A Harvard University expert has warned those with allergies to consider alternatives to antihistamines, following research linking the popular medication to a raised risk of dementia.
Writing on the prestigious university’s website, a top medic told of studies suggesting the over-the-counter pills could block a protective chemical in the brain that can ward off the disease.
Dr Anthony L Komaroff, an experienced family doctor and editor in chief of the Harvard Health Letter, said while the risk was still theoretical, it had led him to think twice before taking such drugs.
‘I weigh the symptom relief they give me against the possibility that they may slightly increase my risk of developing dementia,’ he wrote.
‘I ask if there are other drugs that might also give me symptom relief, without the theoretical risk of cognitive decline. I also use the lowest possible dose to get symptom relief.’
The warning comes just few weeks before the UK enters hay fever season – which starts from late March and lasts until September.
Approximately one in four Brits— about 16million people — suffer from hay fever and many turn to antihistamines tablets and sprays for relief.
Dr Komaroff said the theoretical risk posed by antihistamines was linked to how they work to stop allergies from causing symptoms like sneezing, coughing and itchy eyes.
Some studies suggest antihistamines, commonly taken for hay fever, are linked to increased dementia risk.
He explained the drugs are known as anticholinergics – which means they interfere with the brain’s release of a vital chemical called acetylcholine.
While this effectively limits allergic symptoms, low levels of the substance are linked dementia.
Dr Komaroff said: ‘Theoretically, these drugs might increase the risk of dementia by blocking a particular brain neurotransmitter [brain chemical] or increasing brain inflammation.
However, he said it was key to remember the science of this theory isn’t yet settled.
‘In the past decade, several studies have suggested that these pills might increase the risk of dementia, while other studies have found no risk. And all the studies are inherently flawed,’ he said.
Studies that have found a link between the drugs and dementia include one 2015 paper that tracked the brain health of more than 3,400 participants over 65 years old between 1994 and 2012.
Researchers found there was a link between increased doses of anticholinergics and those that developed dementia.
A separate 2024 study published in the Journal of Allergy and Clinical Immunology also revealed a link between antihistamines and dementia.
But they can also be a sign of dementia — the memory-robbing condition plaguing nearly 1million Brits and 7million Americans
Researchers conducted a retrospective cohort study using data from Taiwan’s National Health Insurance Research Database from 2011 to 2017.
It included more than 700,000 patients with recent-onset allergic hay fever. They were split into groups — those that didn’t take antihistamines and those that did.
After making adjustments for preexisting medical conditions, the researchers found there was a dose-dependent increase in dementia risk.
Hay fever drugs aren’t the only anticholinergic medications commonly taken.
Other examples include some sleep medications, those treating urinary incontinence, nausea, muscle tension and Parkinson’s disease.
In December, a British study on more than a million people found taking anticholinergics was linked to an 18 per cent increased risk of dementia diagnosis.
Men were slightly more vulnerable — their increased risk was 22 per cent, compared to women at 16 per cent.
Dementia has a variety of causes, two of the most common being Alzheimer’s disease and a reduced blood flow to the brain following a stroke, known as vascular dementia.
Around 900,000 Britons are currently thought to have the memory-robbing disorder. But University College London scientists estimate this will rise to 1.7 million within two decades as people live longer. It marks a 40 per cent uptick on the previous forecast in 2017
Recent analysis by the Alzheimer’s Society estimated the overall annual cost of the dementia to the UK is £42billion a year, with families bearing the brunt.
An ageing population means these costs — which include lost earnings of unpaid carers — are set to soar to £90billion in the next 15 years.
Around 944,000 in the UK are thought to be living with dementia while the figure is thought to be around 7million in the US.
Memory problems, thinking and reasoning difficulties and language problems are common early symptoms of the condition, which then worsen over time.
A separate Alzheimer’s Research UK analysis found 74,261 people died from dementia in 2022 compared with 69,178 a year earlier, making it the country’s biggest killer.
