The Surprising Benefits of Vitamin D for Brain Health

Why Sun Exposure Matters

While we're generally encouraged to be cautious about sun exposure, the evidence shows that, on balance, it's good for us. One well-known mechanism is related to sunlight's capacity to generate vitamin D in the skin. This vitamin appears to be beneficial for a range of things, including bone health, immunity, and cancer protection.

The Link Between Vitamin D and Cognitive Function

Evidence published in 2023 found that in a group of older adults, higher concentrations of vitamin D measured in brain tissue at autopsy were related to a 25-33% lower risk of dementia or its lesser forerunner, known as 'mild cognitive impairment' [1]. Interestingly, this same study found no significant link between brain vitamin D and the underlying neuropathology. For example, the build-up of damaged proteins characteristic of Alzheimer’s disease. This should remind us that these relationships are not straightforward.

So-called 'epidemiological' studies of this nature may be useful for finding associations and forming what are called 'hypotheses.' However, they generally cannot provide a 'causal' link between two things. Higher vitamin D levels may actually reduce the risk of cognitive impairment, or they may simply be associated with a reduced risk. In the latter case, perhaps people who are less cognitively impaired are more likely to spend time outdoors, thereby having higher vitamin D levels.

New Insights into Vitamin D's Protective Mechanisms

A recently published study sheds some light (excuse the pun) on the mechanisms by which vitamin D may be protective for the brain [2]. This review examined different lines of evidence and didn't just focus on cognitive impairment but also on other neurological issues such as multiple sclerosis, depression, autism, and ADHD. Across a range of conditions, lower vitamin D levels were found to be associated with increased risk. Again, 'correlation does not prove causation.'

This paper pointed out that brain cells in several parts of the brain have vitamin D receptors (VDRs). That doesn't prove a causal role, but it does establish the biological plausibility for one. The brain is clearly equipped to respond to vitamin D directly.

The Anti-Inflammatory Effects of Vitamin D

In addition, vitamin D has anti-inflammatory effects. There is evidence that inflammation can be an underlying process in conditions including cognitive decline, depression, and multiple sclerosis. This suggests that vitamin D could play a role in mitigating these issues.

Supporting Brain Cell Health

Vitamin D has also, in preclinical research, been shown to increase the production of 'brain-derived neurotrophic factor' (BDNF) and 'nerve growth factor' (NGF). These two substances support brain cell health. BDNF is closely tied to ‘synaptic plasticity,’ the process underlying learning and memory. NGF plays a role in keeping neurons alive and supporting their growth. Whether this translates into measurable benefits in humans is still unknown.

Conclusion: A Balanced Approach to Sun Exposure

All the evidence is not in. But what we do have, I think, is enough to suggest that vitamin D has broad benefits for the brain. Sunburn is to be avoided, but prudent sun exposure when the sun is high in the sky (the condition when vitamin D can be made in the skin) may be a low-friction way to help preserve our mental faculties as we age.

References:

1. Shea MK, et al. Brain vitamin D forms, cognitive decline, and neuropathology in community-dwelling older adults. Alzheimer's Dement. 2023; 19: 2389–2396.

   
   

2. Barakat G, et al. Vitamin D and brain health: A systematic review. Clinical Nutrition Open Science, 2026; 67.