Comparison of Serum Free and Bioavailable 25-Hydroxyvitamin D Levels in Alzheimer’s Disease and Healthy Control Patients

Abstract

Objective Many studies have investigated lower 25-hydroxyvitamin D (25[OH]D) levels in patients with Alzheimer’s disease (AD) compared with those in control patients. In the present study, we aimed to evaluate serum free and bioavailable 25(OH)D levels in patients with AD and in healthy control patients. Methods The AD group consisted of 85 patients aged >60 years who were diagnosed with possible AD according to National Institute on Aging-Alzheimer’s Association criteria and 85 healthy control patients. Serum levels of total 1,25-dihydroxyvitamin D, total 25(OH)D, vitamin D binding protein (VDBP), parathormone, calcium, phosphorus and albumin, free 25(OH)D, bioavailable 25(OH)D, and the bioavailable 25(OH)D/total 25(OH)D ratio were compared in both groups. Results Total 25(OH)D, free 25(OH)D, bioavailable 25(OH)D, and the bioavailable 25(OH)D/total 25(OH)D ratio were significantly lower (P <.001, P <.001, P <.001, P <.05, respectively) in the AD group, whereas the VDBP level was significantly higher (P <.05) in the AD than in the control group. Conclusion Free and bioavailable 25(OH)D detected at lower levels in patients with AD limit the target central effects of 25(OH)D; this result suggests that reduced levels of the active free form of vitamin D may be a risk factor for AD and dementia.

Serum Vitamin D as a Biomarker in Autoimmune, Psychiatric and Neurodegenerative Diseases

“…It should be noted that the authors carried out 25(OH)D measurements using RMPs and SRMs, which strengthens to the results. Similar findings have also been described by many studies [ 99 , 100 , 101 , 102 , 103 ]. In 2017, Licher et al found that Vitamin D serum 25(OH)D concentrations below 25 nmol/L were associated with a higher incidence of AD [ 99 ].…”

Brain vitamin D forms, cognitive decline, and neuropathology in community‐dwelling older adults

“…21 The latter study used the less-precise approach of calculating free 25(OH)D 47 to compare concentrations between adults ≥60 years of age diagnosed with AD and those with normal cognitive function. 21 It is now known that megalin, which is integral for cellular uptake of bound vitamin D, is expressed in neuronal tissues and has been implicated in neurodegenerative processes, 48,49 so the importance of free 25(OH)D specifically to brain health remains to be clarified. This study's findings should be interpreted in the context of its strengths and limitations.…”

COVID-19 and neurological sequelae: Vitamin D as a possible neuroprotective and/or neuroreparative agent

“…Vitamin D deficiency has been linked to several neurological illnesses such as Parkinson's disease, schizophrenia, depression, and cognitive decline, suggesting that it plays a vital role in maintaining normal CNS function [93] , [94] , [95] . Another study in an animal model of oxidative stress and neurodegeneration reported that vitamin D plays an important role in memory and cognition, and that its deficiency could accelerate cognitive impairment [96] : both the immunomodulatory and antioxidant effects of vitamin D significantly reduced different pro-inflammatory interleukins and increased the synthesis of anti-inflammatory chemical mediators ( Fig.…”