In recent years there has been an increasing number of studies pointing towards the importance of Vitamin D in human health. Many conditions have been linked to Vitamin D deficiency, including neurodegenerative diseases such as Multiple sclerosis and Dementia.
Vitamin D is an essential nutrient that our bodies require to function normally. We can produce Vitamin D or absorb it through our diet. Around 90% of Vitamin D is produced in the skin from 7-Dehydrocholesterol as a reaction to sunlight. The production of Vitamin D can be limited by being at a higher latitude (i.e. closer to the poles), covering of skin, lack of outdoor activities, sunscreen use, old age, dark skin pigmentation and female sex. It is estimated that approximately 1 billion people worldwide have inadequate Vitamin D levels, mainly due to a lack of sunlight exposure. Nutrition is another important source of Vitamin D, especially when exposure to sunlight is reduced. Foods high in Vitamin D include fatty fish or Vitamin D fortified foods.
A number of recent cross-sectional studies suggest that low levels of Vitamin D may be associated with an increased risk of developing Alzheimer’s disease or other dementias. Vitamin D has various roles including the regulation of calcium homeostasis, beta amyloid deposition, antioxidant and anti-inflammatory properties, and potentially providing protection against neurodegenerative processes.
Although some physiological mechanisms have been suggested, we have not yet determined the exact role Vitamin D plays in the brain. Animal studies suggest that a lack of Vitamin D may impair the functioning of neurons. A study by Eyles and colleagues shows that the Vitamin D3 receptor is widespread in the brain. Using staining techniques, the researchers were able to show that the Vitamin D3 receptor and its connected enzyme had the strongest presence in the hypothalamus and in large neurons of the substantia nigra. Based on the distribution of this receptor it is thought that Vitamin D may act in a similar way to neurosteroids.
A meta-analysis of studies by Sommer and colleagues (2017), which analyzed data from 18639 participants, showed that people with a serious lack of Vitamin have a statistically significantly higher relative risk of 1.54 to develop dementia compared to people with sufficient Vitamin D. However, the quality of this evidence is very low, because many of the studies included were observational in nature, and often important confounding variables were not considered.
Research so far has only indicated that Vitamin D deficiency may be associated with dementia risk. No studies have established a causal link between the two. Future research needs to focus on environmental risk factors, such as Vitamin D, and establish what contributions if any these may have. This is particularly important as one third of dementia remains unexplained, and it is thought that these environmental risk factor could potentially play a pivotal role. Some of the key questions we need to answer include: Can Vitamin D supplements mitigate the risk of developing Dementia? And if yes, at which stage in life would they have to be introduced?
Vitamin D certainly does seem to play a key role in our health. It remains to be seen how exactly this “Wunderkind” of a nutrient will alter the landscape of dementia research.