Understanding Vitamin D Deficiency Effects on the Brain

Vitamin D helps regulate the amount of calcium and phosphate in the body, providing the nutrients needed to maintain the health of bones, teeth, and muscles. A deficiency in vitamin D can lead to reduced bone density and can contribute to osteoporosis and fractures. While the role of vitamin D in skeletal health is well-established, new research has linked vitamin D deficiency to a range of non-skeletal conditions, including cardiovascular disease, diabetes, stroke, and recently, cognitive impairment and dementia.

In this article, we will take a look at the potential effects of vitamin D deficiency on brain health, discussing its effects on the two primary components of brain health: cognitive health and mental and behavioral health. 

Vitamin D Deficiency Effects on Brain Health: Cognitive Health

Over the last several decades, animal studies and human studies have demonstrated a potential link between vitamin D deficiency and cognitive decline. While many cross-sectional studies have shown a strong association between low vitamin D and cognitive impairment, longitudinal studies have shown rather mixed results.

For example, a 2018 population-based longitudinal study of 1,058 adults (with a median age of 75) found that even moderately low vitamin D was associated with poorer performance in multiple domains of cognitive function. However, low vitamin D was not able to predict a 12-year cognitive decline.

On the other hand, a 2015 population-based longitudinal study of 405 elderly adults found that severe vitamin D deficiency was independently associated with future risk of mild cognitive impairment (MCI) as well as dementia. Similarly, a 2017 population-based longitudinal study of 916 adults aged 65+ found that compared to individuals with vitamin D sufficiency, those with vitamin D deficiency exhibited a faster rate of cognitive decline. Vitamin D deficiency was associated with a nearly three-fold increased risk of developing Alzheimer’s disease. 

While the underlying mechanisms linking vitamin D deficiency with cognitive decline and dementia are not fully understood, several mechanisms have been proposed:

• Vitamin D has shown neuroprotective effects on the brain, including the clearance of beta-amyloid plaques, a hallmark of Alzheimer’s disease. A lack of vitamin D may cause an increased buildup of such plaques due to the reduction in clearance, contributing to cognitive decline.
• Because lower levels of vitamin D are produced in the older population, a deficiency in vitamin D may be an accelerating factor in the progression of the aging process. In other words, vitamin D deficiency may accelerate age-related cognitive decline.
• Because vitamin D modulates the biosynthesis of neurotransmitters and neurotrophic factors, and its receptors are found in the central nervous system, vitamin D deficiency may be a risk factor for several neurodevelopmental and neurodegenerative disorders.

Vitamin D Deficiency Effects on Brain Health: Mental and Behavioral Health

Vitamin D deficiency has been increasingly associated with several depressive disorders, though the directionality remains unclear. While vitamin D deficiency is known to be more prevalent in those with depressive disorders, some researchers believe that low vitamin D levels may increase the risk of developing depression.

Several cross-sectional studies and cohort studies have linked depression and low levels of vitamin D. In a 2020 systematic review of available literature, it was found that all included studies demonstrated that depressed subjects had lower levels of vitamin D compared to controls. They also found that those with the lowest vitamin D levels had the greatest risk of depression (odds ratio 1.31).

Proposed biological links between vitamin D and depression include:

• Immunomodulation
• Inflammation
• Cellular signaling
• The hypothalamo-pituitary-adrenocortical (HPA) axis
• Intracellular calcium homeostasis
• Monoamine neurotransmission

Emerging research also suggests that vitamin D supplementation may provide therapeutic benefits for individuals with depression; however, findings have been somewhat inconsistent.

How to Increase Your Vitamin D Levels

According to the Office of Dietary Supplements at the National Institutes of Health recommended that daily allowances for vitamin D are as follows:

* Adequate intake

An estimated 41.6% of Americans have a vitamin D deficiency. Given the high prevalence, research surrounding the effects of vitamin D deficiency on brain health may have important public health implications, though further investigation is needed.

If you are looking to increase your vitamin D levels to meet the recommended daily intake, you may consider the following sources of vitamin D:

• Certain foods: While few foods naturally contain vitamin D, fatty fish (e.g. mackerel, trout, salmon, and tuna) and fish oils are a good way to boost your vitamin D levels. Egg yolks, cheese, and beef liver contain small amounts of vitamin D.
• Sun exposure: Most people can make enough vitamin D needed to meet the above requirements through exposure to sunlight. The energy from the sun transforms a chemical in your skin into vitamin D₃. It is then carried to the liver and finally to the kidneys, where it is turned into active vitamin D.
• Dietary supplements: Dietary supplements are another source of vitamin D and can be a good option in winter months or in locations that do not receive as much sunlight.