Vitamin D deficiency linked to Alzheimer's disease

If you are chronically deficient of vitamin D or carry certain genetic variants in the vitamin D receptor, you may be at higher risk of Alzheimer's disease, according to recent studies.

One study showed that people with 25-hydroxyvitamin D or 25(OH)D insufficiency were 2.3 times more likely to have all-cause dementia, 2.5 times more likely to have Alzheimer's disease and 2.0 times more likely to have stroke, compared with those who had sufficient levels.

For the study published in the July 2010 issue of Neurology, Buell J. S. and colleagues from Tufts University surveyed 231 women and 109 men aged 65 to 99 years who received home care for their 25-hydroxyvitamin D and their mental status - whether or not they suffered dementia. They also used MRI to evaluate cerebrovascular disease.

In the study, vitamin D insufficiency was defined as having less than or equal to 20 ng per mL of 25(OH)D and vitamin D deficiency as having less than 10 ng per mL.

Those with dementia had an average level of vitamin D at 16.8 ng per mL, the study found.

Additionally. vitamin D deficiency was found associated with increased white matter hyper-intensity volume and prevalence of large vessel infarcts.

Buell's study is not the only one linking vitamin D insufficiency to elevated risk of Alzheimer's disease.

Pogge E of Midwestern University College of Pharmacy-Glendale in Glendale, Arizona conducted a thorough review of studies published prior to Jan 2010 and found that vitamin D deficiency was not only linked to dementia, particularly  Alzheimer's disease, but also low cognitive test scores in Alzheimer's patients.

Pogge published his review in the July 2010 issue of The Consultant pharmacist.

Vitamin D and Cognition in AD Patients

One study published in 2008 in the Dementia and Geriatric Cognitive Disorders revealed a relationship between vitamin D status and cognition in patients with probable Alzheimer's disease.

Oudshoorn C and colleagues from Erasmus University Medical Center in Rotterdam, The Netherlands found higher serum vitamin D3 levels were associated with better cognitive test performance in patients with Alzheimer's.

The researchers tested vitamin D and b1, b6 and b12 in 225 outpatients who were diagnosed with probable Alzheimer's disease and found that those who had sufficient vitamin D, specifically 25-hydroxyvitamin D(3) had significantly higher Mini-Mental State Examination test scores than those who had insufficiency of vitamin d.

Other B vitamins were not associated.

Vitamin D Related Genetics and AD

Certain genetic variants results in low affinity of vitamin D to its receptor which virtually reduces the concentration of vitamin D. 

Gezen-Ak D. and colleagues from Istanbul University in Turkey examined the association between the single nucleotide polymorphisms (SNP) in the vitamin D receptor (VDR) gene and neurodegenerative diseases and neuronal damage.

In the study, the researchers genotyped ApaI and TagT in intron 8 and exon 9 of the ligand-binding site of VDR gene in 104 patients with Alzheimer's disease and 109 age matched controls.

They found Aa type was more often present in patients with Alzheimer's disease while AT was more commonly seen in the healthy controls, suggesting that vitamin d plays a role in the degenerative disease.

The findings were reported in 2007 in Tohoku Journal of Experimental Medicine.

This week, one study presented at the Alzheimer’s Association International Conference in Honolulu, Hawaii suggests that Vitamin D deficiency can cause Alzheimer's.

The study of 3325 people aged 65 conducted by researchers at the University of Exeter Peninsula Medical School showed that cognitive impairment was 40 percent more likely found in people who were vitamin D deficient.

Exposure of the face and hands to sun at the  hottest hours for 15 to 20 minutes can result in 10,000 IUs of vitamin D. Those who are old or have dark skin are more likely to have vitamin D deficiency.

By David Liu