Sun exposure in youth can protect against multiple sclerosis
People who spend a lot of time outdoors in their teens run just half the chance of contracting multiple sclerosis (MS) later, according to a Norwegian study.
A new study from Bergen has shown that persons who spent little of their adolescence outdoors run a higher risk of MS in their 40s than those got more sunlight. Multiple sclerosis is a chronic disease that affects the central nervous system.
Increased outdoor activities as a youth have been linked to a lower risk of MS.
“Our days of youth are a sensitive period for exposure to environmental factors that can be pivotal regarding who gets MS,” says Dr Kjetil Lauvland Bjørnevik at the University of Bergen.
Especially 16 to 18-year-olds
Persons who were outdoors the least in their youth ran nearly twice the risk of MS later on. Norwegian researchers discovered this by charting the teenage lifestyles of healthy persons and MS patients.
Apparently, adults cannot compensate for their bygone teenage years indoors by later becoming sun-loving men and women who spend lots of time outdoors.
The outdoor-indoor links to the disease among Norwegians covered by the study appeared to be greatest when they were aged 16 to 18.
Spending time outdoors had less of a protective effect once adulthood is reached.
Scientists are not certain whether the positive factor protecting against MS is vitamin D or something else.
Too much sunblock can be a risk
The researcher asked the participants how much sunblock they used when they were children and teenagers. Those who smeared on a lot of it, and more often, had the highest risk – like those who spent the most time indoors.
“It looks like extensive use of sun lotions with higher sunblock in childhood hinder this protection,” explains Bjørnevik.
Do you think we should be careful not to protect our kids with too much UV sunblock?
“We mustn’t dismiss the advice about use of sunblock on the basis of a single study like this. The healthy habit of avoiding being sunburned is vital for protecting against diseases that are more common than MS. But the findings do show that there is something about sunlight which probably is important regarding the later development of MS,” says the medical researcher.
Redheads at risk
Redheads can also be more at risk of MS than others.
This has been seen earlier, but the researchers have not known why.
“Persons who are sensitive to sunlight might behave in ways that diminish their vitamin D intakes. They either don’t spend enough time in sunlight or they use too much sunblock,” says the researcher.
Another study has shown that other methods of getting vitamin D dosages can also protect against MS.
“It shows that those who have taken a lot of cod liver oil or have the highest intakes of fatty types of fish are also those with the lowest MS risks,” Bjørnevik says.
Both studies showed it to be especially important to get sufficient doses of vitamin D when 16 to 18 years old.
Especially in the summer
The researcher has tallied and compared outdoor activities to estimate how much sun and vitamin D teenagers exposed themselves to.
The sample in this study consisted of participants from Norway and Italy.
Amongst the Norwegian participants, the clearest link between low prevalence of MS and lots of outdoor activities was seen for summer activities rather than winter ones.
“This indicates that vitamin D is a vital factor, as you don’t get the vitamin from being outdoors in Norway in winter,” says Bjørnevik.
Another study has shown the vitamin D can also deter the progress of MS when the disease is diagnosed in an early stage.
Different in Italy
Outdoor activities among the Italian participants had the greatest positive effect at a much younger age, in the first five years of life.
Spending time outdoors there, so much further south, appeared to protect against MS in both summer and winter.
The researchers found that exposure to environmental factors as an adult also seemed to be important for the Italian participants.
Smoking and mononucleosis
Medical researchers have been studying environmental factors that can contribute to higher risks of MS for decades.
However, less research has been conducted which might reveal underlying factors for why some get the disease and some don’t.
In addition to the recent link seen regarding sunlight exposure, environmental factors such as smoking, infections, mononucleosis and obesity have also been found to raise the risk of MS.
“Smoking does not seem to be such an age-related risk factor as sunlight or vitamin D,” says Bjørnevik.
Bjørnevik’s study was included in his doctoral thesis, working with the University of Bergen’s Department of Global Health and Primary Care and Haukeland University Hospital’s Norwegian Multiple Sclerosis Competence Centre. A professor from the University of Ferrara, Italy acted as his advisor.
Read the Norwegian version of this article at forskning.no
Translated by: Glenn Ostling
- Abstract: Kjetil Lauvland Bjørnevik: The interplay between environmental risk factors for multiple sclerosis. Doctoral dissertation, 28 April 2017.
- Abstract: K. Bjørnevik et al.: Sun exposure and multiple sclerosis risk in Norway and Italy: The EnvIMS study. Multiple Sclerosis Journal, 10 January 2014.