The Relationship between Vitamin D Intake and Cognitive Decline

Alzheimer’s disease is a form of dementia that is characterized by a progressive decline in cognitive abilities. It currently plagues over 37 million people worldwide and this number is expected to increase. Research showed that Vitamin D, a fat soluble hormone, plays a large role in neurodevelopment and therefore, impacts brain health and function. This study found that higher vitamin D intake is associated with a lower risk of developing Alzheimer’s in older women. In this cross-sectional study, researchers assessed the diets and cognitive status of women who were 75 years and older. There is no known cure to Alzheimer’s disease and therefore, it is important to evaluate any possible risk factors in order to access the health needs of a specific group. While this study provided information regarding cognitive function in older women, there are several limitations that must be discussed: the method of recruiting participants, the nature of data collection, and the issue of confounding and residual bias. By addressing and improving these limitations, the study will be able to strengthen the association between vitamin D intake and Alzheimer’s disease.

The first limitation in this study was due to the lack of representativeness of the general population. The cohort study was restricted to well functioning women with access to foods containing vitamin D. The EPIDOS study recruited 7,598 participants from 5 different French cities to study the risk factors for hip fractures in older women, those who were excluded included those who were not able to walk on their own, had a previous history of hip fracture or hip replacement, and were unable to comprehend or answer questionnaires. At the end of this four year study, 1,462 participants were invited to continue in a three year follow-up regarding vitamin D intake and cognitive function, known as the Toulouse cohort study. At the seventh year of follow-up, there were 498 women who fulfilled the cognitive status. The group of participants originally came from a prospective cohort study evaluating the risk factors of hip fractures and while they were screened for criteria for this study, the population should have been selected at random in order to lessen any selection bias and lack of representativeness. While the results from the study are true, they are only likely to apply to the group of women from those 5 French cities, rather that the larger population of the country. It is possible that the women from these cities were more affluent and therefore, had access to vitamin D rich foods. There were certain criteria that needed to be met in order to continue however, the participants seemed to be picked from convenience and the random sampling was also more focused on the EPIDOS study. Convenience sampling is a technique where participants are recruited based on their availability and willingness to engage in the study however, there is a higher risk of selection bias and sampling error which weakens the validity of the study. Sampling is necessary because it is impossible to study an entire population, however fair samples must be provided so that all population characteristics are being taken into account. Researchers can improve this study by randomly selecting French cities from different regions, ensuring their participants represent women who have access and those who do not have access to vitamin D rich foods.

In order to compare the cognitive status and vitamin D intake of these participants, they were required to complete self-administered food frequency questionnaires. According to researchers, the questionnaire consisted of 21 questions that inquired about their diet and were then used to compute their vitamin D intake. The way the data was collected introduced a few restrictions to the study. The first limitation in regards to data collection is unreliable and invalid data due to participants who are cognitively impaired. There are four steps to consider when answering questionnaires, this includes: comprehension of the question, ability to recall, retrieving the information, and communicating their answers accurately. Therefore, the cognitively impaired participants may have skewed the data which would affect the way researchers. One way to prevent any inaccurate responses would be to have the participants receive a hydroxy vitamin D blood test, which is one of the most accurate ways to measure vitamin D intake. Even with those who are cognitively able to answer these questionnaires, there is still a possibility that they may have answered inaccurately. This could be because the participants want to appear healthier than they are. Another possible reason is they want to give a response that will help or please the researchers. In order to prevent this, the study should switch to a less burdensome method such as personal, face to face interviews. This data collection method would not require any reading skills, lowering the cognitive burden for participants. The interview would also be able to increase response, maintain motivation to answer, clarify an unknown questions, and use memory jogging skills. However in this case, the interviewers would need to be thoroughly trained. By correcting the method of data collection, this will improve the efficacy of the study and minimize any possible bias.

This article analyzes the relationship between vitamin D dietary intake and cognitive ability in women 75 years and older. The results suggest that those with high Vitamin D intake are at lower risk for developing Alzheimer’s Disease. While this was one step closer towards reducing risk factors for Alzheimer’s, it was not entirely conclusive due to the lack of representativeness, burdensome questionnaires, and confounding and residual bias presented within the study. Improvements to tackle these limitations and improve the validity of the study include shifting the study design to a longitudinal study to include randomization, using face to face interviews, and to utilize multivariate analysis to control confounding and residual bias. If all of the limitations are taken into consideration and properly dealt with, the study would help us to better understand Alzheimer’s and to enhance the health of the general population.