By Craig Weatherby
Vitamin D holds promise – yet unproven – as a deterrent to dementia.
Epidemiological studies almost uniformly link low vitamin D levels to the presence of Alzheimer's … or greater risk of developing this common kind of dementia.
And as French researchers noted, this apparent link is biologically plausible: “… vitamin D simultaneously targets several factors leading to neurodegeneration [and dementia] …” (Annweiler C et al. 2010)
They cited the hormone-like vitamin’s healthy influences on a variety of processes affecting brain health:
Help avoid thyroid problems.
Help maintain blood flow in the brain.
Support the body’s inflammation/oxidation control systems.
Support growth and survival and maintenance of neurons (brain cells).
Help maintain healthy levels of the key neurotransmitter called acetylcholine.
Help clear the pro-inflammatory amyloid beta plaque associated with Alzheimer's disease.
For sure, we need clinical trials to test whether vitamin D supplements – or diets high in fatty fish, which are its only good food source – can reduce the risk of dementia.
In the meantime, evidence linking lack of the “sunshine-and-seafood” vitamin to Alzheimer's disease (AD) continues to accumulate.
Most recently, scientists from two British academic centers – Kingston University and Brighton and Sussex Medical School – uncovered more evidence linking Alzheimer's to a lack of vitamin D (Shah I et al. 2012).
British study links vitamin D lack to Alzheimer’s
As lead researcher Declan Naughton said, his team came up with some novel findings about the different forms of vitamin D.
“There are several different types of vitamin D that can be active in the body … a blood test, which we developed at Kingston University, was for the first time able to accurately measure which, if any, of the different variations of vitamin D were present in Alzheimer's patients.” (KU 2012)
The Kingston-led scientists analyzed blood samples from three groups:
Controls free of dementia
Un-medicated Alzheimer's patients
Medicated Alzheimer's patients taking standard AD drugs
They measured the participants’ total vitamin D levels and the levels of the two forms of vitamin D obtainable from foods or supplements … vitamin D3 and vitamin D2:
Vitamin D3 is made in the skin following exposure to sunlight (UVB) and fatty fish are the only good food sources (see our sidebar, “Fish fit the vitamin D bill”).
Vitamin D2 is even rarer in foods, with low levels found mostly in fungi (yeast and mushrooms), and higher levels (e.g., 100 IU per serving) added to some fortified foods (milk, yogurt, etc.).
As seen in other studies, the overall vitamin D levels and vitamin D3 levels in the Alzheimer's patients were lower than in the healthy controls.
And the UK team found that the un-medicated Alzheimer's patients had very low levels of vitamin D2.
As professor Naughton said, “The vitamin [D2] was either non-existent or in such low quantities that it could barely be measured. In comparison, people in the study who were either being treated with drugs to control their Alzheimer’s or who didn't have the condition at all showed far higher levels.” (KU 2012)
Vitamin D2 conversion seen as potential problem
As we said, there’s ample if inconclusive evidence that lack of vitamin D might promote the development of Alzheimer's.
However, according to professor Naughton, this was the first evidence of a possible link between Alzheimer’s and failure to convert the D2 dietary form of this vitamin into the usable, storage form.
The UK team’s findings suggest that it may be unwise to use supplemental vitamin D2 as a dementia-deterrent.
Clearly, more research is needed to confirm that hypothesis, but if confirmed, these findings could pave the way for a focus on the most effective way to maintain ample body levels of usable vitamin D.
As Professor Naughton said, “Further investigations are now needed to determine whether simple dietary advice or giving a specific supplement could restore beneficial levels in Alzheimer's patients.” (KU 2012)
How much “D” do we need?
A recent report by the Institute of Medicine recommended maintaining a blood level of 20 to 50 ng/mL.
But many experts in the field say that people need a blood level of 30 to 100 ng/mL to achieve true vitamin D “sufficiency” … a conclusion embodied in the Endocrine Society’s 2011 clinical practice guidelines (Holick MF et al. 2011; Heaney RP et al. 2011).
If a doctor tests your vitamin D levels, make sure that he orders a 25-hydroxyvitamin D test.
In addition, many doctors will call a result of 30 ng/mL (75 nmol/L) “sufficient”, so ask to see your test results.
Vitamin D3 is the “natural” form created when sunrays hit human skin, but it’s abundant only in fatty fishy such as wild salmon (especially sockeye), albacore tuna, herring, mackerel, sablefish, and sardines … see our sidebar, “Fish fit the vitamin D bill”.
The body uses D3 more readily than D2, and D3 is more potent than D2 for producing the “storage” form of vitamin D (25-hydroxyvitamin D), which fulfills the body’s vitamin D functions.
The Endocrine Society currently recommends the following vitamin D intakes, preferable vitamin D3 (Holick MF et al. 2011):
Age 0 to 1 year: 400 to 1,000 IU/day
Age 1 to 18 years: 600 to 1,000 IU/day
All adults over age 18: 1,500 to 2,000 IU/day
Pregnant or nursing women under age 18: 600 to 1,000 IU/day
Pregnant or nursing women over age 18: 1,500 to 2,000 IU/day
There's also general agreement among expert researchers that vitamin D intakes of up to 4000 IU/day are safe. However, when it raised the vitamin D RDAs in 2010, the IOM only raised the upper intake limit to 2,000 IU. Frankly, we rely more on advice from the vitamin D and hormone experts at the Endocrine Society, but you must make your own judgment.
Annweiler C, Beauchet O. Vitamin D-mentia: randomized clinical trials should be the next step. Neuroepidemiology. 2011;37(3-4):249-58. Epub 2011 Dec 7.
Annweiler C, Llewellyn DJ, Beauchet O. Low Serum Vitamin D Concentrations in Alzheimer's Disease: A Systematic Review and Meta-Analysis. J Alzheimers Dis. 2012 Oct 5. [Epub ahead of print]
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]
Annweiler C, Schott AM, Allali G, Bridenbaugh SA, Kressig RW, Allain P, Herrmann FR, Beauchet O. Association of vitamin D deficiency with cognitive impairment in older women: cross-sectional study. Neurology. 2010 Jan 5;74(1):27-32. Epub 2009 Sep 30.
Annweiler C, Schott AM, Rolland Y, Blain H, Herrmann FR, Beauchet O. Dietary intake of vitamin D and cognition in older women: a large population-based study. Neurology. 2010 Nov 16;75(20):1810-6.
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Buell JS, Scott TM, Dawson-Hughes B, Dallal GE, Rosenberg IH, Folstein MF, Tucker KL. Vitamin D is associated with cognitive function in elders receiving home health services. J Gerontol A Biol Sci Med Sci. 2009 Aug;64(8):888-95. Epub 2009 Apr 17.
Buell JS, Tucker KL. The value of physiologic vitamin D as a biomarker of dementia. Drugs Today (Barc). 2011 Mar;47(3):223-31. Review.
Constans T, Mondon K, Annweiler C, Hommet C. [Vitamin D and cognition in the elderly]. Psychol Neuropsychiatr Vieil. 2010 Dec;8(4):255-62. Review. French.
Dickens AP, Lang IA, Langa KM, Kos K, Llewellyn DJ. Vitamin D, cognitive dysfunction and dementia in older adults. CNS Drugs. 2011 Aug;25(8):629-39. doi: 10.2165/11593080-000000000-00000.
Gezen-Ak D, Dursun E, Bilgiç B, Hanagasi H, Ertan T, Gürvit H, Emre M, Eker E, Ulutin T, Uysal O, Yilmazer S. Vitamin d receptor gene haplotype is associated with late-onset Alzheimer's disease. Tohoku J Exp Med. 2012;228(3):189-96.
Heaney RP, Holick MF. Why the IOM recommendations for vitamin D are deficient. J Bone Miner Res. 2011 Mar;26(3):455-7. doi: 10.1002/jbmr.328.
Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, Murad MH, Weaver CM; Endocrine Society. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011 Jul;96(7):1911-30. Epub 2011 Jun 6. Erratum in: J Clin Endocrinol Metab. 2011 Dec;96(12):3908.
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Shah I, Petroczi A, Tabet N, Klugman A, Isaac M, Naughton DP. Low 25OH vitamin D2 levels found in untreated Alzheimer's patients, compared to acetylcholinesterase-inhibitor treated and controls. Curr Alzheimer Res. 2012 Aug 8. [Epub ahead of print]
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.
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