Vitamin D is the mis-named and oft misunderstood contributor to brain health that might be the easiest for any individual to address. Step outside into the sunshine. No really, it’s that easy. What’s that? It’s the middle of winter or you fear cancer? Alright, take a D3 supplement. And if you do either, you will increase your chances of avoiding Alzheimer’s.
The discovery of vitamin D started with a childhood disease caused by its absence. English children were suffering from rickets in the late 1800s and because they couldn’t yet blame television or video games, the authorities were stumped. It wasn’t until 1918 that they discovered they could
torture cure the children with cod liver oil (a good source of D3 compounds).
In 1922, the active form was isolated and since if followed the discovery of vitamins A, B, and C it was named vitamin D. note: While we still call it a “vitamin” D it is now considered a major steroid hormone.
In 1924 researchers discovered that the ultraviolet rays from sunlight are a major source of vitamin D. Modern estimates of our sources of vitamin D place UVB rays from sunlight as the source of 80% and dietary intake as the other 20%.
Vitamin D exists as D1, D2, D3, D4 and D5. The forms D2 and 3 are the most important forms used by the body, but studies have shown D3 to be more quickly converted to an active form in the body. D3 is also much better at raising D concentration in the body and at storing vitamin D in the body where it is stored in fat and in the liver. Also it should be noted that some studies indicate that D2 does not bind as well with the Vitamin D-binding protein (DBP) in our blood, further decreasing its effectiveness. While other studies are less critical of D2, there does not appear to be any debate about the effectiveness of D3 as a supplement.
From Rickets to Alzheimer’s
University of Exeter, 2014 “Vitamin D and the risk of dementia and Alzheimer disease” published by the American Academy of Neurology. Using the Cardiovascular Health Study (CHS), which gathered data from thousands of participants over the age of 65 from four different locations in the U.S., the Exeter researchers focused on 1,658 elderly individuals without dementia, stroke or cardiovascular disease to see if vitamin D concentrations are associated with an increased risk for Alzheimer’s.
Those participants in the study with the lowest levels of vitamin D in their blood had a substantially higher risk of developing Alzheimer’s and all other forms of dementia.
The CHS started with over 5,000 adults in 1989–1990. Participants were given extensive blood test, MRI scans, and cognitive evaluations. The mean follow-up in the CHS was 5.6 years. The Exeter researchers whittled their total study size down by excluding those participants that started the study with evidence of cardiovascular disease or stroke, those without a determination of vitamin D levels, and those without a dementia status. This resulted in a final sample of 1,658.
To better insure that their final measurements were on the effects of vitamin D they adjusted for variable that have been shown to correlate with Alzheimer’s such as education status, sex, season of blood collection (spring, summer, winter, fall), body mass index, smoking, alcohol consumption, and significant depressive symptoms. If the results were different I might break down how some of those variables were defined, but in this case it will not be necessary.
It will be useful, however, to define the three levels of vitamin D in the blood (serum levels). Severely Deficient was defined as below 25 nmol/L; Deficient was 25-50 nmol/L; and above 50 nmol/L was defined as Sufficient.
After the first round showed positive associations between serum levels of vitamin D and Alzheimer’s, they repeated the analysis to include health conditions identified as potential mediators such as diabetes, and hypertension. They also considered ethnicity, and socioeconomic status. The researchers also excluded any participants who developed dementia within the first year as these so called “early converters” can cloud the association between variables.
Over the 5.6 years between baseline testing and follow-up 171 participants developed dementia (of the 1,658), including 102 cases of Alzheimer’s. The risk of all-cause dementia and Alzheimer’s markedly increased below a threshold of 50 nmol/L.
In the first analysis those below 50 nmol/L (Deficient) had about a 51% increased risk of all-cause dementia and Alzheimer’s. Those who were below 25 nmol/L (Severely Deficient) had about a 122% increase in risk for both.
The second analysis adjusting for potential confounders did not alter the pattern of results. In fact, there was a linear trend across groups in all analyses, suggesting a very strong correlation. Further statistical modeling suggests that the risk of all-cause dementia and Alzheimer’s increases dramatically if vitamin D concentrations are below 50 nmol/L.
There were no significant interactions from any of the variables the researchers had identified as potential confounding factors such as age, sex, health conditions, ethnicity, and socioeconomic status, etc. That pretty much translates to “anyone and everyone can benefit from having a sufficient level of vitamin D.”
Why This Association May Exist
Both the vitamin D3 receptor and the enzyme responsible for synthesizing the bioactive form of vitamin D, are found throughout the human brain and they must be there for a reason. One possible reason is the clearing of amyloid plagues, which vitamin D encourages in vitro (in a test tube). It has also been shown to reduce amyloid-induced cytotoxicity and apoptosis (cell death) in primary cortical neurons.
Vitamin D deficiency has been linked to vascular dysfunction and ischemic stroke risk, which would explain why sufficient levels of vitamin D protected against all forms of dementia and not just Alzheimer’s.
This study found that the neuroprotective effects of vitamin D ceased to increase above 50 nmol/L. In other words, at 50 and above there were no more measurable positive effects, so inserting an IV of vitamin D and walking around all day is just going to make you look silly. However, there is nothing silly about levels below 50 as they correlate with increased risk of all forms of dementia and with Alzheimer’s.