Alzheimer's disease is a brain disorder correlated with major reduction of neurons to the respective target areas through destruction of brain cells, causing cognitive modalities severe enough to affect language communication, memory, lifelong hobbies or social life. Alzheimer's gets worse over time, and it is fatal.
According to statistic, over 25 million people in the world today are affected by dementia and most are suffering from Alzheimer's disease.
Vitamin D is a fat-soluble secosteroids found in small amount in few foods, including salmon, mackerel, sardines and tuna. The vitamin plays an important role in modulation of cellular proliferation, apoptosis induction, tumor growth suppression and promotion in absorption of minerals, including calcium, iron, magnesium, phosphate and zinc.
1. Vitamin D receptors(VDR)
Vitamin D receptors, also known as NR1I1 (nuclear receptor subfamily 1, group I, member 1), with functions of regulation in many metabolic pathways, including cancers, play an important role in risk of Alzheimers' disease. Polymorphisms in the vitamin D receptor (VDR), and insufficient serum 25 hydroxyvitamin D3 levels patients have been found to associate with age- dependent cognitive decline(1). The study of Vitamin D(3), a neurosteroid that mediates its effects via the vitamin D receptor (VDR) also indicated a possible link between AD and certain VDR polymorphisms in early onset of AD(2) through suppression of VDR by Aβ(3). Treatment of Vitamin D was found effectively in inhibition of Aβ induced alterations in primary cortical neurons(4). The Istanbul University in study of the association of between VDR gene and late-onset Alzheimer's disease (AD) with 104 cases of dementia of Alzheimer type and 109 age-matched controls, showed an significant increased Aa genotype in AD patients than health individuals with the same genotype, of that may be an indication of "Aa" genotype associated to increased risk of developing AD. In the comparison of "AA" genotype, risk of AD in men with Aa genotyes are 2.3 times higher(5).
2, Plasma of vitamin D
Suggestion of serum levels of vitamin D used as diagnosis for indication of early onset of Alzheimer's' diseases may be controversial. Some researchers suggested that lower plasma nutrient levels only a indication for impaired systemic availability of several nutrients in AD(6). The Kingston University study showed level of 25hydroxyvitamin D (25OHD) was found to be lower in patients with the disease, arising from extremely low levels of 25OHD2 along with low levels of 25OHD3.(7). In the study of the correlation of Alzheimer's disease and osteoporosis, the Heinrich-Heine-University showed that 25 (OH) vitamin D plasma levels were low normal and of equal amount in all groups except for the osteoporosis group(8).
Epidemiological studies, focusing vitamin D and its derivative in reduced risk of Alzheimer's diseases have not been consistent. Researchers indicated that Gene polymorphisms alternation of vitamin D metabolism are also associated with a higher incidence or a worse disease prognosis, and despite the links between vitamin D deficiency and the risks of developing neurological disorders, there is, to date, no proof that supplementation could alter the course of these diseases(9). Study of the effects of vitamin D showed an indication of prevention of neurons cytotoxicity and apoptosis through downregulating LVSCC A1C(L-type voltage-sensitive calcium channel with function of gene expression, synaptic efficacy, and cell survival) and upregulating VDR and balancing nerve growth factor (NGF) expressions(10). Researchers at the 1Vietnamese American Medical Research Foundation, suggested that vitamin D supplements appeared beneficial to patients of AD through many mechanisms including regulating micro-RNA, enhancing toll-like receptors, modulating vascular endothelial factor expression, angiogenin, and advanced glycation end products, etc.(11). The combination of memantine with vitamin D, a neurosteroid hormone, in the joint study, showed an evidence lesser cortical axons degeneration after exposure to amyloid-beta peptide or glutamate in microfluidic neuronal cultures.(12). Unfortunately, regardless to the effectiveness of vitamin D in reduced risk of cognitive impairment or Aβ, many researchers still believed that there is no truly effective therapy has been developed for Alzheimer's disease or mild cognitive impairment(13).
Taking altogether, without going into reviews, vitamin D may be considered as a therapeutic treatment in reduced risk of Alzheimers' diseases, through many mechanisms, including induction of Aβ, regulation of micro-RNA expression, etc.. Over doses of vitamin D supplement may cause excessive calcium absorption, calcification, Urinary stones etc. please make sure to follow the guideline of the Institute of Medicine of the National Academies.
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(1) A novel perspective for Alzheimer's disease: vitamin D receptor suppression by amyloid-β and preventing the amyloid-β induced alterations by vitamin D in cortical neurons by Dursun E1, Gezen-Ak D, Yilmazer S.(PubMed)
(2) Vitamin D receptor gene haplotype is associated with late-onset Alzheimer's disease.
(3) A new mechanism for amyloid-β induction of iNOS: vitamin D-VDR pathway disruption by Dursun E1, Gezen-Ak D, Yilmazer S(PubMed)
(4) A novel perspective for Alzheimer's disease: vitamin D receptor suppression by amyloid-β and preventing the amyloid-β induced alterations by vitamin D in cortical neurons by Dursun E1, Gezen-Ak D, Yilmazer S(PubMed)
(6) Plasma nutrient status of patients with Alzheimer's disease: Systematic review and meta-analysis by Lopes da Silva S1, Vellas B, Elemans S, Luchsinger J, Kamphuis P, Yaffe K, Sijben J, Groenendijk M, Stijnen T.(PubMed)
(7) Low 25OH vitamin D2 levels found in untreated Alzheimer's patients, compared to acetylcholinesterase-inhibitor treated and controls by Shah I1, Petroczi A, Tabet N, Klugman A, Isaac M, Naughton DP.(PubMed)
(8) Blood biomarkers of osteoporosis in mild cognitive impairment and Alzheimer's disease by Luckhaus C1, Mahabadi B, Grass-Kapanke B, Jänner M, Willenberg H, Jäger M, Supprian T, Fehsel K.(PubMed)
(9) [Vitamin D and neurology].[Article in French] by Thouvenot É1, Camu W(PubMed)
(11) The role of vitamin D in Alzheimer's disease: possible genetic and cell signaling mechanisms by Lu'o'ng KV1, Nguyen LT.(PubMed)
(12) Combination of memantine and vitamin D prevents axon degeneration induced by amyloid-beta and glutamate by Annweiler C1, Brugg B, Peyrin JM, Bartha R, Beauchet O(PubMed)