'Vikings could be to blame for why Scots have highest levels of multiple sclerosis' is the somewhat imaginative leap taken by the Daily Mail as it reports on multiple sclerosis (MS) rates in Aberdeen, Orkney and Shetland.
The headline is based on a study that tried to find out if numbers of people with the disease in these areas had changed over the last 30 years. Researchers were specifically looking at the prevalence of MS, which affects muscle movement, balance and vision.
The study found that over the combined area, 248 per 100,000 inhabitants had MS (approximately 0.25%), while in Orkney the figure was over 400 per 100,000 (approximately 0.4%), the highest recorded rate worldwide. Women were more affected than men, with about 1 in 170 women in Orkney (approximately 0.59%) affected. These figures are a marked increase compared with earlier research carried out in the 1980s.
Despite the Mail’s headline, the researchers provide no firm conclusions about what could explain the high rates. They speculate the following two factors may be involved:
- genetics – Orkney is an island community that was settled by the Vikings
- the environment – such as lower levels of vitamin D exposure
Vitamin D production is stimulated by sunlight, so the further away from the equator you get, the lower levels of vitamin D in the general population tend to be. Other geographical studies have found countries on the same latitude as Northern Scotland also have higher than average rates of MS.
This well-conducted study builds on previous work and could offer some important clues as to the origins of this disease and whether any genetic or environmental factors play a role.
Where did the story come from?
The study was published in the peer-reviewed Journal of Neurology, Neurosurgery and Psychiatry. It was funded by the Scottish government.
It was covered fairly by the papers, although the Daily Mail’s link between the origins of MS and the Vikings, accompanied by a comic photo, was a little over the top. The study does not mention Vikings, and in fact, the paper seems to imply that the rise in prevalence is more likely due to environmental factors than genetics.
However, it does suggest that a ‘gene-environment’ interaction may be the cause, while comments by the authors have reportedly linked the Orkney Islands’ high multiple sclerosis rates it to its Scandinavian history.
While the media coverage of the study does discuss vitamin D exposure as a possible environmental risk factor, other factors that are discussed in the study include exposure to a viral infection, such as the Epstein-Barr virus (the virus that causes glandular fever).
Finally, and somewhat oddly, the study has made today’s news sources despite being published in May 2012. It is unclear why it has taken seven months for the study to hit the headlines.
What kind of research was this?
This was a study of the prevalence of multiple sclerosis in three areas of northern Scotland: Orkney, Shetland and Aberdeen. The prevalence of a disease is the proportion of people who have it within a given population at any given time. This is different from the incidence, which is the number of newly diagnosed cases of a disease within a specific period – normally a year.
Multiple sclerosis is a progressive disease affecting nerves in the brain and spinal cord, causing problems with muscle movement, balance and vision. The cause is unknown.
The current thinking is that MS is likely to arise from a complex interaction of both environmental and genetic factors.
There is currently no cure, although treatment can delay symptoms.
The researchers say that very high multiple sclerosis prevalence rates were recorded in northern Scotland 30 years ago. In particular, between the 1950s and 1980s, studies in Orkney and Shetland showed a steady rise in prevalence to about 190 per 100,000 (about 0.19%), while similar increases were found in Aberdeen and north east Scotland. These were age and gender specific rates and standardised to the Scottish population, meaning that there were minor adjustments to the numbers to allow for direct comparison between the three areas.
There have been no prevalence studies of MS in northern Scotland since the early 1980s, despite this area having one of the highest rates of MS in the world.
This new study aimed to measure current prevalence rates in Aberdeen, Orkney and Shetland, among men and women and among different age groups. The researchers aimed to assess whether the rates had changed over time and to determine which factors might be an influence.
What did the research involve?
In 2009, the researchers searched the records of hospitals, general practices and laboratories in the relevant areas to identify MS patients who were alive, residing in the study area and registered with a participating general practice.
All GPs in Aberdeen, Orkney and Shetland were approached. All appropriate doctors involved in the care or diagnosis of patients with MS were informed of the project by letter. The number in each area’s general population was calculated using GP data.
Researchers identified MS patients by a number of methods. They searched GP databases for patients registered on the relevant day (September 24 2009) with a specific MS diagnostic code. They also searched hospital discharge data using a diagnostic code, MS specialist nurse databases and relevant hospital laboratory results. The project was supported and advertised by MS patient organisations.
A neurology specialist reviewed all hospital and GP records and laboratory data of all patients identified by the searches to confirm the diagnosis according to internationally accepted criteria.
Patients were included if they satisfied one set of established criteria for clinically ‘definite’ or ‘probable’ and laboratory supported ’definite’ or ‘probable’ MS. In cases of doubt, a senior neurologist made the final decision.
Researchers also recorded different MS subtypes and whether and how patients were disabled, using established disability scales. They also used a national index of multiple deprivation to analyse patients’ economic status.
They sent out a subsequent postal questionnaire to those MS patients considered suitable, asking further about:
- levels of disability
- place and date of diagnosis (to identify those who migrated into the area after diagnosis)
- employment status
The researchers calculated age-gender specific prevalence rates and standardised these to the Scottish population. This allows them to directly compare populations with different age structures with each other and gives an overall expected rate as if the population in these cities and islands were the same as those in Scotland as a whole.
Researchers say they expected to find 480 MS patients in the areas studied, based on previous prevalence of about 190 per 100,000. This would give sufficient statistical power to detect any increase in prevalence over time (that is, any increase detected would be highly unlikely to be the result of pure chance).
What were the basic results?
The researchers identified 590 patients (420 women and 170 men) who satisfied diagnostic criteria for MS. There were 442 patients from Aberdeen, 82 from Orkney and 66 from Shetland.
The average age was 53 years and on average, they had had the disease for 19.4 years.
Using one set of diagnostic criteria, the researchers found that prevalence rates for probable or definite MS per 100,000 were:
- Combined area – 248 (95% confidence interval (CI) 229 to 269)
- Orkney – 402 (95% CI 319 to 500),
- Shetland – 295 (95% CI 229 to 375)
- Aberdeen – 229 (95% CI 208 to 250).
Another set of diagnostic criteria, that made use of a more stringent set of criteria, gave a lower prevalence of 202 (95% CI 198 to 206). The researchers also found that:
- prevalence of MS was highest in women (female:male ratio of 2.55:1, 95% CI 2.26 to 2.89) with about 1 in 170 women in Orkney affected
- prevalence was lowest in the most deprived socioeconomic group
- 45% of the patients had significant disability
To put these figures in some sort of context, the prevalence of MS of the United States (at the upper limit of the range of estimation) is 95 per 100,000 – so rates in Orkney are four times higher.
How did the researchers interpret the results?
The researchers say that the prevalence of MS has increased in the overall area, most markedly in Orkney, then Shetland, over the past 30 years. For example, the difference in prevalence between the 1980s and the year of the study was 37 per 100,000 for the whole area and 186 per 100,000 for Orkney.
They say the increase could be due to a number of factors, but the most likely cause is rising incidence (the number of new cases being diagnosed each year), influenced by gene-environment interaction.
They point out that Orkney has the highest prevalence rate recorded worldwide. However, the disproportionate rise in the northern islands may be the result of random fluctuation in small populations. The smaller a sample is, the more likely it is to give a skewed result – toss a coin five times in a row and you might get four heads – toss it 500,000 times in a row and you’re likely to get a 50/50 split between heads and tails.
In their discussion, the researchers say that a rise in incidence over such a short period cannot be accounted for by genetic factors alone and that an environmental factor is likely to be involved.
They point out that recent evidence has suggested a significant role for vitamin D in the development of MS and changes in vitamin D levels may play a role, although the study did not measure vitamin D levels.
They also mention other theories, suggesting the higher MS prevalence among higher socioeconomic groups may be due to:
- these groups having less immunity to viruses implicated in the development of MS (the hygiene hypothesis)
- less exposure to sunlight, which is needed for the skin to make vitamin D and linked to a vitamin D theory of MS causation
This was a well-conducted study which carried out a thorough review of medical and laboratory records to verify each diagnosis of MS, and used internationally accepted criteria to establish the prevalence of MS (although prevalence rates for the study did vary according to different diagnostic criteria).
However, as the authors point out, most patients were not reviewed in person by the study team, so it is possible there were some inaccuracies. In particular, a number of older people who were diagnosed with MS before the widespread introduction of MRI scans to help diagnose the disease more accurately, may have had other nervous system diseases.
Further research is required to find out the reasons for high rates of MS in northern Scotland and the recent increase in prevalence indicated by this study.
The researchers are now working on ongoing research looking at vitamin D levels in people living in Orkney. We look forward to reading their results with interest.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Mail, 10 December 2012
The Guardian, 10 December 2012
BBC News, 11 December 2012
ITV News, 10 December 2012
Links to the science
Journal of Neurology, Neurosurgery & Psychiatry. Published online May 10 2012