Sun Exposure, Vitamin D, and MRI Measures in MS
Sun Exposure, Vitamin D, and MRI Measures in MS
Purpose To assess the relationships of sun exposure history, supplementation and environmental factors to vitamin D levels in multiple sclerosis (MS) patients and to evaluate the associations between sun exposure and MRI measures.
Methods This study included 264 MS patients (mean age 46.9±10 years, disease duration 14.6±10 years; 67.8% relapsing–remitting, 28% secondary progressive and 4.2% primary progressive MS) and 69 healthy controls. Subjects underwent neurological and 3 T MRI examinations, provided blood samples and answered questions to a structured questionnaire. Information on race, skin and eye colour, supplement use, body mass index (BMI) and sun exposure was obtained by questionnaire. The vitamin D metabolites (25-hydroxy vitamin D3, 1, 25-dihydroxy vitamin D3 and 24, 25-dihydroxy vitamin D3) were measured using mass spectrometry.
Results Multivitamin supplementation (partial correlation rp=0.29, p<0.001), BMI (rp=−0.24, p=0.001), summer sun exposure (rp=0.22, p=0.002) and darker eye colour (rp=−0.18, p=0.015) had the strongest associations with vitamin D metabolite levels in the MS group. Increased summer sun exposure was associated with increased grey matter volume (GMV, rp=0.16, p=0.019) and whole brain volume (WBV, rp=0.20, p=0.004) after correcting for Extended Disability Status Scale in the MS group. Inclusion of 25-hydroxy vitamin D3 levels did not substantially affect the positive associations of sun exposure with WBV (rp=0.18, p=0.003) and GMV (rp=0.14, p=0.026) in the MS group.
Conclusions Sun exposure may have direct effects on MRI measures of neurodegeneration in MS, independently of vitamin D.
Multiple sclerosis (MS) is a degenerative, chronic inflammatory disease of the CNS that causes demyelination, lesion formation and CNS atrophy. The CNS damage in MS results from abnormal immune responses but there is also neurodegeneration and progressive neuronal loss.
Latitude is a prominent environmental factor associated with the risk of developing MS, which increases with increasing distance from the equator in both the northern and southern hemispheres. Latitude is an important determinant of sun exposure, and areas at higher latitudes receive less potent ultraviolet radiation (UVR) exposure. Climate and seasonal variation also affect UVR exposure. Outdoor temperature and sunny weather are also important determinants of human activities and behaviours that could result in sun exposure. Sun exposure is also being minimised as a consequence of public health education campaigns, which are promoting the use of sun blocking agents in order to reduce the incidence of skin cancer.
UVR exerts an immunosuppressive effect on the immune system through multiple mechanisms and has been associated with the risk of autoimmune disease such as MS, type 1 diabetes and rheumatoid arthritis. UVR causes local immunosuppression, resulting in less hypersensitivity reactions. Secondly, it helps limit melatonin secretion, which can modulate T cell proliferation and activity. More importantly, UVR increases vitamin D production, and vitamin D has been shown to have pleiotropic immunomodulatory activities. There are challenges in assessing the relationship of sunlight exposure to clinical outcomes in MS because disability progression can affect sun exposure. Furthermore, sunlight exposure can affect vitamin D levels, making it difficult to assess which of the two exposures is relevant for modulating pathophysiological mechanisms of brain injury.
Vitamin D levels are dependent on sun exposure because ultraviolet light is required for the first step in the synthesis of vitamin D from 7-dehydrocholesterol in the skin. Several studies have examined the associations of vitamin D with clinical and MRI measures in MS patients. These studies have reported associations with relapse rates. Adverse disability and disability changes on the Extended Disability Status Scale (EDSS) and the MS Severity Scale are associated with low vitamin D levels. The associations of vitamin D levels with MRI measures in MS patients have been examined but the associations appear more modest.
The goal of this study was to assess the interdependencies of sunlight and vitamin D supplementation to vitamin D metabolite levels in MS patients and to evaluate the associations between sun exposure to MRI measures of brain injury in MS.
Abstract and Introduction
Abstract
Purpose To assess the relationships of sun exposure history, supplementation and environmental factors to vitamin D levels in multiple sclerosis (MS) patients and to evaluate the associations between sun exposure and MRI measures.
Methods This study included 264 MS patients (mean age 46.9±10 years, disease duration 14.6±10 years; 67.8% relapsing–remitting, 28% secondary progressive and 4.2% primary progressive MS) and 69 healthy controls. Subjects underwent neurological and 3 T MRI examinations, provided blood samples and answered questions to a structured questionnaire. Information on race, skin and eye colour, supplement use, body mass index (BMI) and sun exposure was obtained by questionnaire. The vitamin D metabolites (25-hydroxy vitamin D3, 1, 25-dihydroxy vitamin D3 and 24, 25-dihydroxy vitamin D3) were measured using mass spectrometry.
Results Multivitamin supplementation (partial correlation rp=0.29, p<0.001), BMI (rp=−0.24, p=0.001), summer sun exposure (rp=0.22, p=0.002) and darker eye colour (rp=−0.18, p=0.015) had the strongest associations with vitamin D metabolite levels in the MS group. Increased summer sun exposure was associated with increased grey matter volume (GMV, rp=0.16, p=0.019) and whole brain volume (WBV, rp=0.20, p=0.004) after correcting for Extended Disability Status Scale in the MS group. Inclusion of 25-hydroxy vitamin D3 levels did not substantially affect the positive associations of sun exposure with WBV (rp=0.18, p=0.003) and GMV (rp=0.14, p=0.026) in the MS group.
Conclusions Sun exposure may have direct effects on MRI measures of neurodegeneration in MS, independently of vitamin D.
Introduction
Multiple sclerosis (MS) is a degenerative, chronic inflammatory disease of the CNS that causes demyelination, lesion formation and CNS atrophy. The CNS damage in MS results from abnormal immune responses but there is also neurodegeneration and progressive neuronal loss.
Latitude is a prominent environmental factor associated with the risk of developing MS, which increases with increasing distance from the equator in both the northern and southern hemispheres. Latitude is an important determinant of sun exposure, and areas at higher latitudes receive less potent ultraviolet radiation (UVR) exposure. Climate and seasonal variation also affect UVR exposure. Outdoor temperature and sunny weather are also important determinants of human activities and behaviours that could result in sun exposure. Sun exposure is also being minimised as a consequence of public health education campaigns, which are promoting the use of sun blocking agents in order to reduce the incidence of skin cancer.
UVR exerts an immunosuppressive effect on the immune system through multiple mechanisms and has been associated with the risk of autoimmune disease such as MS, type 1 diabetes and rheumatoid arthritis. UVR causes local immunosuppression, resulting in less hypersensitivity reactions. Secondly, it helps limit melatonin secretion, which can modulate T cell proliferation and activity. More importantly, UVR increases vitamin D production, and vitamin D has been shown to have pleiotropic immunomodulatory activities. There are challenges in assessing the relationship of sunlight exposure to clinical outcomes in MS because disability progression can affect sun exposure. Furthermore, sunlight exposure can affect vitamin D levels, making it difficult to assess which of the two exposures is relevant for modulating pathophysiological mechanisms of brain injury.
Vitamin D levels are dependent on sun exposure because ultraviolet light is required for the first step in the synthesis of vitamin D from 7-dehydrocholesterol in the skin. Several studies have examined the associations of vitamin D with clinical and MRI measures in MS patients. These studies have reported associations with relapse rates. Adverse disability and disability changes on the Extended Disability Status Scale (EDSS) and the MS Severity Scale are associated with low vitamin D levels. The associations of vitamin D levels with MRI measures in MS patients have been examined but the associations appear more modest.
The goal of this study was to assess the interdependencies of sunlight and vitamin D supplementation to vitamin D metabolite levels in MS patients and to evaluate the associations between sun exposure to MRI measures of brain injury in MS.
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