Vitamin D and Dementia: What’s All The Hype?
You may have heard some buzz all over your social media feed about a new study linking vitamin D to decreased dementia risk. It’s even received media coverage with click-bait type of headlines. As a dietitian, I wanted to read the study for myself to see if the buzz is worth all the hype.
What is dementia?
Dementia is a condition that commonly affects those who are older. According to the National Institute on Aging, it is characterized by a loss of cognitive functioning and can impact a person’s ability to think, remember, reason, and control their emotions [1]. It’s estimated that dementia effects nearly 50 million people worldwide, and that number is expected to triple by the year 2050 [2]. Because there is currently no cure, there has been a major focus on finding ways to mitigate a person’s risk.
What was studied?
In a prospective cohort study, researchers at the University of Calgary collected data from 12,388 dementia-free individuals through the National Alzheimer’s Coordinating Center database (which was established by the National Institute on Aging). Participants were put into two groups based on a medication form that was completed at their initial baseline visit: those who were exposed to a vitamin D supplement and those who were not. The final group of subjects consisted of 4,637 in the vitamin D group and 7,751 in the non-vitamin D group. The study described these two groups as “vitamin D exposed” or “non exposed” at baseline. However, the researchers did not assess whether the individuals supplemented with vitamin D throughout the duration of the study and they did not collect blood samples to measure the levels of vitamin D in the blood [2].
- Summary: The study investigated people over a period of many years. These individuals did not have dementia at the start, but may have developed it later. The researchers wanted to see if taking a vitamin D supplement had any effect on dementia incidence later in life.
What were the results?
After 10 years, 22% of the subjects developed dementia. Of those, 74% had no exposure to vitamin D prior to diagnosis. Those who were exposed to vitamin D at the onset of the study resulted in some intriguing outcomes, such as:
Vitamin D was associated with a 40% lower incidence of dementia compared to no exposure (after adjusting for age, sex, education, race, cognitive diagnosis, depression, and APOE4 status).
The 5-year dementia-free survival rate was significantly higher compared to no vitamin D exposure (83% vs 68%).
Women who were exposed to vitamin D had a lower incidence of dementia compared to men who were exposed to vitamin D.
Carriers of the APOE-4 gene had a lower dementia incidence rate when they were exposed to vitamin D compared to those who weren’t exposed. (This is interesting because having the APOE-4 gene is a strong risk factor for developing dementia).
- Summary: Overall, Vitamin D supplementation was associated with a 40% lower incidence of dementia and was particularly beneficial for those who are at a higher risk (such as women and those with a genetic predisposition).
What does this mean?
While this study had some interesting findings, there were quite a few limitations to the study itself that make it difficult to draw any hard conclusions. First of all, this was not a vitamin D supplementation study where subjects were required to take vitamin D every day for a specified period of time. Instead, the two groups were solely based on a medication questionnaire at the initial visit. If subjects marked that they were taking vitamin D, they were put into the vitamin D-exposed group and followed for several years. Essentially, this study evaluated if a subject took vitamin D at baseline, did they develop dementia throughout a 10 year timeframe. This leaves out important information such as the dose, frequency, and length of time they took a vitamin D supplement.
Another limitation is the researchers did not collect data on the vitamin D status of the blood. This is an important distinction that takes into account, not only vitamin D supplementation, but the amount of vitamin D in the body from all sources including food and sunlight. This was evaluated in a different study. Interestingly, vitamin D deficiency was associated with an increased risk of dementia and stroke [3].
However, in another published paper, researchers performed a systematic review and meta-analysis of 9 randomized clinical trials that evaluated Vitamin D supplementation on Alzheimer’s disease. The results did not find a beneficial effect on vitamin D supplementation on the prevention of Alzheimer’s disease [4].
- In conclusion, researchers are unclear if Vitamin D can help with dementia. And while the results of the study streaming across social media is extremely interesting, there were many limitations to the study and the jury is still out until more research is done.
References
1. What Is Dementia? Symptoms, Types, and Diagnosis. National Institute on Aging, NIH. Accessed March 23, 2023. https://www.nia.nih.gov/health/what-is-dementia
2. Maryam Ghahremani, et al. Vitamin D supplementation and incident dementia: Effects of sex, APOE, and baseline cognitive status. Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring (DADM). March 1, 2023. https://alz-journals.onlinelibrary.wiley.com/doi/full/10.1002/dad2.12404
3. Shreeya S Navale, Anwar Mulugeta, Ang Zhou, David J Llewellyn, Elina Hyppönen, Vitamin D and brain health: an observational and Mendelian randomization study, The American Journal of Clinical Nutrition, Volume 116, Issue 2, August 2022, Pages 531–540, https://doi.org/10.1093/ajcn/nqac107
4. Du Y, Liang F, Zhang L, Liu J, Dou H. Vitamin D Supplement for Prevention of Alzheimer’s Disease: A Systematic Review and Meta-Analysis. Am J Ther. 2020 Dec 26;28(6):e638-e648. PMID: 33395056. https://pubmed.ncbi.nlm.nih.gov/33395056/
