Vitamin D in Midlife Protects Against Alzheimer’s

People with higher blood levels of vitamin D during midlife were less likely to develop one of the brain changes associated with Alzheimer's disease years later, according to a new study published in Neurology Open Access.

Researchers found that adults who had higher vitamin D levels around age 40 also had lower levels of tau protein deposits in their brains about 16 years later. In Alzheimer’s disease, tau buildup damages and kills brain cells. Another protein implicated in Alzheimer’s disease that accumulates and forms damaging plaques, amyloid, was not associated with vitamin D levels. 

Maintaining adequate vitamin D levels during midlife could play a role in protecting the brain long before symptoms of dementia appear. Study author Martin David Mulligan of the University of Galway in Ireland said, “Mid-life is a time where risk factor modification can have a greater impact.” 

Laboratory studies have suggested that vitamin D may reduce the abnormal chemical changes that lead to tau build up. Vitamin D receptors are found throughout the brain, including areas involved in memory. Vitamin D also helps regulate inflammation and supports antioxidant defenses, both of which may protect nerve cells from damage.

Vitamin D

Vitamin D is in fatty fish (salmon, mackerel, tuna), egg yolks, liver, and mushrooms. Many foods are fortified with Vitamin D, such as non-dairy milks, cereals, and juices.

Sunlight on the skin makes the body produce vitamin D. The amount varies, depending on the season, the time of day, where a person lives, and skin color. Many health care professionals recommend supplementation, although Vitamin D supplements can interact with some medications.

Older adults are among those most likely to have low vitamin D levels because they often get less sun exposure and may not absorb the vitamin as efficiently. People with obesity, digestive disorders such as Crohn's disease and ulcerative colitis, and those who have had gastric bypass surgery are also at increased risk for vitamin D deficiency. Breastfeeding depletes Vitamin D. 

Low blood levels of vitamin D have already been linked to cognitive decline in the elderly. 

Looking for Early Signs of Alzheimer's Disease

Most previous studies examining vitamin D and dementia have focused on older adults after cognitive changes have already begun. In this study, researchers wanted to know whether vitamin D levels much earlier in adulthood were associated with biological signs of Alzheimer's disease before dementia develops.

The study included 793 participants from the Framingham Heart Study. Participants were free of dementia when they enrolled, with an average age of 39 years when their blood was tested for vitamin D. Approximately 16 years later, many underwent specialized PET brain scans that measured deposits of tau and amyloid proteins.

Higher Vitamin D, Lower Tau

After accounting for factors that could influence brain health like age, sex, blood pressure, smoking, diabetes, cardiovascular disease, depression, body mass index, and the season when blood samples were collected, researchers found a consistent relationship between vitamin D levels and tau accumulation.

Higher vitamin D levels were associated with lower amounts of tau throughout the brain as well as in regions that are among the first affected during Alzheimer's disease. The association remained significant even after being subject to additional analyses.

In contrast, vitamin D levels were not associated with amyloid buildup on brain scans. Vitamin D may influence some aspects of Alzheimer's disease biology more than others.

The researchers also found no evidence that the relationship differed between men and women or between people who carried the APOE ε4 gene, a common gene that is the strongest known genetic risk factor for Alzheimer's disease.

Study Limitations

The study does not show that taking vitamin D supplements will prevent Alzheimer's disease or reduce tau buildup, only that it might severe as a defense. “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 Mulligan.

Vitamin D was measured only once during midlife, and participants were followed observationally rather than being randomly assigned to receive supplements. Even so, the results point to vitamin D as a potentially modifiable factor that could influence brain health decades before dementia develops.

Because the participants were still relatively young when their vitamin D levels were measured, the findings also highlight the importance of studying Alzheimer's disease in the decades of life before memory problems become apparent.