For the first time, researchers have detected possible signs of Alzheimer's disease in the brains of adults who were as young as 20 years old, upending the notion of the disease as an elderly affliction. Scientists have long known that clumps of a protein known as amyloid build up in the brains of older Alzheimer’s patients but researchers have now spotted groups of these proteins in the brains of young adults who were otherwise healthy and fully expected to live many more years with normal cognition.

While all humans begin producing amyloid as soon as they are born, the tell-tale sign of Alzheimer’s was long thought to be when these sticky proteins start to bind to one another. Researchers from Northwestern University searched for this amyloid build-up in the brains of 50 deceased people whose organs had been donated to the university’s Alzheimer’s Disease Centre Brain Bank and published their results on Monday in Brain.

In their hunt, researchers honed in on a group of cells associated with memory and attention and which are often the first to die as a person ages. The scientists fully expected to find bunches of amyloid proteins in and around these cells in the brains of older patients who had been diagnosed with dementia, but were surprised to find that the proteins had already begun to build up even in the youngest brains they analyzed. The youngest person in their sample was only 20 years old.

“What's interesting is that we see this phenomenon in such young individuals and these are people who will live with normal cognition for many years,” Alaina Baker-Nigh, a co-author and neuroscientist at Washington University in Saint Louis, Missouri, says. “It's possible that these cells are essentially healthy or only slightly affected for many, many years until something triggers the process of cell death.” Another protein called tau which is affiliated with the spread of the illness may be to blame.

Alzheimer’s disease is the most common form of dementia and afflicts 5.2 million Americans, according to the Texas Department of State Health Services. About 44 million people worldwide suffer from it or another form of dementia, according to a 2014 report by Alzheimer’s Disease International. Baker-Nigh points out that the disease will only become more common as the population grows older, since it develops as a natural part of aging. She also notes that people with genetic mutations which predispose them to Alzheimer’s may show amyloid clumps in their brains as early as their teens, but her work focuses on those without mutations.

Based on the results, the researchers realize that people may live with amyloid protein build-up long before they develop Alzheimer's disease. Baker-Nigh says this knowledge may prompt drug companies and researchers who have so far failed to treat the disease in its later stages to start thinking about much earlier interventions.

"There's definitely a move within the field to look younger and younger,” she says. “One of the reasons that has been floated as to why all the drug trials have failed is partly because we're looking too late. By the time the cells are dying, it's too late to halt that cognitive process." The size of the clumps she detected in younger people was, on average, smaller than those which occurred in older adults.

For those who find the news disconcerting, there are several steps that experts say may reduce the likelihood that adults of any age will develop Alzheimer's disease. The Alzheimer's Association recommends adopting a Mediterranean diet  and taking college or online courses throughout all stages of life to stay mentally sharp.  The U.K.'s National Health Service suggests not smoking and drinking alcohol in moderation -- both are steps that lower a person's likelihood of developing cardiovascular disease which has been linked to dementia.  The Mayo Clinic adds that exercising for 30 to 60 minutes a day several times a week may delay the disease's onset.