Written by Taylor Woosley, Staff Writer. This study suggests that higher levels of dietary vitamin D intake, serum total 25(OH)D, and 25(OH)D3 resulted in improved cognitive performance in subjects aged 60 years and older.
Life expectancy has seen an increase throughout the 20th century. One major challenge with longer living humans is the prevalence of cognitive decline in the elderly 1. A major public health crisis is the advancement of neurological disorders such as dementia and Alzheimer’s disease (AD). An estimated 25 million people suffer from dementia and projections show that around 5 million people a year are diagnosed 2. Proper dietary habits such as vitamin D intake may play a role in controlling or delaying cognitive decline. Vitamin D plays a role in the function of over 200 genes and its neuro-protective and anti-inflammatory properties promote brain health 3. Numerous studies have shown the importance of vitamin D on nervous system function and its ability to pass the blood-brain barrier through passive diffusion 4. Few studies have examined the dose-response relationships between dietary vitamin D intake, serum total 25(OH)D, serum 25(OH)D2, and serum 25(OH)D3 and their effect on cognitive performance in elderly Americans.
In this study, Wang et al examined data gathered from the National Health and Nutrition Examination Survey (NHANES) from two separate cycles, 2011-2012 and 2013-2014. The NHANES’ cognitive performance data was collected through the Consortium to Establish a Registry for Alzheimer’s disease (CERAD). The CERAD test consists of a Word Learning sub-test, the Animal Fluency test and the Digit Symbol Substitution Test (DSST). These tests were designed to asses a person’s ability to learn new verbal information, examine verbal fluency, and assess how quickly someone can process and recall information.
A total of 5,259 participants of NHANES 2011-2012 and 2013-2014 (≥60 years and ≥70 years) were included in this cross-sectional study. Participants were divided into two groups, the dietary vitamin D intake group (n=2524) and the serum vitamin D group (n=2735). Dietary vitamin D intake was assessed by two 24-hour recall interviews. The data was further analyzed and divided into two groups based on vitamin D intake regarding the vitamin D Recommended Nutrient Intakes (5.00 µg/d) from the Food and Agriculture Organization of the United States (FAO) and World Health Organization (WHO). Those with lower dietary vitamin D intakes than RNIs were used as a reference group (Q1: ≤5.00 µg/d) and those with dietary vitamin D intakes higher than RNIs were put into a second group (Q2: >5.00 µg/d). To assess 25(OH)D levels, participants had blood drawn after fasting for 9 hours. The concentration of serum 25(OH)D3 and 25(OH)D2 was analyzed using high-performance liquid chromatography (HPLC) tandem mass spectrometry. The sum of these levels resulted in the serum total 25(OH)D concentration (nmol/L). Participants were also divided into two groups based on their 25(OH)D2 concentration levels (Q1: ≤1.45 nmol/L and Q2: >1.45 nmol/L). Several factors (gender, race, BMI, smoking and drinking status, poverty-income ratio, education level and pre-existing conditions) were included as covariates. Time of season and level of physical activity was also considered and in the dietary vitamin D intake group total energy intake was another covariate.
The results were as follows:
- Comparison between the lowest dietary vitamin D intake group and the highest dietary vitamin D intake resulted in OR=0.51, 95% CI 0.36 to 0.72 for the Animal Fluency test score and OR=0.45, 95% CI 0.31 to 0.66 for the DSST score.
- The most significant effects on cognitive performance regarding DSST scores occurred when dietary vitamin D intake was higher than 20.75 µg/d in both men (OR=0.46, 95% CI 0.26 to 0.82) and women (OR=0.50, 95% CI 0.30 to 0.83).
- Serum total 25(OH)D concentration 86.30 nmol/L and higher resulted in statistically significant improvements in DSST test results (OR=0.68, 95% CI 0.47 to 0.97).
- Serum 25(OH)D3 concentrations higher than 80.63 nmol/L was associated with DSST scores (OR=0.62, 95% CI 0.44 to 0.86).
- There was no significant association when observing serum 25(OH)D2 and cognition scores.
Furthermore, the study data shows an L-shaped dose-response relationship between dietary vitamin D intake and the potential for low cognitive performance (the Animal Fluency test, P=0.426; DSST, P=0.239). Similar L-shaped dose-response results were associated with serum total 25(OH)D and the risk of low cognitive performance (DSST, P=0.697) along with serum 25(OH)D3 (DSST, P=0.409).
Evidence from the current study supports the important role vitamin D plays regarding cognitive function. In conclusion, the data provided by Wang et al showcases that dietary vitamin D intake, serum total 25(OH)D, and 25(OH)D3 concentration were negatively associated with low cognitive performance risk. Additionally, linear L-shaped dose-response relationships between them were established and this study provides evidence that gender did not play a significant role in cognitive performance. Key study limitations pertain to the study being cross-sectional, meaning a cause and effect could not be determined. Another limitation revolves around the data of dietary vitamin D intake through a 24-hour dietary recall which does not accurately judge individual vitamin D intake and can result in recall bias. Lastly, limitations arise from dietary vitamin D intake and serum 25(OH)D being associated solely with cognitive performance assessed by DSST. Researchers state that future studies need to further clarify the relationship between dietary vitamin D intake, serum total 25(OH)D, 25(OH)D2, and 25(OH)D3 and their effects on cognitive performance.
Source: Wang, RuTong, Weijing Wang, Ping Hu, Ronghui Zhang, Xue Dong, and Dongfeng Zhang. “Association of Dietary Vitamin D Intake, Serum 25 (OH) D3, 25 (OH) D2 with Cognitive Performance in the Elderly.” Nutrients 13, no. 9 (2021): 3089.
© 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
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Posted November 22, 2021.
Taylor Woosley studied biology at Purdue University before becoming a 2016 graduate of Columbia College Chicago with a major in Writing. She currently resides in Glen Ellyn, IL.
References:
- Wang R, Wang W, Hu P, Zhang R, Dong X, Zhang D. Association of Dietary Vitamin D Intake, Serum 25 (OH) D3, 25 (OH) D2 with Cognitive Performance in the Elderly. Nutrients. 2021;13(9):3089.
- Landel V, Annweiler C, Millet P, Morello M, Féron F. Vitamin D, Cognition and Alzheimer’s Disease: The Therapeutic Benefit is in the D-Tails. Journal of Alzheimer’s disease : JAD. May 11 2016;53(2):419-44. doi:10.3233/jad-150943
- Naeem Z. Vitamin d deficiency- an ignored epidemic. Int J Health Sci (Qassim). Jan 2010;4(1):V-vi.
- Sultan S, Taimuri U, Basnan SA, et al. Low Vitamin D and Its Association with Cognitive Impairment and Dementia. J Aging Res. 2020;2020:6097820. doi:10.1155/2020/6097820.
