Daily sun exposure of 1 to 2 hours is associated with a 7.4-fold reduced risk of paediatric multiple sclerosis (MS) compared to 30 minutes or less.
Spring is coming and we are looking forward to more sun and longer days. Two pertinent studies recently presented at the ACTRIMS (Americas Committee for Treatment and Research in Multiple Sclerosis) Virtual Congress, 25-27 Feb 2021, are summarised here.
Low sunlight, exposure to ultraviolet light and vitamin D are known modifiable risk factors for adult MS. About 5% of MS sufferers are under 18 years of age. For this population, the evidence is much thinner.
The first study on the association between sun exposure and the development of paediatric MS examined 332 MS patients aged 4-22 years from 16 MS centres in different regions of the USA. The control group consisted of 534 age- and sex-matched participants without MS. After adjusting for factors such as age, sex, season at birth, skin colour, maternal education level, smoking, obesity and EBV infection, children who had more frequent sun exposure had a significantly lower risk of developing paediatric MS.
"To reduce MS incidence, parents should be encouraged to let their children spend at least 30 minutes a day outside in the sun" ...lead author Prince Sebastian, from the Australian National University, Canberra, states. "This is particularly important for children with a positive family history of MS."
The use of sunscreen did not appear to affect the risk. "You can use adequate sunscreen and still get in the benefits of sun exposure in terms of MS risk." The researchers had expected that greater use of sunscreen would limit effective sun exposure and thus increase MS risk. But such an effect was not evident, probably because people who use sunscreen get more sun anyway.
In the 'EnvIMS' study from 20181 for example (n = 6,279), the lowest sun exposure was associated with an almost 50% increased risk compared to those with the highest sun exposure. In contrast to the current study, however, an effect of sun protection was evident here.
A limitation of the current study is that only self-reported time in the sun over the past summer was recorded and data on vitamin D supplementation, for example, were missing.2 Nevertheless, both studies contribute to a growing body of evidence suggesting that sun exposure is beneficial for MS.
On this topic, new data for adult MS patients were also presented at the congress. From previous studies, a significance of vitamin D deficiency for the development of MS, but also for disease activity and progression, is known. Cognitive impairment, and in particular slowed information processing, is also a common complication of MS. There is also evidence for the role of hypovitaminosis.
In a recently presented study from Italy (n = 80), lowered vitamin D levels (< 30 ng/ml) correlated significantly with worsened cognition and scores on the SDMT (Symbol Digit Modalities Test).
This fits with the results of the 'BENEFIT' study published last year, which followed 278 MS patients for longer. Here, a 20 ng/ml higher mean vitamin D level in the first 2 years of the study was associated with a 65% lower likelihood of poor performance on the PASAT (Paced Auditory Serial Addition Test) after 11 years.
First author of the Italian paper, Dr. Eleonora Virgilio, from the MS Centre at Eastern Piedmont University, says: "The possible effects of vitamin D on both cognition and early disability in newly diagnosed MS patients should be further investigated, as this association could represent a marker for future disability, which would argue for the need for immediate supplementation."3 Over a follow-up period of two years, the researchers also reported a significant correlation between serum vitamin D levels at diagnosis and early disability (measured by the MSSS).
References:
1. Magalhaes, S. et al. Shedding light on the link between early life sun exposure and risk of multiple sclerosis: results from the EnvIMS Study. International Journal of Epidemiology 48, 1073-1082 (2019).
2. Vitamin D Deficiency Linked to Early Cognitive Impairment in MS. ACTRIMS Forum 2021: Poster #P158. Presented February 25, 2021. medscape.
3. Sun Exposure Linked to Reduced Pediatric MS Risk. Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) 2021: Abstract S1.3. Presented February 25, 2021. Medscape.