Fear of Alzheimer’s disease ranks among the greatest anxieties among aging people.
That concern is well-founded, since Alzheimer's is the most common form of dementia – afflicting some 13 million people worldwide – and rates seem to be on the rise.
Most cases develop after age 60 – the so-called late-onset form – and heredity plays a major role in the risk for both early- and late-onset Alzheimer’s (see our sidebar, “Genetic factors in Alzheimer’s”).
Diet also seems to play a role, though it appears to exert less influence in people with the riskiest genetic profiles (see our sidebar, “Nutrients and foods for Alzheimer’s?”).
Prior population studies indicated that higher dietary intakes of vitamin D may offer substantial protection ... though possibly a bit more for women than for men (Slinin Y et al. 2010; Slinin Y et al. 2012).
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
*For our full test results, click here.
Two years ago a team from France’s Angers University Hospital published a “cross-sectional” study in 752 women aged 75 or older (Annweiler C et al. 2010).
About 17 percent of the participants had vitamin D deficiency … defined as a blood level below 10 nanograms per milliliter (ng/mL). The women deficient in vitamin D scored the lowest on mental tests and showed the greatest signs of cognitive impairment.
Those results were echoed in two similar studies from Tufts University (Buell JS et al. 2009; Buell JS et al. 2010).
An Italian study found that the risk of cognitive decline was 60 percent higher in elderly adults with severely deficient vitamin D levels – i.e., level below 10 ng/mL – when compared to people with blood levels above 30 ng/mL, which are generally considered “sufficient” if not optimal (Dickens AP et al. 2011).
Likewise, a U.S. study in elderly men found that the odds of cognitive decline were 41 percent higher in those whose vitamin D levels fell below 20 ng/mL, compared to the men with levels above 30 ng/mL (Dickens AP et al. 2011).
Now, the results of another study by the team from Angers University Hospital suggest that diets that supply ample vitamin D from foods may help protect women against late-onset Alzheimer’s.
French study links vitamin D lack to women’s Alzheimer’s risk
The Angers University Hospital group – led by Cedric Annweiler, M.D., Ph.D. – has focused the relationship between vitamin D and Alzheimer’s disease.
As we said, their study published in 2010 linked low vitamin D blood levels to higher risk of this most common form of dementia.
Now, they report that women with higher intakes of vitamin D may be at a lower risk of developing Alzheimer’s disease … but not of developing other, less common forms of dementia (Annweiler C et al. 2012).
In this “prospective” study, they followed 498 women – aged 76 to 84 (average 79.8 years) – for seven years. None were taking vitamin D supplements, and all were living at home.
The women with the highest estimated vitamin D intakes from food were 77 percent less likely to have developed Alzheimer’s within seven years.
Genetic factors in Alzheimer’s
The APOE gene comes in several different forms, or alleles, three of which – APOE2, APOE3, and APOE4 – occur most often.
People who develop Alzheimer's are more likely to have an APOE4 allele than people who do not develop the disease.
APOE4 is present in about 25 to 30 percent of all people, and in about 40 percent of people with late-onset Alzheimer's.
People who inherit one or two APOE4 alleles also tend to develop the disease at an earlier age than those who do not have any APOE4 alleles.
Carriers of two E4 alleles have between 10 and 30 times the risk of developing AD by 75 years of age, compared to those not carrying any E4 alleles.
Why would the APOE variant matter?
Alzheimer’s disease is characterized by – though not necessarily caused by – build-up of beta-amyloid protein plaque and tau protein tangles in the brain.
And some evidence suggests that people with APOE4 alleles are not as efficient at removing amyloid plaque.
These results were calculated after adjusting for relevant factors such as age, body mass index, initial cognitive performance, education level, physical activity, sun exposure, and several other potential “confounding” factors.
Vitamin D intake made no difference to the risk of developing other forms of dementia.
As the French wrote, “To the best of our knowledge, the present study is the first one to use a prospective design, allowing us to conclude that the low consumption of vitamin D precedes the onset of Alzheimer’s disease, although eating lots of vitamin D rich foods is associated with a lower risk of developing Alzheimer’s disease.” (Annweiler C et al. 2012).
And as they noted, the potential brain benefits of fish rich in vitamin D may be linked to the other nutrients in them:
“In particular, there is reasonably good evidence that eating fish reduces the risk of dementia including Alzheimer’s. This effect is generally attributed to the omega-3 polyunsaturated fatty acids ...” (Annweiler C et al. 2012)
Why would vitamin D help deter Alzheimer’s disease?
Alzheimer’s is characterized by a build-up of plaque from beta-amyloid deposits and tau protein “tangles”.
These anomalies are associated with brain cell damage and death from oxidative stress … which in turn is blamed for loss of cognitive function and an increased risk of Alzheimer’s.
The French research team points out that in rodents, vitamin D has been linked to protection of the brain’s hippocampus – a center of memory and mood – and appears to influence the production and clearance of beta-amyloid proteins (Dickens AP et al. 2011).
It seems that reasons to eat fatty fish just keep growing … aside from sheer enjoyment of their flavor.
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.
Buell JS, Dawson-Hughes B, Scott TM, Weiner DE, Dallal GE, Qui WQ, Bergethon P, Rosenberg IH, Folstein MF, Patz S, Bhadelia RA, Tucker KL. 25-Hydroxyvitamin D, dementia, and cerebrovascular pathology in elders receiving home services. Neurology. 2010 Jan 5;74(1):18-26. Epub 2009 Nov 25.
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.
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.
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]
Slinin Y, Paudel ML, Taylor BC, Fink HA, Ishani A, Canales MT, Yaffe K, Barrett-Connor E, Orwoll ES, Shikany JM, Leblanc ES, Cauley JA, Ensrud KE; Osteoporotic Fractures in Men (MrOS) Study Research Group. 25-Hydroxyvitamin D levels and cognitive performance and decline in elderly men. Neurology. 2010 Jan 5;74(1):33-41. Epub 2009 Nov 25.