That conclusion comes from a study of nearly half a million adults in the UK, led by researchers at the MRC Laboratory of Medical Sciences (LMS) and Imperial College London. The researchers believe it is the largest study of its kind.

Their findings suggest that chronic inflammation, which is associated with lifestyle and socioeconomic circumstances, may contribute to harmful changes in the heart's structure. It was also linked to a greater risk of heart attack and stroke.

Importantly, these changes may begin years before a person notices any cardiovascular symptoms, allowing the damage to build silently over time.

Hidden Inflammation May Change the Heart

Professor Declan O'Regan, British Heart Foundation Chair of Cardiovascular AI at Imperial College London and Head of the Computational Cardiac Imaging Group at the LMS, said: "Our study, which is the largest of its kind, suggests that millions of people could be living with hidden inflammation, which is slowly changing their heart and causing long-term damage - increasing the risk of heart attack and stroke. Chronic inflammation is complicated, but we know it's tied to our health and driven by a range of lifestyle and economic factors - meaning people may be at more risk just because of their surroundings, their economic status, their family's health and their lifestyle."

"But while tackling health inequalities remains an issue, there are things that we can do about inflammation, including reducing risk factors like smoking and obesity."

Chronic inflammation occurs when the immune system remains mildly activated for long periods rather than switching off after an immediate threat has passed. This persistent, low-level immune activity has been associated with several diseases, including cancer and diabetes, and researchers increasingly suspect that it may also play an important role in heart disease.

For the new study, the team examined UK Biobank data from nearly 480,000 adults in the UK. They assessed inflammation using a blood marker called glycoprotein acetyls (GlycA) and combined those measurements with heart imaging and genetic information.

A 43% Higher Risk of Heart Attack and Stroke

People with the highest inflammation levels (the top 20%) had a 43% higher risk of heart attack and stroke than participants with the lowest levels (the bottom 20%).

The researchers also found signs that inflammation was associated with physical remodeling of the heart. People with higher inflammation tended to have thicker heart walls, smaller heart chambers and poorer heart filling - all changes which may develop quietly for years before progressing to heart failure.

Inflammation was also strongly associated with socioeconomic disadvantage and psychological distress. More familiar cardiovascular risk factors, including smoking and excess body fat, were linked to higher inflammation as well.

People whose inflammation remained elevated over time had a 43% greater risk of heart attack and stroke, even when they had no previously existing heart disease.

The findings suggest that inflammation may provide one biological route through which pressures from everyday life, including poverty and mental health problems, can affect the body and increase cardiovascular risk.

Social Factors, Mental Health, and Genetics

Professor Declan O'Regan added, "The surprising thing was how much social factors and mental health are linked to inflammation and damage to the heart -- as well as more well-known risk factors like smoking and inactivity. There was also a strong genetic factor, with some people being naturally more resilient or susceptible to the inflammatory damage that comes from different lifestyles."

The researchers emphasize, however, that genetic susceptibility or difficult life circumstances do not make heart disease inevitable. There are still opportunities to reduce persistent inflammation and lower cardiovascular risk.

The analysis also highlighted inflammatory proteins in the interleukin-1 and TNF families as possible contributors to the observed heart damage.

Several of these proteins are already being targeted by drugs being tested in clinical trials. That raises the possibility that anti-inflammatory therapies could eventually help prevent cardiovascular disease before symptoms begin.

Blood Tests Could Help Identify People at Risk

The researchers also suggest that inflammation blood tests could potentially be combined with genetic risk scores to identify people who may benefit most from early intervention.

Professor Bryan Williams, Chief Scientific and Medical Officer at the British Heart Foundation, said: "Inflammation is part of the body's healing process, but there is also a darker side to it. This large-scale study found people with higher levels of inflammation experienced silent changes to the structure of their hearts and had a higher risk of major cardiac events including heart attacks and strokes."

"The research provides valuable insights into how our genes and lifestyle factors, such as smoking, poor mental health and socioeconomic status, can converge to trigger inflammation. It also identifies several inflammatory proteins that appear to play a key role in the heart changes linked to chronic inflammation, and it is to be hoped that anti-inflammatory medicines could become an important tool in preventing cardiovascular disease.

"These findings reinforce the importance of tackling the causes of inflammation and poor cardiovascular health, while also supporting people to make lifestyle changes that can help protect their hearts."

The study was funded by the Medical Research Council and British Heart Foundation.

The work was also supported by the NIHR Imperial Biomedical Research Centre, a translational research partnership between Imperial College Healthcare NHS Trust and Imperial College London.