A new international study led by University of Galway suggests that having higher levels of vitamin D in middle age is associated with lower levels of tau protein in the brain, which is a sign of dementia, years later.

The study does not prove that vitamin D levels lower the level of tau in the brain or the risk of dementia; it only shows an association. 

The findings have been published today in Neurology Open Access, an official journal of the American Academy of Neurology.

Study findings

• Higher vitamin D levels are associated with lower levels of the Alzheimer’s biomarker, tau protein in the brain, years later.
• Higher vitamin D levels may protect against dementia.
• The study does not prove cause and effect; it only shows an association.
• The results need to be confirmed with additional studies.

The study was led by Professor Emer McGrath and Dr Martin Mulligan, from the College of Medicine, Nursing and Health Sciences at University of Galway and Galway University Hospital. It was carried out in collaboration with Boston University, the Framingham Heart Study and University of Texas San Antonia.

Senior author, Professor Emer McGrath, Associate Professor in Medicine, University of Galway and Consultant Neurologist, Galway University Hospital, said: “This study demonstrates an association between higher vitamin D in mid-life and a lower burden of abnormal tau protein in the brain, a marker of Alzheimer’s disease. Vitamin D in mid-life could be an important factor to protect future brain health. While previous research has linked low vitamin D in adults over 70 with an increased risk of dementia, this study is among the first to look at younger adults at mid-life, around the average age of 39. Low vitamin D in mid-life may be an important target to reduce the risk of early signs of preclinical dementia in the brain.

“However, while these findings are very interesting, they only demonstrate an association between vitamin D and early signs of dementia in the brain. Further studies, for example a clinical trial, will be required to determine if vitamin D supplements could prevent dementia."

Lead author, Dr Martin Mulligan, PhD researcher at University of Galway, said: "We found that higher vitamin D levels were associated with lower tau deposition in regions of the brain that are known to be affected earliest in Alzheimer's disease. 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. However, these results need to be further tested with additional studies.”

The study involved nearly 800 people with an average age of 39 who did not have dementia.

All participants had the level of vitamin D in their blood measured at the start of the study. They had brain scans an average of 16 years later that measured levels of tau and amyloid beta proteins in the brain, which are both biomarkers for Alzheimer’s disease. A high level of vitamin D was defined as greater than 30 nanograms per milliliter (ng/mL) and a low level was less than that number.

A total of 34% of participants had low levels of vitamin D and 5% were taking vitamin D supplements. The results took into account other factors that could affect tau levels, such as age, sex and symptoms of depression.

The results showed that higher vitamin D levels are associated with lower levels of the Alzheimer’s biomarker tau protein years later.

Dr Mulligan added: “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. Mid-life is a time where risk factor modification can have a greater impact.”

A limitation of the study is that the blood level of vitamin D was measured only once.

Professor McGrath added: “The findings do support the need for clinical trials to determine if Vitamin D supplementation in younger adults could delay or help prevent the onset of dementia."

The Framingham Heart Study is the longest running longitudinal cohort study worldwide. It started in 1948 with the recruitment of 5,200 adults from the town of Framingham in Massachusetts, Boston, with approximately 15% of the participants of Irish ancestry.

The study was supported by the National Institute on Aging, National Institute of Neurological Disorders and Stroke, Irish Research Council and Health Research Board of Ireland.

The full study can be read here.

Ends