Vitamin D is essential for bone health … but what about brain health?
Evidence that vitamin D matters to your gray matter has grown fast over the past decade.
Worldwide, some 44 million people are diagnosed with dementia annually – a number expected to triple by 2050 as a result of rapid population ageing.
One billion people are thought to have low vitamin D levels, and research suggests that many – especially older adults – suffer poor bone, immune, or brain health as a result.
Many prior studies indicate that people with low vitamin D levels are more likely to experience cognitive problems … you'll find selected summaries in the Vitamin D & Brain Health
section of our news archive.
Clinical trials are required to confirm the findings from epidemiological studies, in which researchers compare people's vitamin D levels to their brain health.
In the meantime, the indications that robust levels of vitamin D help deter dementia just received major support from what may be the strongest epidemiological evidence collected to date.
The new study's results affirm the idea that vitamin D deficiency raises the risk of Alzheimer's disease and dementia quite dramatically.
Sophisticated study links low vitamin D levels to higher dementia risk
The new research was conducted by a team of global researchers, led by Dr. David Llewellyn at Britain's University of Exeter Medical School (Littlejohns TJ et al. 2014).
This large study was the first of its kind in which the dementia diagnoses were made by an expert multidisciplinary team using a wide range of measures, including brain imaging scans.
(The team included scientists from Columbia University, the University of Washington, the University of Pittsburgh, the University of Michigan, Florida International University, and Angers University Hospital in France.)
The subjects were 1,658 healthy Americans aged 65 and over from North Carolina, California, Maryland, and Pennsylvania, who were participating in a study probing causes of cardiovascular disease.
All of the subjects were free from dementia, cardiovascular disease, or stroke when the study got underway in 1992-1993.
Fish fit the vitamin D bill; Sockeye salmon stand out
In addition to getting vitamin D from supplements, certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.
Among fish, wild sockeye salmon rank as the richest source, with a single 3.5 ounce serving surpassing the US RDA of 600 IU by about 15 percent:
Vitamin D per 3.5 ounce serving*
Sockeye Salmon 687 IU
Albacore Tuna 544 IU
Silver Salmon 430 IU
King Salmon 236 IU
Sardines 222 IU
Sablefish 169 IU
Halibut 162 IU
*Click here for our full test results .
The researchers compared the participants' vitamin D levels at the outset of the study to their brain health status almost six years later.
And the striking results showed that those who were severely vitamin D deficient were more than twice as likely to develop some form of dementia, including Alzheimer's disease.
Those who were moderately deficient in vitamin D were 53 percent more likely to develop dementia … and those who were severely deficient were 125 percent more likely to develop dementia.
What about Alzheimer's disease, which is the most common cause of dementia?
The volunteers who were moderately deficient were 69 percent more likely to develop Alzheimer's, while the severely deficient group were 122 percent more likely to be diagnosed with Alzheimer's.
The study also found that a participant's risk of developing dementia increased when his or her vitamin D levels were below 50 nmol/L – the same thing as 20 ng/mL – at the outset of the study.
To put that blood level into perspective, many doctors and researchers recommend maintain a blood level of 75 nmol/L (i.e., 30 ng/mL) or more, based on evidence that this level is associated with lower risk of major diseases.
Leading vitamin D researcher Michael F. Holick, Ph.D., M.D., of Boston University Medical Center says the evidence supports keeping vitamin D levels above 30 ng/mL.
And Professor Holick notes that levels up to 100 ng/mL are “perfectly safe” … unless you have an uncommon disease called sarcoidosis, which often raises vitamin D levels in the body.
Size of the effect was unexpected
Dr. Llewellyn expressed surprise at the size of the risk from low vitamin D levels.
As he said, “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.” (UE 2014)
And he stressed the need for clinical evidence:
“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.
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.” (UE 2014)
Ensuring adequate vitamin D
Vitamin D comes from exposure to sunlight, fatty fish, and supplements. This explains why some call vitamin D the “seafood and sunshine nutrient”.
Fatty fish such as wild salmon, tuna, sardines, and mackerel, are the richest food sources, by far (see our sidebar, “Fish fit the vitamin D bill; Sockeye salmon stand out”).
Older people's skin can be less efficient at converting sunlight into vitamin D, making them more likely to be deficient and reliant on other sources. Just 15 to 30 minutes of strong midday sunshine is enough to boost your vitamin D levels substantially.
But numerous studies show that sun exposure is not a reliable vitamin D source for people in temperate climates. In many non-tropical places, the amount of UV radiation in winter, late fall, and early spring is too low – or people are wearing too much clothing – to generate much vitamin D in the body.
In addition to judicious sun exposure, it makes sense to take vitamin D3 supplements and eat plenty of fatty fish, such as wild salmon, tuna, sardines, mackerel, and herring.
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Annweiler C, Rolland Y, Schott AM, Blain H, Vellas B, Herrmann FR, Beauchet O. Higher Vitamin D Dietary Intake Is Associated With Lower Risk of Alzheimer's Disease: A 7-Year Follow-up. J Gerontol A Biol Sci Med Sci. 2012 Apr 13. [Epub ahead of print]
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Kendrick J, Targher G, Smits G, Chonchol M. 25-Hydroxyvitamin D deficiency is independently associated with cardiovascular disease in the Third National Health and Nutrition Examination Survey. Atherosclerosis. 2009 Jul;205(1):255-60. Epub 2008 Nov 11.
Littlejohns TJ, Henley WE, Lang IA, Annweiler C, Beauchet O, Chaves PH, Fried L, Kestenbaum BR, Kuller LH, Langa KM, Lopez OL, Kos K, Soni M, Llewellyn DJ. Vitamin D and the risk of dementia and Alzheimer disease. Neurology. 2014 Aug 6. pii: 10.1212/WNL.0000000000000755. [Epub ahead of print]
Slinin Y, Paudel M, Taylor BC, Ishani A, Rossom R, Yaffe K, Blackwell T, Lui LY, Hochberg M, Ensrud KE; for the Study of Osteoporotic Fractures Research Group. Association Between Serum 25(OH) Vitamin D and the Risk of Cognitive Decline in Older Women. J Gerontol A Biol Sci Med Sci. 2012 Mar 27. [Epub ahead of print]
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University of Exeter (UE). Link between vitamin D and dementia risk confirmed. August 6, 2014. Accessed at http://www.exeter.ac.uk/news/research/title_405559_en.html