Is vitamin D deficiency associated with Parkinson's disease?

The regulating role of vitamin D in the immune and nervous systems

In a prevalence study, the majority of Parkinson's patients showed decreased vitamin D serum concentrations. These results underline the importance of regular blood level monitoring, especially in older patients.

Among other things, vitamin D is involved in the regulation of processes that are disturbed in multiple sclerosis, Parkinson's disease, and other neurodegenerative diseases. Therefore, a group of scientists from Emory University in the United States was working on whether neurodegenerative diseases are associated with vitamin D deficiency. For this purpose, the vitamin D serum levels of randomly selected Parkinson's patients (n = 100) were compared with those of Alzheimer's patients (n = 97) and neurologically healthy controls (n = 99).

Vitamin D deficiency seems to hit Parkinson's patients particularly hard

25-OH vitamin D levels between 30-70 µg/l are considered healthy. A definite deficiency exists at serum concentrations below 20 ng/ml. In the study, this applied to 23% of Parkinson's patients, only 10% of controls (p = 0.01) and 16% of Alzheimer's patients. In the intermediate range of 20-30 ng/ml, one speaks of a vitamin D insufficiency that occurred in significantly more patients with Parkinson's disease (55%) than in controls (36%, p = 0.008) or Alzheimer's patients (41%, p = 0.05).

Which one is the chicken and which one the egg?

The authors of the study found it somewhat astonishing that the Alzheimer cohort performed so much better than the Parkinson cohort. The question of causality remains open for the time being. A vitamin D deficiency could, on the one hand, be an effect of Parkinson's due to limited mobility and thus low sun exposure. It is also fitting that Parkinson's patients with long periods of illness and particularly severe impairment (Hoehn & Yahr, Stages III-V) showed the lowest vitamin D levels.

On the other hand, hypovitaminosis could contribute to the development of Parkinson's disease

First author Evatt explains: "Previous studies have shown that the area of the brain most severely affected by Parkinson's disease - the substantia nigra - has a particularly high density of vitamin D receptors, which suggests that vitamin D is important for the proper function of these cells. Vitamin D could have a protective effect on the population of neurons that gradually sink in Parkinson's disease."

Animal experiments have also provided evidence that vitamin D protects dopaminergic neurons from toxins. In addition to vitamin D levels, genetic factors and pesticide exposure increase the risk of Parkinson's disease.

Further studies necessary

What is special about the study is that the patients were recruited in an outpatient setting and the cohorts were matched with regard to decisive characteristics (sex, age, APOE genotype, light skin type, the residence of subjects with similar latitude). This is important because deficiency increases with age and previous studies have shown that hospitalized patients have lower vitamin D levels.

Limitations of the study lie in the retrospective study design without longitudinal data, in addition, there were, unfortunately, no surveys on vitamin D intake and sun exposure and more blood samples were taken in summer than in winter.

Outlook

Vitamin D not only supports calcium uptake and bone formation, but there is also increasing evidence of its regulatory role for the immune and nervous systems. Vitamin D deficiency is associated with an increased risk of various malignancies, autoimmune and cardiovascular diseases. Especially in elderly patients, this frequent deficiency should be considered, as a strong correlation between vitamin D deficiency and increased incidence of osteoporosis, falls and hip fractures have been described.

Later work by the authors confirmed the connection between vitamin D deficiency and Parkinson's disease. In addition, an inverse correlation between 25(OH)D2 serum concentrations and Parkinson's could be detected (Wang et al. 2015). Since the 25(OH)D2 levels are independent of sun exposure, these results suggest that the reduced levels of vitamin D are not primarily due to disease-related immobility. A pilot study (phase 4) with vitamin D supplementation in Parkinson's disease was also conducted at Emory University, results have not yet been published.

Sources:
1. Evatt ML et al. Prevalence of Vitamin D Insufficiency in Patients With Parkinson Disease and Alzheimer Disease. Arch Neurol. 2008 Oct;65(10):1348-52.
doi: 10,1001/archneur.65,10,1348.
2. Low Vitamin D Levels Are Risk for Parkinson's Disease, New Evidence Shows | Woodruff Health Sciences Center | Emory University. Available at: http://shared.web.emory.edu/whsc/news/releases/2010/07/low-vitamin-d-levels-are-risk-for-parkinsons-disease.html.

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