An infection that hits one in three adults at some point may dramatically increase the risk of early-onset dementia, experts have warned.
A study spanning more than two decades found that adults aged 50 and over who were hospitalised with shingles were seven times more likely to develop the memory-robbing condition.
Crucially, the greatest risk was seen in those aged 50 to 65, which is younger than the typical age of dementia patients.
The new findings add weight to calls for wider access to the shingles vaccine, which is currently only given in the UK to over 65s, or those aged 70 to 79 who have not had a jab.
Shingles is caused by the varicella zoster virus—a member of the herpes family that most people contract as children, and also causes chickenpox.
Once a person is infected, the virus stays dormant in the body but can, if the immune system is temporarily weakened, reactivate.
This blistering painful rash, typically confined to one area—usually one side of the face or body—is shingles.
Why this occurs isn't fully understood however it is most commonly seen in older people, who have naturally lower immunity.
A major study has found adults aged 50 and older who had been hospitalised with shingles are seven times more likely to develop the memory-robbing condition
Stress and other infections than temporarily weaken the immune system are also known triggers.
Alongside the skin symptoms, patients may suffer headaches, general flu-like symptoms and sensitivity to light.
Most cases are mild and resolve after two-to-four weeks, requiring little more than over-the-counter painkillers, the infection can be debilitating.
However, it can trigger complications such as inflammation in and around the brain, severe pain, and affect the eyes, all of which require hospital treatment.
Those most at risk of severe shingles are people with conditions that affect the immune system or who are on immune-suppressing drugs, as well as older adults.
In the new study, the Italian researchers recruited 132,986 adults aged 50 and older.
Of these, 12,088 were hospitalised with a diagnosis of shingles—termed 'herpes zoster disease' in the study.
They were then followed for a 23-year period, along with 60,440 adults from the general population and 60,440 who had been hospitalised with other infections.
British drugs giant GSK is investigating whether its shingles vaccine reduces the risk of dementia, which is the country's biggest killer, claiming 75,000 lives every year
Experts are encouraged by the findings given the lack of a cure or treatment for dementia, which affects almost one million Britons and almost seven million patients in the USA
After just one year, there was a two-fold increase in early dementia seen in the severe shingles group, compared to those in the other two groups.
And after 10 years, the risk for dementia was 22 per cent higher in the shingles group.
When adults aged 50 to 65 years were looked at alone, those hospitalised for herpes zoster showed a sevenfold higher risk for dementia.
' findings support improving immunisation public health strategies and extending the vaccination recommendations to younger people,' the authors wrote.
In the UK, about 194,000 people in England and Wales and one million people in the US develop shingles annually.
A growing body of evidence suggests herpes viruses may be behind cases of dementia.
Earlier this year researchers from Uppsala University in Sweden found that people who have been infected with the herpes simplex virus (HSV)—which causes cold sores—at some point in their lives were twice as likely to develop all forms of dementia, compared to those who were never infected.
And in March it was revealed that British drugs giant GSK is investigating whether its shingles vaccine can provide protection against the neurodegenerative disease.
A new four-year project aims to confirm growing evidence that the Shingrix vaccine—already available on the NHS—can reduce risk of dementia by up to 27 per cent, compared with the older Zostervax jab, which also appears to offer some protection.
Experts are encouraged by the findings, particularly given the lack of a cure or effective treatment for dementia, which affects almost one million Britons and almost seven million patients in the USA.
Existing drugs such as lecanemab and donanemab have shown promise but are not considered cost-effective for NHS use.
If Shingrix is proven to provide protection, it could mark a major breakthrough—offering millions of older adults access to a dementia-reducing vaccine already rolled out nationwide.
Although it isn't fully understood why herpes viruses may increase dementia risk, there is also some evidence that it can travel to the brain, triggering inflammation that leads to long-term damage.