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Vitamin D Deficiency Linked to Increased Risk of Alzheimer’s and Dementia

A new study conducted at the University of Exeter, UK, has shown that vitamin D deficiency is strongly linked to the development of Alzheimer disease and dementia.

The study looked at the blood concentrations of 25-hydroxyvitamin
D (25(OH)D), the biomarker for vitamin D, in 1,658 elderly Americans aged 65 and over (the average age was 73), who took part in the Cardiovascular Health Study. The subjects were followed for an average of 5.6 years to assess the development of Alzheimer’s disease and dementia.

Adults who were classed as having a moderate vitamin D deficiency, defined as having levels between 25 and 50 nmol/L (see below) were found to have a 53% increased risk of dementia of any kind. Those with severe vitamin D deficiency (less than 25 nmol/L) saw their risk increase to 125%.

Similarly, those with moderate deficiency were 69% more likely to develop Alzheimer’s with the risk jumping to 122% for the severely deficient.

The results stood even after taking into account the possibility of reverse causation, that Alzheimer’s and dementia might themselves through changes in diet, lifestyle etc  thus leading to lower serum levels of vitamin D, as well as factoring possible confounders, like smoking, alcohol, age and education that may also have some bearing on the development of dementia.

In a press release project leader, Dr David Llewellyn, stated

We expected to find an association between low Vitamin D levels and the risk of dementia and Alzheimer’s disease, but the results were surprising – we actually found that the association was twice as strong as we anticipated.

Clinical trials are now needed to establish whether eating foods such as oily fish or taking vitamin D supplements can delay or even prevent the onset of Alzheimer’s disease and dementia. We need to be cautious at this early stage and our latest results do not demonstrate that low vitamin D levels cause dementia. That said, our findings are very encouraging, and even if a small number of people could benefit, this would have enormous public health implications given the devastating and costly nature of dementia.

Something I often find surprising when reading through press releases and papers on vitamin D is the constant reference to supplements and diet to help raise the levels of vitamin D, when by far the most effective and efficient way to ensure adequate vitamin D levels is via exposure to sunlight, though of course location plays its part.

Dosage, concentration, mcg and nmol/L and IU's
The unit nmol/L refers to nanomoles per litre. The mole is a standard unit used in chemistry for measuring the amount of a chemical and nano refers 10-9 or 0.000000001 or simply a billionth.

To confuse things further other units are often used, nanogram per millilitre (ng/ml), micrograms (mcg, μg),  or the International Unit, IU.

1IU = 0.025 mcg, so 100IU = 2.5mcg

100 IU (2.5 mcg) per day increases vitamin D blood levels 1 ng/ml (2.5 nmol/L)

Converting ng/ml to nmol/L multiply by 2.5, so 30ng/ml, for example, would be 30×2.5=75nmol/L.

Conversely, to convert nmol/L to ng/ml you would divide by 2.5, so 100nmol/L is 100/2.5=40ng/ml. 

What’s sufficient?

There still seems to be plenty of debate about what constitutes sufficiency and deficiency for vitamin D with different organisations claiming different levels, the Vitamin D Council, for example, has levels of 0-30ng/ml as deficient, 31-39 ng/ml as insufficient and 40-80ng/ml as sufficient, the Endocrine Society has 0-20ng/ml, 21-29ng/ml and 30-100ng/ml as its respective levels.

The levels used in this particular study, set by the US Food and Nutrition Board, are much lower so it’s interesting to see that the level defined as sufficient here and deficient elsewhere still seems to act as some kind of threshold for brain health.

nmol/L ng/ml
Severe deficiency <25 10
Moderate deficiency ≥25-≤50 10-20
Sufficient ≥50 20


While further studies looking at diet and supplements are interesting, I can’t help but wonder about the role sunlight plays if vitamin D deficiency does, in fact, play a part in dementia and Alzheimer’s. Today more and more people slather on sunscreen and hide away from the sun. Here in Japan it’s common to see many women covering every millimetre of their skin in order to avoid the ‘damaging’ effects of the sun, yet few if any pay attention, or are maybe completely unaware of the possible benefits of getting more sun.

We have come to vilify sun exposure in the same way that we wrongly demonized saturated fat much to our detriment. Could the same be possible true for the sun?

It’s also interesting to see that this study drew upon data from the Cardiovascular Health Study as evidence also exists that suggests that sun exposure would not only raise vitamin D levels but have positive effects on the heart, too.

Watch Richard Weller’s TED Talk, Could the sun be good for your heart below

The full study was published in the online journal Neurology and can be accessed here.

Got a question or maybe something to add? Leave a comment and let me know!