Air pollution and non-optimal ambient temperature are the top two environmental factors affecting human health and well-being worldwide. It is estimated that 5-9 million deaths each year are linked to air pollution, and 4-6 million to non-optimal ambient temperatures. However, substantial uncertainty persists about their relevance, both qualitatively and quantitatively, for specific diseases in diverse populations. Decade-long research in CKB has helped address some of the key knowledge gaps, via cross-disciplinary, international collaboration with world-leading experts in the UK and China. Using a prospective cohort approach, CKB has produced new evidence on the health impact of household air pollution from domestic solid fuel use on risks of a wide range of diseases including those affecting the cardiovascular and respiratory systems, the liver, and eyes. We have also clarified the role of ambient temperature on blood pressure, diagnosis and management of hypertension, and risks of cardiovascular disease in China. More recent work directly addresses the reliance on relatively crude outdoor exposure data in environmental epidemiology, and demonstrated the feasibility and importance of personal exposure measurements and modelling, using multi-modal data involving advanced wearable and static sensors.
Household air pollution
In the past few decades China has undergone rapid economic development and environmental changes. Worsening ambient air pollution in urban areas has caused immense public concern, but household air pollution, a much more intense, longstanding risk exposure, has been largely overlooked despite China still having ~500 million users of solid fuel during the 2010s.
In the past few decades China has undergone rapid economic development and environmental changes. Worsening ambient air pollution in urban areas has caused immense public concern, but household air pollution, a much more intense, longstanding risk exposure, has been largely overlooked despite China still having ~500 million users of solid fuel during the 2010s.
CKB showed that long-term solid fuel users have 10-20% higher risks of deaths, particularly from major cardiovascular and respiratory diseases, compared to clean fuel users (JAMA 2018; AJRCCM 2019; Lancet Glob Health 2020; Nat Hum Behav 2023). Importantly, these studies suggest that the potential harm of household air pollution could be at least partially mitigated through improved ventilation and use of clean fuels. CKB was the first epidemiological study to extend the harmful effects of air pollutants from cardio-respiratory systems to the liver, given its pivotal role of detoxification, showing that long-term solid fuel users had over 25% higher risk of deaths from major chronic liver disease (IJE 2020), including liver cancer (IJC 2022).
The eyes are very exposed to air pollution and most previous studies only investigated mild eye symptoms or cataract, however CKB demonstrated for the first time the increased risks of hospitalisation from a wide range of eye diseases, including cataract, conjunctiva disorders such as conjunctivitis (inflammation of the conjunctiva), and disorders of the sclera, cornea, iris and ciliary body such as keratitis (inflammation of the cornea) (PLOS Med 2021).
Non-optimal ambient temperatures
The ten CKB study sites cover a diverse range of climate zones, with, for example, average winter temperature ranging from -14°C to 19°C. We found a strong inverse relationship between ambient temperature and blood pressure (J Hypertens 2012). Overall, a 10°C drop in ambient temperature was associated with 6-7 mmHg rise in systolic blood pressure, with greater effects in older participants and those with low body mass index. Notably, people with pre-existing cardiovascular disease had a significant higher risk of dying in the winter months (Eur heart J 2015). CKB also identified clearly how temperature and seasons may influence the detection, diagnosis, and management of hypertension, indicating an under-diagnosis in warmer seasons and poorer management during colder seasons (J Hypertens 2012; IJE 2014). This research has major implications for the clinical management of hypertension and epidemiological research into the condition. Our findings have informed the design of periodic national surveys on blood pressure in China in recent years.
The widely different heating fuel use patterns across China enabled CKB to explore how various heating approaches may mitigate against the health effects of cold temperatures. Notably, individuals with well-established and universal central heating system in Harbin in northern China tended to have modest elevation of blood pressure during the winter, despite the region having the coldest winter of all ten CKB areas (J Hypertens 2012; Eur Heart J 2015). This offers an important insight into the significance of access to affordable clean energy and the increasing need for appropriate environmental and energy policies to reduce the threat to public health from increasingly extreme weather associated with climate change.
More recently, CKB began exploring the molecular impact of non-optimal temperatures on the plasma proteome, examining the concentrations of thousands of plasma proteins across a wide temperature range, from -27 °C to 30 °C. As one of the first studies of its kind, the analyses showed that almost 1000 proteins to be related to cold or heat exposure, shedding new light on the molecular mechanisms of the adverse health impact of cold or heat. These should inform future population health, clinical, and biomedical studies.
Enhanced personal exposure assessment
To improve the exposure assessment at personal level, increasingly, CKB has collected real-time measurements of air pollution and temperature exposure using advanced wearable and static sensors (Environ Int 2021). Through comparing the measurements across the personal, household, and outdoor environments, the researchers observed stark deviations between personal and outdoor measurements, clarified the roles of a wide range of behavioural and housing environment factors in determining personal exposure, and developed machine learning models in accurately predicting personal exposure based on more readily measurable data from questionnaires and static monitors (Environ Int 2024; Sci Total Enivron 2023).
Impact of research
The global health impact of air pollution and non-optimal ambient temperature will likely grow with the worsening global climate change and rapid industrialisation in emerging economies, unless strong action is taken to control them. CKB has produced novel evidence and methodologies to enable more accurate estimation of the disease burden linked to these exposures, inform clinical management of hypertension and cardiovascular disease, encourage better access to clean energy, and uncovered the molecular impact of temperature.