Inflammation, often seen as a villain in relation to health, may protect against heart disease, a study has suggested.

Scientists were surprised by the finding because they suspected inflammation was likely to increase the risk of heart and artery disease, not reduce it.

Although inflammation is part of the body’s immune response, it can also be damaging and even life-threatening when its effects are too strong.

It also plays a leading role in auto-immune diseases such as rheumat-oid arthritis.

The new research, which involved data from more than a million men, looked for individuals with genetic variants that naturally dampen inflammation by blocking an immune system messenger molecule called interleukin-1.

As expected, people with this trait had a reduced risk of developing rheumatoid arthritis. But putting a brake on inflammation was actually found to increase the risk of heart attacks by 15 per cent.

Raised levels of harmful LDL (low-density lipoprotein) cholesterol were seen in these individuals.

Blocking interleukin-1 also increased an individual’s risk of experiencing an abdominal aortic aneurysm, a swelling of the main blood vessel leading away from the heart through the abdomen. One in 50 deaths of men over the age of 65 are caused by such aneurysms rupturing.

The genetic effect observed in the study mimicked that of the anti-inflammatory drug anakinra, said the researchers.

It suggested that the drug could potentially increase the risk of heart disease and abdominal aortic aneurysms, they added.

John Danesh, from Cambridge University, said: “Drugs such as anakinra are licensed for the treatment of inflammatory conditions including rheumatoid arthritis, but we know little about the long-term health consequences of blocking interleukin-1.

“Our approach was to use ‘nature’s randomised trial’ to get answers currently beyond the resolution of drug trials. Our genetic analysis suggests, surprisingly, that blocking interleukin-1 over the long term could increase the risk of cardiovascular diseases.”

Co-author Daniel Freitag, from the same Cambridge team, said: “The common view is that inflammation promotes the deve-lopment of heart disease − we’ve shown that the truth is clearly more complicated.

“We need to be careful that drugs like anakinra that aim to tackle rheumatoid arthritis by inhibiting interleukin-1 do not have unintended consequences on an individual’s risk of heart disease.”

Peter Weissberg, medical director at the British Heart Foundation, which co-funded the study, said: “It is important to remember that this is not a study of an anti-arthritis drug but a gene that can mimic its effects. The effects of a gene are lifelong, whereas a drug affects a person only while it is being taken.

“Nevertheless the study suggests that patients who are prescribed anakinra should have their cardiovascular risk factors carefully managed by their doctor.”

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