People with repeated hospital-treated infections, particularly in early and mid-life, may be more likely to develop Alzheimer's and Parkinson's, according to a 2022 Swedish study.
Alzheimer's disease is a type of dementia that affects memory, thinking and behavior.
The main symptoms include memory loss, confusion, disorientation as well as difficulty understanding and concentrating. For most people with Alzheimer's, symptoms start to appear in their mid-60s.
However signs of early onset Alzheimer's can surface in people as early as 30.
Parkinson's disease is a brain disorder that causes unintended or uncontrollable movements, such as shaking, stiffness, and difficulty with balance and coordination.
The international researchers analysed more than 290,000 Alzheimer’s cases and 103,000 Parkinson’s cases which were diagnosed in Sweden between 1970 and 2016.
They found a hospital-treated infection five or more years before a diagnosis had a 16% higher risk of Alzheimer's and a 4% higher risk of Parkinson's.
This increased to a 50% increased risk for Alzheimer's and a 40% higher risk for Parkinson's if the person was hospitalised multiple times for treatment of infections before the age of 40.
“These findings suggest that infectious events may be a trigger or amplifier of a pre-existing disease process, leading to clinical onset of neurodegenerative disease at a relatively early age,” the authors say.
The study points out that “due to the observational nature of the study, these results do not formally prove a causal link”.
Covid-19 linked to increased risk of Alzheimer's
Another international study by Case Western Reserve University in Ohio found the risk factor for developing Alzheimer's increases by 50 to 80% in seniors who caught Covid-19.
The researchers found people 65 and older who contracted Covid-19 were more prone to developing Alzheimer's disease in the year following their Covid-19 diagnosis, with the highest risk for women at least 85 years old.
The true impact of Covid-19 will take years to uncover
Cellular immunologist and long Covid-19 researcher Anna Brooks says Covid-19 infection does seem to be linked to neurological impacts, however it is hard to tell how devastating this will be in the future.
“We know that neurological symptoms are absolutely happening across the board with every single variant.
“But it’s going to be quite some time to see the true impacts of this virus because you wouldn't necessarily see the onset of a full-blown neurological disorder immediately. And that's why we want to keep raising the alarm.”
Brooks says it appears younger people are at a higher risk of reinfection because of waning immunity and the fact that people under 16 still aren’t eligible for a booster shot.
“With younger ones who may get Covid-19 mildly the first time, if you don't have a robust immune response the first time, you don't have an amazing level of immunity to protect you the second time. And therefore, they're more likely to get Covid-19 again.”
Brooks says large-scale studies on brain scans and cognitive function that will develop over time will be crucial.
“Many people may be recovering from Covid-19 well, but what's going to happen in five years, or 10 years time? That's what we really should be worried about.
“So it’s about trying not to get infected in the first place, or if you have, really trying not to be reinfected because this will increase your risk profile.”
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