Vitamin D supplementation shows promise as a way to help prevent dementia, new research suggests. Dementia is associated with “several diseases that affect memory, thinking, and the ability to perform daily activities,” according to the World Health Organization (WHO).
Over 55 million people in the world have dementia, with 10 million new cases every year. Risk factors include age, high blood pressure, diabetes, obesity, smoking, alcohol, depression, and a sedentary lifestyle. Alzheimer’s disease is the most common type, comprising about two-thirds of cases.
Conflicting results have been reported in past research about vitamin D supplementation and dementia prevention. In one 2021 systematic review with 20 randomized controlled trials (RCTs) containing between 30 and over 4,000 participants 18 years and older, half of the RCTs had mixed results, one quarter had negative results, and one quarter had positive results.
The confidence of the results was limited by differences in vitamin D levels in the blood, cognitive tests used, doses of vitamin D taken, and patient demographics. Another 2021 systematic review and meta-analysis included nine RCTs with 2,345 participants 60 years and older, but did not support the beneficial effect of vitamin D supplementation on preventing Alzheimer’s disease.
Promising but inconclusive results
Researchers from Canada and the UK dove further into the association between vitamin D supplementation and the incidence of dementia. The study was published in the Alzheimer’s & Dementia journal in March.
A total of 12,388 initially dementia-free U.S. participants from the National Alzheimer’s Coordinating Center (NACC) were followed between 2005 and 2021. The mean age was about 71 years old. Annually, 16 data-collection forms were filled out regarding demographic and clinical information.
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The vitamin D-exposed group (D+) included participants with baseline exposure to the vitamin D supplements of calcium-vitamin D, cholecalciferol (vitamin D3), or ergocalciferol (vitamin D2). While cholecalciferol is only found in animal products such as egg yolks and fish, ergocalciferol is produced by plants and mushrooms.
The non-exposed (D-) group did not have exposure to vitamin D supplements throughout all visits before a dementia diagnosis. Compared to the 7,751 people in the D- group, the 4,637 people in the D+ group had more education, more females, fewer Black participants, less mild cognitive impairment (MCI), and less depression.
Ten years after their baseline visit, 2,696 participants had developed dementia, 2,017 (75 percent) of which had no vitamin D exposure throughout all visits prior to their diagnosis, and 679 (25 percent) who had baseline exposure.
In a ScienceDaily news release, lead researcher Professor Zahinoor Ismail of the University of Calgary and University of Exeter said, “We know that vitamin D has some effects in the brain that could have implications for reducing dementia, however so far, research has yielded conflicting results.”
Not so general
Overall, exposure to all formulations of vitamin D was associated with a 40 percent lower incidence of dementia compared to no exposure. Based on subgroup analyses, there were additional smaller groups that were found to have even greater benefit.
The effects of vitamin D were more pronounced in females compared to males and in participants with normal cognition compared to those with mild cognitive impairment. Those who were not carriers for the APOEe4 gene, which is associated with late-onset sporadic Alzheimer’s disease, had better results with vitamin D supplementation compared to carriers.
“Our findings give key insights into groups who might be specifically targeted for vitamin D supplementation. Overall, we found evidence to suggest that earlier supplementation might be particularly beneficial, before the onset of cognitive decline,” Ismail said.
However, the study has limited generalizability due to the fact that the participants, especially those in the vitamin D-exposed group, tended to be highly educated and White.
Future studies are needed to evaluate the different baseline vitamin D and calcium levels, exposure durations, dose-response relationships, socioeconomic statuses, sleep patterns, comorbidities, and social interactions.