Previous research has shown that low exposure to ultraviolet (UV) light from the sun and low levels of vitamin D is linked to an increased risk of developing MS. However, relatively little research has looked at whether sun exposure over a person’s lifetime or vitamin D affects the severity or course of MS.
New Australian research has answered this question using information gathered as part of the Ausimmune Study, a multi-centre study that has investigated the environmental factors associated with a first attack of MS-like symptoms (known as a first demyelinating event) and has then followed these participants for many years. This long term tracking of the participants makes the Ausimmune study uniquely powerful compared to other research designs which only compare people with MS to people without MS at a single snapshot in time.
Led by Professor Bruce Taylor from the Menzies Institute for Medical Research in Hobart, this study followed 145 people who had experienced a first demyelinating event for five years. Researchers determined the participants’ lifetime sun exposure using questionnaires asking about sun behaviour and time spent outside at different ages. They estimated their exposure to UV light via ambient UV light measurements taken from their location of home and work for each month of each participant’s life. Measurements of vitamin D levels in the blood were also made at the start of the study, at the halfway point and after five years.
Published in Frontiers in Neurology, the study found that higher lifetime sun exposure lowered the chance that an individual would convert to a diagnosis of MS following a first demyelinating event. For a diagnosis of MS to be made, two separate demyelinating events need to have taken place, so higher sun exposure protected people from experiencing the second demyelinating event over the following five years.
Higher UV exposure prior to experiencing a first demyelinating event, particularly during childhood and adolescence, also reduced the risk of relapse over the five years.
When they looked at the UV exposure of the whole group following the first demyelinating event, it was not linked to a reduced risk of converting to MS or experiencing a relapse. However, most participants had relatively stable sun exposure over the course of the study.
There were a smaller group of people who did significantly increase their sun exposure over the five years following their first demyelinating event, and these people did have a reduced risk of converting to MS and reduced their chance of having a relapse. The opposite was also true – those who significantly reduced their sun exposure increased their chance of conversion to MS and of having a relapse. This finding implies that sun exposure can have a beneficial effect on the course of the disease in some people.
The level of vitamin D in a person’s blood was not linked to whether they converted to a diagnosis of MS or had a relapse over the study period. Similarly, people who had vitamin D levels which changed significantly over the study did not have any corresponding change to their risk of relapses or conversion to MS. While other research has found that vitamin D does play a role in the course of a person’s MS, this study implied it is sun exposure that has the dominant effect, rather than vitamin D. This study provides evidence that interventions for MS that safely increase exposure to UV, such as narrow band UV radiation therapy, may be more beneficial for MS than vitamin D alone.
Another study, from Kaiser Permanente in Southern California, looked into whether lifetime sun exposure and vitamin D altered risk in different racial groups. The study, published in the journal Nutrients aimed to isolate the effects of sun exposure and vitamin D on MS risk by taking into account differences such as genetic ancestry.
Called the MS Sunshine Study, the research looked at people with MS from white, black and Hispanic backgrounds and compared them to people without MS. They found that higher lifetime sun exposure lowered the risk of developing MS in people with either a black or white background, with a similar trend seen in the Hispanic group. This effect was independent of the level of vitamin D in their blood. Higher levels of vitamin D in the blood was associated with a lower risk of MS only in people from a white background. However, MS risk was not reduced by having higher levels of vitamin D in people of black or Hispanic descent.
This research study further supports the idea that sunshine is having an independent effect on MS risk. Taken together, the two studies show that sunshine is capable of having an effect on the immune system beyond that of its ability to produce vitamin D in the skin.
A third study, from researchers based in Canada and the US published in the journal Neurology, has also shown that sun exposure in early life can change the risk of developing MS. The study compared the lifetime and sun exposure in different seasons of people with MS to people without MS. They also attempted to separate out the effects of sun exposure by taking into account other factors including genetic ancestry, smoking and vitamin D supplementation. Most of the people taking part in this study were of a white background.
They found that living in an area with higher sun exposure prior to the onset of disease, in particular the 5 to 15 years before onset, lowered the risk of developing MS. They also found childhood sun exposure was important, in that between the ages of 5 to 15 years, living in an area with higher sun exposure and having high sun exposure during summer was associated with a lower MS risk later in life. Unlike the two previous studies, this third study did not directly measure the vitamin D levels in the participants, however, this study adds further weight to the role of sun exposure in the risk of developing MS.