Forgetfulness and confusion have long been treated as an inevitable part of growing older. But a growing body of data suggests something more troubling is happening well before old age arrives. Rates of early-onset dementia and Alzheimer's disease among Americans younger than 65 reportedly doubled between 2013 and 2017, according to data from Blue Cross Blue Shield — and researchers are working to understand why.
A large study published in JAMA Neurology, drawing on data from more than 356,000 people in the UK Biobank, set out to identify the risk factors behind young-onset dementia. The average age of someone living with the condition was just 49, with women disproportionately affected. Fifteen lifestyle and health factors emerged as significant — some familiar, and some genuinely surprising.
The Familiar Risks, and the Unexpected Ones
Alcohol misuse, stroke, and hearing impairment topped the list — all previously linked to cognitive decline in other research. But the study also surfaced factors that hadn't been explored in this kind of depth before: vitamin D deficiency, elevated inflammatory markers (C-reactive protein, particularly in women), orthostatic hypotension, and social isolation.
"Young-onset dementia has a very serious impact, because the people affected usually still have a job, children, and a busy life," said Stevie Hendriks of Maastricht University, the study's lead author. "The cause is often assumed to be genetic, but for many people we don't actually know exactly what the cause is."
What the Vitamin D Connection Suggests
Vitamin D deficiency is remarkably common — an estimated 35 percent of adults in the United States fall short of adequate levels. Its appearance on this list isn't entirely new territory; prior epidemiological research has also connected low vitamin D to elevated dementia risk.
One study published in Alzheimer's & Dementia followed over 12,000 adults without a dementia diagnosis at baseline. Among those who went on to develop dementia within ten years, the large majority had not been taking a vitamin D supplement. Overall, supplementation was associated with a 40 percent lower incidence of dementia — with the protective effect appearing strongest in women, and strongest when supplementation began before any cognitive symptoms appeared.
That timing detail matters. It points toward vitamin D playing a role earlier in the process, well before decline becomes noticeable — which is consistent with what we understand about vitamin D's broader role in neurological and immune function, not simply bone health.
It's worth holding this alongside the caution from the Alzheimer's Association's Claire Sexton, who noted that randomized controlled trials on vitamin D and cognition have produced mixed results. Association isn't proof of cause, and more rigorous trials are still needed. What we can say with more confidence is that deficiency is common, correctable, and worth checking — regardless of what future trials ultimately show about its role in dementia specifically.
The Factors We Can Act On
Several of the identified risks are genuinely modifiable: alcohol use, diabetes, heart disease, and stroke risk (often tied back to blood pressure) all respond to lifestyle change — movement, dietary pattern, and smoking cessation among them.
Social isolation is a harder one to address, but no less important. The study found that people who saw friends or family less than once a month had higher rates of young-onset dementia — and the authors noted that isolation appeared to contribute to dementia risk independently of depression, not simply through it. Surgeon General Vivek Murthy has pointed to small, consistent acts of connection — answering a friend's call, sharing a meal, listening without a phone in hand — as meaningful starting points.
The Takeaway
None of this points to a single cause or a single fix. What it does offer is a more complete picture — one where a nutrient as ordinary as vitamin D sits alongside blood pressure, inflammation, and human connection as part of a modifiable risk profile, even for a condition long assumed to be driven mostly by genetics. A simple blood test and an honest look at how connected we're staying to the people around us may be more relevant to long-term brain health than most of us have been taught to think.
"I know that I know nothing." — Socrates