Effects of High Dose Vitamin D Supplementation on Cognitive Functions

Vitamin D and its Importance

Vitamin D is an essential vitamin which is commonly abundant in common foods such as fish and egg yolks. Sunlight is also an excellent source of vitamin D. This vitamin serves several important functions in the body, one of which is keeping different muscle groups healthy. Besides, it helps the body maintain healthy teeth and bones. Finally, it reduces the risk of a weakened immune system.^[1] That said deficiencies in vitamin D raise the risks of cancers, bone deformities, and a weakened immune system.

The Link Between Vitamin D and Cognitive Functioning

Insufficient amounts of 25-hydroxyvitamin [25(OH)D] have always been associated with both the decline of cognitive functioning and dementia. Deficient 25(OH)D in the body has also been connected to the development of Alzheimer's disease.^[1] However, the effects of supplementing this vitamin in the body on cognitive functioning have always remained unclear. This lack of clarity prompted Jacqueline Pettersen to attempt pointing out the link that exists between nutrition and cognitive functions. Pettersen works at the University of Northern British Columbia as a neurologist. The researcher, therefore, came up with a hypothesis that it is possible to enhance cognitive functioning through high dose Vitamin D3 supplementation. According to the neurologist's hypothesis, this is especially the case among adults with insufficient 25-hydroxyvitamin D levels in their bodies, typically below 75 nmol/L.^[1]

The Study on Vitamin D Supplementation and Cognitive Performance

The study involved a healthy group of 82 adults residing in British Columbia, Canada which lies on the 540 North latitude. The adults, whose 25(OH)D levels at the beginning of the study were equal to or below 100 nmol/L, were selected at random and blinded to two different doses of vitamin D3; one of which was a High Dose and the other one a Low Dose. The High Dose had a potency of 4000 IU/d while the Low Dose had a potency of 400 IU/d.^[2] The supplementation program lasted 18 weeks, with the volunteers receiving regular vitamin D supplementation depending on the dose assigned to each of them. The researches then assessed baseline and follow-up serum 25(OH)D and cognitive performance. Under cognitive performance, they conducted several cognitive tests including verbal fluency, digital span, Symbol Digit Modalities Test, and the CANTAB® computerized battery.^[2]

Results of the Study

Upon evaluation of the results, the researchers noted no substantial baseline differences between the two groups. However, several differences arose between these dose groups. First and foremost, serum 25(OH)D increased substantially more in the High Dose class as opposed to their Low Dose counterparts. In the High Dose group, it rose from 67.2 ± 20 nmol/L to 130.6 ± 26 nmol/L and from 60.5 ± 22 nmol/L to 85.9 ± 16 nmol/L in the Low Dose group. Additionally, the results of the Pattern Recognition Memory task (PRM) revealed improved performance in the High Dose category on nonverbal memory (from 84.1 ± 14.9 to 88.3 ± 13.2, p = 0.043 (d = 0.3)). These two aspects of performance, however, did not increase in the Low Dose category.^[2]

Moreover, the assessment of the Pattern Recognition Memory task (PRM) revealed an increase in performance from 84.1 ± 14.9 to 88.3 ± 13.2, p = 0.043 (d = 0.3). The number of stages completed in the Paired Associated Learning task (PAL) also increased from 4.86 ± 0.35 to 4.95 ± 0.22, p = 0.044 (d = 0.5).^[2]

Greater Cognitive Improvement with High Dose Vitamin D Supplementation

Finally, the degree of cognitive improvement as assessed by the mixed effects modelling control for education, age, sex, and baseline performance revealed a greater extent of improvement in the High Dose group for these functions: PRM, p = 0.11 (d = 0.4), PAL, p = 0.058 (d = 0.4). Among the individuals whose 25(OH)D levels were below 75 nmol/L at the starting point, the High Dose group improved substantially and to a relatively greater extent on the PRM task (p = 0.025, d = 0.6).^[2]

Conclusion and Future Studies

From the results, it is evident that relatively high doses of vitamin D supplementation impact nonverbal memory positively. This is especially the case among people whose levels are below 75 nmol/L. Verbal memory and other cognitive domains, however, do not change due to the high supplementation doses. These findings are only preliminary. They are, however, in line with recent studies whose results showed major positive links between the levels of 25(OH)D and nonverbal memory, but not verbal memory. As such, higher levels of 25(OH)D are essential to better cognitive functioning; especially, visual memory.^[2]

However, it remains unknown whether vitamin D supplementation can delay the development or prevent dementia and age-related cognitive decline. The optimum levels of vitamin D that can improve cognitive functioning are still unknown and likely varies between persons, and this implies that it is imperative to conduct further studies concerning this topic.^[1][2] Pettersen's research team is currently evaluating the influence of underlying genetics, an excellent example being vitamin D receptor polymorphisms, and the impact of co-factors. This stems from the belief that vitamin D works in tandem with several nutrients to fulfill its purpose in the body.^[2]

Sources:

[1]

Fiera, N. (2017). Brain-boosting Vitamins. Retrieved from https://www.future-science.com/btn/news/jul17/24

[2]

Pettersen, J. A. (2017). Does high dose vitamin D supplementation enhance cognition?: A randomized trial in healthy adults. Experimental gerontology, 90, 90-97.