Rhiannon Ingle
Many of us incorporate vitamins and supplements into our daily routine, with vitamin D being a popular choice for quite a few of us.
The NHS outlines that vitamin D helps regulate the amount of calcium and phosphate in the body, which are nutrients needed to keep bones, teeth and muscles healthy.
It's important we're getting enough of the stuff, as a lack of vitamin D can lead to bone deformities such as rickets in children, and bone pain caused by a condition called osteomalacia in adults.
Good sources of vitamin D, other than dietary supplements, include direct sunlight on the skin when outdoors as well as a small number of foods like oily fish, red meat and egg yolks.
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And while vitamin D is great for your physical health, it also supports overall brain health, with a study finding that higher vitamin D levels in midlife may be linked to lower tau protein levels, a marker of Alzheimer’s risk.
Alzheimer's disease is the most common cause of dementia in the UK.
An April 2026 study in Neurology Open Access, cited by Eating Well, followed 793 adults from the Framingham Heart Study. Participants were around 39 at the start, with no dementia.
Researchers measured vitamin D levels, then carried out brain scans roughly 16 years later, focusing on tau and amyloid beta, proteins linked to Alzheimer’s.
Higher vitamin D levels in midlife were associated with lower tau levels later on, while no link was found with amyloid beta.
"These results suggest that higher vitamin D levels in midlife may offer protection against developing these tau deposits in the brain and that low vitamin D levels could potentially be a risk factor that could be modified and treated to reduce the risk of dementia," said study author Martin David Mulligan.
Tau is a key marker in dementia research as lower levels tend to signal healthier brain ageing.
It's important, however, to note that the study shows a link, not proof of cause and effect.
There are limits, too, as vitamin D was measured once, not tracked over time. Other lifestyle factors may have influenced outcomes, even after adjustments.
With that said, midlife stands out as a window where habits matter.
"These results are promising, as they suggest an association between higher vitamin D levels in early middle age and lower tau burden on average 16 years later," Mulligan said. "Midlife is a time where risk factor modification can have a greater impact."