Although it is generally thought that vitamin D status (indicated by 25(OH)D blood serum levels) is an indicator of recent sun exposure, researchers from the Australian National University have suggested that past and current exposure to UV sunlight may have separate roles to serum vitamin D levels in the prevention of multiple sclerosis (MS) – a chronic disease of the brain and spinal cord.
Writing in the journal Neurology, the researchers warned that if the findings presented in the current study are confirmed, then advocating vitamin D supplementation alone “may be a less effective preventive intervention than has been suggested by previous epidemiologic studies” as both UV sun exposure and vitamin D status may have separate roles, and should therefore both be counted as important in prevention.
“Here both recent sun exposure and current 25(OH)D levels contributed independently to the reduced FDE risk [an early marker of MS development],” said the authors, led by Dr. Robyn Lucas from the National Centre for Epidemiology and Population Health, at The Australian National University.
“Previous studies have found similar results, but this is the first study to look at people who have just had the first symptoms of MS and haven’t even been diagnosed with the disease yet,” said Lucas.
Multiple sclerosis (MS) is a chronic autoimmune disease in which the central nervous system (CNS) is damaged by the body’s immune cells, and reducing the ability of nerve cells in the brain and spinal cord to communicate with each other.
The authors said that full diagnosis of MS is often preceded by a first episode of symptoms lasting just a few days or weeks – referred to as first demyelinating events (FDEs).
Though potentially important implications for preventive interventions for MS, Lucas and colleagues said that previous human studies have not measured past sun exposure before the onset of MS, and thus have been unable to differentiate between what are potentially separate and interlinked causal roles in sun exposure and vitamin D status.
The new research; a large, epidemiologic case controlled study addressed this issue in study design by testing part and current sun exposure, in addition to serum vitamin D status and supplementation details – in order to comprehensively assess the links between vitamin D status, sun exposure and the risks of developing MS.
Lucas and her colleagues reported that higher recent and lifetime sun exposure, and higher serum 25(OH)D levels, were all independently associated with a reduced risk of a first demyelinating events (FDE).
They said that these associations remained after adjustment for potential confounders, and did not vary by study region, gender, or type of FDE event.
Lower past leisure time UV dose (from age six years to current age), taking account of residential location, was found to be a strong predictor of FDE. Whilst a similar effect of decreased FDE risk, was observed for higher 25(OH)D serum levels.
The authors also noted that since the current study on based on a largely male cohort, its findings do not support previous work suggesting that vitamin Ds protective effect is confined to females.
“These findings do raise the possibility that both (recent) vitamin D status and (recent and/or longterm) sun exposure influence FDE onset,” wrote the authors.
As a result they explained that both will need to be further evaluated in independent clinical trials for multiple sclerosis prevention.
Lucas warned that people should their sun exposure due to risks of skin cancer, and explained that exposure to the sun has not been shown to benefit people who already have MS.
She also noted that the risks associated with tanning beds far outweigh any possible protective effect against MS or FDE.
Volume 76, Number 6, Pages 540 – 548, doi: 10.1212/WNL.0b013e31820af93d
“Sun exposure and vitaminDare independent risk factors for CNS demyelination”
Authors: R.M. Lucas, A.L. Ponsonby, K. Dear, P.C. Valery, M.P. Pender, B.V. Taylor, et al