Researchers from Qingdao, China, have identified L-shaped dose-response relationships between three markers of vitamin D status and cognitive performance in the elderly. This hadn’t been explored previously and has enabled the scientists to propose referable values of dietary vitamin D intake, serum 25-hydroxyvitamin D3 (25(OH)D3) and total 25-hydroxyvitamin (25(OH)D) for protecting cognitive performance.
“The study found that dietary vitamin D intake, serum total 25(OH)D and 25(OH)D3 concentration were negatively associated with low cognitive performance and risk, and linear L-shaped dose-response relationships between them were identified,” wrote the researchers, in the journal Nutrients.
Dementia: a growing global challenge
As life expectancy increases, cognitive performance decline in the elderly has become a major global public health challenge. According to the WHO, the number of people living with dementia is expected to triple to 152 million by 2050. As vitamin D is neuroprotective, anti-inflammatory and antioxidant, it is considered to be one of the protective factors for cognitive performance.
Dietary vitamin D intake and serum 25-hydroxyvitamin D (25(OH)D) are commonly used to assess vitamin D status. Several studies have looked at the relationships between vitamin D intake and serum 25(OH)D on cognition, but the association remains controversial. Moreover, the dose-response relationship has not been explored - an area that is important to understand as the varying chemical construction and physiological activities of these vitamin D markers might have different effects on cognition.
This knowledge gap prompted the scientists to investigate the association and dose-response relationships of dietary vitamin D intake, serum total 25(OH)D, serum 25(OH)D2 and serum 25(OH)D3 with cognitive performance.
2011-2014 data from the National Health and Nutrition Examination Survey (NHANES) was used as the basis of the study. Just under 20,000 Americans were originally included in the survey, but after excluding the under 60s and other participants who didn’t meet eligibility criteria, the researchers were left with 2425 participants with dietary vitamin D intake data and 2735 participants with serum 25(OH)D measures.
The database contained cognitive performance data that were obtained to establish a Registry for Alzheimer’s Diseases (CERAD) World Learning sub-test, Animal Fluency test and Digital Symbol Substitution Test (DSST). A binary regression model was applied to evaluate the association between vitamin D and cognitive performance and restricted cubic spline model was adopted to evaluate the dose-response relationship.
RNIs for cognitive performance?
L-shaped dose-response relationships were found between three of the vitamin D status markers (dietary vitamin D, serum total 25(OH)D and serum 25(OH)D3) and cognition.
Evaluating the dose-response relationship allowed the scientists to pinpoint the vitamin D levels that were associated with the most significant effects. These results showed that RNIs (Reference Nutrient Intakes) are preferable for protecting cognitive performance, said the researchers.
Referable values of serum total 25(OH)D, 25(OH)D3 concentration and dietary vitamin intake were proposed, which the researchers said need to be researched by further studies.
For the Animal Fluency Test, dietary vitamin D intake higher than 20 μg/d was associated with a reduced risk of low cognitive performance, whilst for the DSST, the risk of low cognitive performance began to decrease when dietary vitamin D intake was higher than 4 μg/d. When serum total 25(OH)D concentration was higher than 87 nmol/L and serum 25(OH)D3 concentration was higher than 44 nmol/L, both were associated with the decreased risk of low cognitive performance in DSST. However, this association was not found between serum 25(OH)D2 and cognitive test scores.
“The relationship between serum 25(OH)D2, 25(OH)D3 and cognition has not been explored in past studies. In our study we found that higher 25(OH)D3 concentrations had a protective effect on cognitive performance, while the association between 25(OH)D2 was not significant,” wrote the researchers.
With regard to the mechanism, they said several studies have shown that vitamin D affects cognitive performance by affecting cell differentiation, neurotransmitter synthesis and the expression of genes and proteins involved in neural structure.
“These action mechanisms emphasise the important role of vitamin D in brain function, so we think vitamin D may be an important nutrient for maintaining better cognitive performance and preventing cognitive decline in the elderly,” they wrote.
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”