US scientists have examined the biological processes behind five widely used ageing tests, finding that different methods appear to capture different aspects of how the human body ages.

Researchers analysed blood samples from 3,227 people who took part in the US Health and Retirement Study. They compared five commonly used epigenetic clocks with patterns of gene activity in the participants’ blood to determine what biological changes were associated with faster ageing according to each test.

Epigenetic clocks are mathematical tools that estimate biological age using DNA methylation, chemical changes that can influence how genes function without altering the underlying genetic code.

Scientists have increasingly used these clocks to investigate links between biological ageing, disease, physical decline and the risk of death. However, researchers have not always known precisely what processes inside the body were being reflected when a clock indicated that someone was ageing faster than expected.

The new study found that the five clocks were associated with different molecular signs of ageing. Some were more strongly connected to processes involved in energy use and cell growth, while others showed stronger links to immune activity and inflammation.

Despite those differences, the clocks shared several biological features. These included changes involving the immune system, metabolism and communication between cells.

The findings could help researchers select the most appropriate biological ageing test for a particular study. A clock associated more closely with immune activity, for example, could be more useful for research into immune-related ageing than one that primarily reflects metabolic changes.

The researchers also developed new measures called transcriptomic ageing gene scores, or TAGS, based on the molecular patterns identified in their analysis.

According to the study, TAGS in several cases performed better than the ageing clocks alone when predicting health outcomes. These included frailty, walking speed, heart disease, diabetes, lung disease and mortality.

T. Em Arpawong, a research associate professor at the USC Leonard Davis School of Gerontology, said ageing is not determined simply by chronological age but also by biological changes taking place inside cells.

Senior author Eileen Crimmins said the study helps explain what is happening beneath the surface when biological ageing tests produce their results.

By identifying the molecular processes associated with individual ageing clocks, researchers may be able to interpret their readings more accurately and understand which tools are best suited to different areas of ageing research.

The findings could eventually support research into preventing age-related illness and identifying people at higher risk of declining health. However, the study focuses on biological markers and does not mean the new measures are ready to replace clinical assessments of health or provide individual predictions of lifespan.

Researchers said the work provides a clearer picture of the biological mechanisms captured by ageing clocks and could guide their use in future studies of ageing and disease.

Heatwaves are becoming more frequent and severe, yet a large proportion of people in England are failing to take protective measures after receiving official warnings, according to a new study.

Research by experts at United Nations University found that 41 percent of people who had seen a Heat Health Alert took no action to protect themselves from extreme temperatures.

The study surveyed 1,097 adults across England and interviewed 29 professionals involved in communicating heat risks. Around seven in 10 people surveyed said they had encountered a Heat Health Alert, but many did not respond to the warnings.

The main reason was a low perception of personal risk. Only 18.1 percent of respondents said they considered themselves at high risk from extreme heat.

About 30 percent said they had limited or no knowledge of measures that could protect them during periods of extreme temperatures.

Other reasons for inaction included failing to recognise the alert, uncertainty about what steps to take and difficulty understanding the information. Around 19 percent cited low personal risk perception, 9 percent did not recognise the alert, 7 percent were unsure what action to take and 5 percent found the warning difficult to understand.

Researchers said the findings show that issuing warnings alone does not guarantee that people will change their behaviour. People need to understand the health risks, recognise that those risks may apply to them and receive clear instructions about what they should do.

The way warnings are delivered may also be limiting their reach. About 90 percent of heat-risk communication professionals surveyed said they used digital platforms to distribute information.

However, around 30 percent of respondents said they had not encountered heat warnings or information about protecting themselves from heat at all. Social media was also identified as the least trusted source of heat-related information, particularly among older people.

The researchers recommended using trusted community organisations to reach people who may be missed by digital communication. Libraries, community groups, social care organisations, voluntary bodies and faith groups could all play a larger role in spreading heat-health information.

Authorities should also assess whether warnings actually change behaviour rather than simply measuring website visits, media coverage or social media activity, researchers said.

The study also found that vulnerability to extreme heat extends beyond individual awareness. Housing quality, poverty, existing health conditions, environmental exposure and access to resources can all influence the impact of heatwaves.

Researchers therefore called for a broader approach that goes beyond issuing alerts. They said heat resilience should be built into housing standards, planning policies and home improvement programmes, with stronger enforcement of measures designed to prevent buildings from overheating.

As extreme heat becomes a growing public health threat, the study argues that England needs to ensure warnings are not only received but understood and acted upon, while reducing the underlying conditions that leave people vulnerable.