The sunshine and MS puzzle

Sunshine and MS are definitely linked but, says Ian Cook, that’s the only thing we can know for certain

With the days getting longer and the sun a little higher in the sky I have found myself reflecting more and more on the complicated and unresolved puzzle of sunshine and multiple sclerosis (MS).

Since my diagnosis, 30 years ago in 1993, I have seen many theories about the causes of MS come and go. The lack of sunshine/vitamin D theory is one of them. In fact, the theory never goes away or gets disproved or proved. One might say the sun never sets on this theory.

In 2003, ten years after I was diagnosed, I heard a Canadian neurologist, Prof. George Ebers, talk at a conference about a “latitude gradient” in MS. Basically, he was saying that the further away from the equator you go and the less sunshine you get, the more cases of MS you find. This is accepted as being as true today as it was in 2003, although no one really knows the reason why.

Vitamin D and MS

It was clear to Ebers that something in sunlight either stopped MS developing or perhaps eased its symptoms. The question was, what was this thing? There were two possibilities. The first was vitamin D which is produced when the sun hits your skin. The other was sunlight itself, or to be more exact ultraviolet (UV) light, perhaps strong sunlight in the UVB band. It was argued this might be doing something to your body in addition to darkening or tanning your skin.

For the past 20 years there has been an ongoing debate about which of these is responsible for the latitude gradient in MS. Those who support lack of vitamin D as a cause of MS point to research including that carried out in Northern Manitoba, Canada. This showed that native Americans living close to polar regions who had little exposure to strong sunshine but ate a lot of oily fish full of vitamin D had far less incidences of MS than you would expect for those living at this latitude. So, did vitamin D, in their fish-rich diet, account for their low levels of MS? And does this mean a lack of vitamin D causes MS?

The debate is still going on and you can find academic papers which support and deny the link between vitamin D and MS. You’ll have probably read the news story earlier in the magazine which found high-dose vitamin D doesn’t have an effect on MS symptoms. Interestingly, the 2022 NICE guidelines on MS say the following: “Do not offer vitamin D solely for the purpose of treating MS”. This suggests that vitamin D or its lack isn’t generally regarded as the answer to the question of what causes MS or how you can treat it.

Sunlight and MS

In view of this, attention naturally turns to sunlight itself. Sunlight also has other effects on the body as well as helping create vitamin D. One research study published in the journal Nutrients in 2018 concluded that the protective effect of sun exposure in MS is most likely brought about through “immunomodulatory mechanisms independent of vitamin D”.

What are these immunomodulatory mechanisms? This too remains the subject of much debate. It is possible that when the sun hits the retina in the back of the eye it influences how much melatonin your body produces, which affects circadian rhythms. This could affect immune regulation.

Cholesterol and MS

Another possibility is that UVB radiation in sunlight hitting the skin may lower levels of bad (LDL) cholesterol which is generally higher in the blood of MSers and may be involved in the disease process itself. One study looking into cholesterol and MS is the current MS-STAT 2 trial, where MSers take high doses of a cholesterol lowering statin (simvastatin) which is believed, may be anti-inflammatory and protect nerves from damage.

It is thought that higher levels of bad (LDL) cholesterol are linked to more severe MS and research into statins in an earlier study (MS-STAT1) found that the rate of brain atrophy (loss of neurons or “brain shrinkage”) was reduced in patients taking simvastatin compared to those taking a placebo. Researchers in the MS-STAT 2 trial are also looking at simvastatin’s effect on brain cell abnormalities as well as changes in blood flow in the brain.

So, is it the case that simvastatin lowers levels of bad (LDL) cholesterol and that levels of LDL cholesterol have also been shown to be reduced when you sit out in the sun? In other words, is sunshine more important because it leads to lower levels of bad cholesterol which lessens disease activity and that, although Vitamin D is produced as well, it doesn’t really have much of an effect on your MS, hence the NICE guidelines?

Vitamin D in pregnancy

One final possibility is that it’s not your exposure to sunlight but your mother’s exposure to sunlight in pregnancy that counts. Those supporting this theory point to a study carried out in 2016 also by George Ebers involving more than 21,000 people with MS which found that people diagnosed with MS in northern latitudes are more likely to have been born in May, and less likely than average to have been born in November. What this study suggests is that low sunlight exposure during winter pregnancies, leads to low maternal vitamin D levels which in some way increase the risk of you developing MS later in your life.

The role of sunlight in MS is certainly far more complex than originally thought. Sadly, like everything with MS, the answer to the question of what causes it or contributes to its cause remains as elusive as it was when George Ebers looked at it all those years ago. Time, sadly, doesn’t appear to answer questions where MS is concerned, only generate new ones.