (December 31, 2020) or their demise, whichever came earlier. Yearly cumulative flood exposure was calculated by multiplying flood duration and severity and summing up the values for each year.
The researchers analyzed the risks of any-cause and specific-cause mortality linked to flooding using the International Classification of Diseases, tenth edition (ICD-10) codes and examined lag patterns in mortality risks.
Each case was matched with eight controls, and flooding exposure was modeled using non-linear and lag-type conditional logistic regressions to determine odds ratios (OR) for analysis.
Study variables included education level, body mass index (BMI), diet quality, physical activity, overall health assessment, smoking status, alcohol consumption, annual income, and Townsend deprivation index (TDI).
Hourly humidity and temperature data were obtained from the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA-5) dataset, and meteorological data were mapped to the residential addresses of participants.
Results
The average age of participants was 61 years, with 59% males (n=170,549) and 97% white individuals (n=281,175). The researchers documented 33,021 deaths in total.
Deceased individuals were more likely to smoke, have higher BMI, lower household income, and university education. They consumed fewer fruits and vegetables, more processed and red meat, and rated their health as fair to poor.
After adjusting for confounders, the risk of any-cause mortality increased by 6.7% (OR: 1.1) per unit rise in flooding index. In the raw model, each unit increase in flooding index raised the risk of any-cause mortality by 9.2% (OR: 1.1), with consistent results after adjusting for socioeconomic factors (OR: 1.1) but a diminished association after adjusting for lifestyle habits.
Similar effects were observed for specific-cause mortality in the fully adjusted model, where higher flooding index levels were linked to increased risks of death from neurological diseases (OR: 1.1), cancers (OR: 1.1), respiratory disorders (OR: 1.1), suicides (OR: 1.1), cardiovascular diseases (OR: 1.1), mental disorders (OR: 1.1), and digestive disorders (OR: 1.0).
For any-cause mortality, the relationships’ strength increased from recent times (OR: 1.0) to the third lag year (OR: 1.0) and decreased to zero by the fifth lag year. Mortality risks related to neurological and mental disorders were minimal during the current period but peaked in the third and fourth lag years.
Interestingly, suicide-related mortality risks were highest in current times (OR: 1.0) and diminished by the fifth lag year.
Individuals with higher education levels and incomes exhibited elevated mortality risks for most causes, with individuals at higher risk for suicides being obese, consuming less alcohol, residing in more deprived regions with lower income and physical activity levels.
Women under 64 years had higher mortality risks from any cause, including respiratory diseases and cancers, but lower risks from mental and digestive disorders.
Sensitivity analyses using imputed data points did not alter the findings, and the results remained unaffected by the COVID-19 pandemic.
Odds ratios for any-cause deaths and tumors increased slightly, whereas other causes showed stable trends. The odds of any-cause deaths rose with higher monthly flooding indices.
Conclusion
The study indicated that prolonged exposure to floods escalates mortality risks, with varying lag periods for different causes of death. Such exposures have enduring effects on neurological and mental health, alongside acute impacts on suicide rates.
The groups vulnerable to flood-related deaths varied based on the cause of death. Over six years, every unit increase in flood index heightened the risk of all-cause mortality by 6.7%.
Flood exposure can lead to various health consequences over time. These findings could inform public health policies and mitigate the health burdens resulting from floods.
