Vitamin D is crucial for building healthy bones and a strong immune system, but not getting enough could lead to several conditions—including diabetes, high blood pressure and falls in older people. And now, research published in The American Journal of Clinical Nutrition is suggesting a vitamin D deficiency could also be linked to a higher risk for dementia and stroke.
“Vitamin D deficiency was associated with lower brain volumes and an increased risk of dementia and stroke,” Elina Hyppönen, the study’s lead author and director of the University of South Australia’s Australian Centre for Precision Health, told SeniorsMatter. “Reduced brain volumes can be a sign of neurocognitive disease and could indicate a higher dementia risk later in life.”
Hyppönen and her colleagues analyzed genetic data from almost 295,000 participants from the UK Biobank, a biomedical database containing health information from half a million UK participants.
In the study, the researchers grouped the participants with higher or lower vitamin D levels based on their genes and looked at how this was associated with their risk of developing dementia.
“If there is a true effect of vitamin D on dementia risk, then this type of genetic analysis should also provide evidence for this, and this is exactly what we saw,” Hyppönen said.
Furthermore, they were also able to look at how this type of genetic advantage – where people would always have slightly higher vitamin D levels than others – is associated with dementia risk when vitamin D concentrations are very low.
“We were able to show that the effect that vitamin D has on dementia risk is much stronger and potentially restricted to those people whose concentrations are very low—suggesting that efforts to increase concentrations are only going to help if you are vitamin D-deficient,” she added.
The study concluded that participants with vitamin D levels below 25 nanomoles per liter (nmol/L) were predicted to be 54% more prone to dementia than participants with higher levels (50 nmol/L).
The scientists noted that further research is needed to better understand the effects of vitamin D on dementia and stroke and other health outcomes.
Why does a lack of vitamin D increase the risk of dementia and stroke?
According to Hyppönen, vitamin D may have several effects on the brain, including a protective effect on the hypothalamus, which produces hormones that control heart rate, mood and body temperature.
She said when active vitamin D is present in the hypothalamus, it can help promote the growth and maturation of neurons and brain cells because there are vitamin D receptors in the hypothalamus as well.
In addition, there may be vascular mechanisms involved, as active vitamin D has been associated with reduced thrombosis (blood clotting), said Scott Kaiser, MD, geriatrician and director of Geriatric Cognitive Health for the Pacific Neuroscience Institute at Providence Saint John’s Health Center.
“Not only does vitamin D have an impact on brain cell growth and health, but it can also potentially have impacts on the health of our blood vessels, including less thrombosis, which would be a reduction of destructive blood clots either in large vessels or small vessels,” he said.
Hyppönen added vitamin D also has been associated with the regulation of the renin-angiotensin system, which can affect blood pressure.
Lastly, vitamin D can have anti-inflammatory effects, which may support brain health by reducing inflammation related to neurovascular damage and possibly reducing amyloid proteins, (commonly observed in Alzheimer’s disease).
How much vitamin D do I need daily?
For adults between 19 to 70, the National Institutes of Health recommends 15 micrograms (mcg) or 600 international units (IU), and adults 71 and older should have 20 mcg or 800 IU daily.
“It’s important to try and make sure that none of us are vitamin D-deficient,” Hyppönen said. “There is no need to use high doses, just the typical supplements supporting government guidelines should be enough for most people.”
However, if someone exceeds the recommended daily dose – typically through supplements and not by diet or sun exposure – it can cause vitamin D toxicity, a buildup of calcium in the blood that can lead to nausea, vomiting and weakness, and might progress to bone pain or kidney problems. Just be sure to check with your health care provider for recommendations and to test your levels, said Mona Rasi, CNP, NNCP, a nutritionist and natural nutrition clinical practitioner.
“Everybody is different, and everyone must check their vitamin D levels before taking it in a supplement form,” Rasi added. “According to this study, vitamin D toxicity can result in many health issues; however, getting vitamin D from diet and sun exposure is unlikely to cause toxicity.”
Are there alternative ways to get vitamin D?
Besides supplements, Kaiser said there are other ways to get vitamin D to support bone and brain health, including from ultraviolet light like the sun. If people decide to get vitamin D naturally from sunlight, Kaiser recommends you consider your own risk for skin cancer and use appropriate sunscreens.
Rasi added there are some foods you can eat that naturally contain vitamin D, such as fatty fish (salmon, tuna, sardines and mackerel), beef liver, cheese, mushrooms and egg yolks. There are also beverages with added vitamin D, including milk, orange juice and other dairy products.
Other steps to prevent the risk of dementia and stroke
Beyond meeting the recommended amount of vitamin D daily, take additional steps to prevent the risk of dementia and stroke:
- Eat a balanced and healthy diet and focus on anti-inflammatory whole foods
- Maintain a healthy weight
- Move and exercise regularly
- Avoid smoking
- Limit alcohol intake