Getting shingles just once could increase the risk of long-term confusion and memory loss, a new study has found.
The study, led by Brigham and Women’s Hospital and Harvard Medical School, linked the virus to greater chances of "subjective cognitive decline," according to a Harvard press release.
The findings were published in the journal Alzheimer's Research & Therapy on Aug. 14.
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"Subjective cognitive decline" captures early changes in cognition that are noticed before evidence of cognitive impairment shows up on standard neuropsychological tests, explained study author Sharon Curhan, M.D., a physician and epidemiologist at Brigham and Women’s Hospital in Boston.
It was also associated with a higher risk of mild cognitive impairment (MCI) and dementia.
"Shingles may contribute to dementia risk through neuroinflammation, damage to cerebral blood vessels (cerebral vasculopathy), or direct neuronal damage," Curhan told Fox News Digital.
In this particular study, the researchers analyzed data from three large cohorts of more than 150,000 women and men over a 13-year period.
The data came from the Nurses’ Health Study, the Nurses’ Health Study II and the Health Professionals Follow-Up Study, according to Curhan.
"There was a suggestion that the magnitude of the elevated risk may be greater among those who were not vaccinated with the shingles vaccine," she said.
The researchers determined that shingles was associated with a greater than 20% higher long-term risk of subjective cognitive decline.
"We were surprised by the large magnitude and long duration of the increased risk, and [the fact] that it may be different in women and men," Curhan told Fox News Digital.
The elevated risk was even higher among those who were genetic carriers of APOE e4 — the gene that increases the risk for Alzheimer’s disease — than men who were not APOE e4 carriers, she noted, but this was not the case in women.
Although he noted that this is an observational study and does not prove cause and effect, Dr. Marc Siegel, senior medical analyst for Fox News, said he believes "the observation is real."
"Shingles is a reactivation of a virus that has been hiding inside nerves," he told Fox News Digital. "It causes inflammation — and when inflammation involves the brain, it is associated with cognitive decline, which can lead to Alzheimer's."
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Previous studies have also looked at the association of herpes zoster and other viruses with Alzheimer's and the other diseases that cause dementia, according to Heather M. Snyder, PhD, senior vice president of medical and scientific operations at the Alzheimer’s Association in Chicago.
"It is unclear if the virus is present in individuals because of changes associated with the diseases that cause cognitive decline, changes of the immune system, or some sort of cause and effect," Snyder, who was not involved in the study, told Fox News Digital.
Previous research has also shown that a history of shingles is also associated with higher long-term risk of a major cardiovascular event, such as a stroke or heart attack, which could last for many years after infection, Curhan warned.
Shingles — medically known as herpes zoster — is a painful, blistering rash caused by the varicella-zoster virus (VZV), which is the same virus that causes chickenpox, according to the U.S. Centers for Disease Control and Prevention (CDC).
The rash and blisters usually scab over within seven to 10 days.
The infection is common, affecting about one in every three people in the U.S. in their lifetime.
"A majority of adults have herpes zoster hidden in their brain cells, from prior infection at some previous point in their life," said Snyder.
In addition to the rash — which typically appears as a stripe around one side of the body or face — symptoms can include fever, chills, headache and upset stomach, according to the CDC.
In some cases (10% to 18%), the virus can lead to complications like long-term nerve pain.
Other rare but serious adverse effects can include vision loss, bacterial infections, pneumonia, brain inflammation (encephalitis), impaired hearing and death, per the CDC.
These complications are most likely to affect those with compromised immune systems.
Antiviral treatments and pain relief medications are available for those with the condition.
These findings show the "long-term implications" of shingles and highlight the importance of public health efforts to prevent the infection, Curhan noted.
The vaccination has been shown to be 90% effective at preventing the infection and long-term nerve pain in adults age 50 and over who have healthy immune systems, according to the CDC.
"Given the growing number of Americans at risk for this painful and often disabling disease and the availability of an effective vaccine, shingles vaccination could provide a valuable opportunity to reduce the burden of subsequent health issues due to shingles, such as chronic pain (postherpetic neuralgia), cardiovascular complications, or cognitive decline and dementia," said Curhan.
The CDC recommends routine shingles vaccination for people age 50 and older, regardless of whether they have had a prior episode of shingles or have had a previous vaccine.
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"Anyone who may be eligible for the vaccine or who may have questions or concerns about vaccination should consult with a health care provider," said Curhan.
Siegel echoed the merits of vaccination.
"This study adds to the growing group of evidence that the shingles vaccine (Shingrix) is important for all those over 50 (who have had chicken pox or the varicella vaccine) to decrease the risk of reactivation of the shingles virus and/or complications of active infection," he said.
This was an observational study that primarily focused on a White, highly educated population, Curhan noted — which means future studies in other populations could strengthen the research.
"Also, we did not have information on vaccination status in the full study population, so we could only examine this relation among a subset," she added.
Much of the study period took place before the shingles vaccine became widely available, Curhan said — and even once it was introduced, the uptake was generally low.
The more recent vaccine was not available until after the study.
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"As uptake of the newer shingles vaccine increases, additional studies that evaluate whether vaccination status influences the relation of shingles and risk of cognitive decline would be informative," Curhan said.
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"Therefore, we are currently collecting this information among our participants and hope to conduct these studies in the future."
