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Living in sunny climates may lower risk of multiple sclerosis

People who live in sunnier climates are far less likely to develop multiple sclerosis later in life, a new study suggests.

A study by researchers from the University of British Columbia in Vancouver, Canada, found that higher exposure to sun between ages five and 15 reduced the risk of MS by 55 percent.

MS is an autoimmune disease affecting about 400,000 Americans that wreaks havoc on the central nervous system causing weakness, pain and loss of motor control. 

This study builds on previous research tying sun exposure its impact on vitamin D levels to the debilitating disease for which there is no known cause or cure.

A new study suggests women who lived in sunnier climates have half the risk of developing MS of those with less sun exposure. Northern states have nearly twice as many cases of MS than southern states, possibly because they are further from the equator and get less sun

In people with MS, the immune system attacks the protective myelin covering surrounding tissue in the central nervous system, which is made up of the brain, spine and optic nerves.

Scar tissue forms around the nerve fibers in place of the damaged myelin and interferes with brain signals through the spinal cord.

Most people are diagnosed between the ages of 20 and 40. Early symptoms can include vision problems, tingling and numbness in the legs or feet and weakness or fatigue. 

MS episodes, characterized by new or worsening symptoms, typically increase in frequency and intensity with age. 

MS occurs twice as often in women than in men and people of Northern European descent have the highest risk, regardless of where they live.

Previous studies have linked sun exposure to a lower risk of MS, particularly through levels of vitamin D, which is absorbed through the sun’s rays.

In fact, according to the Multiple Sclerosis Foundation, northern states that are further from the equator and thus have less sun have double the rate of MS cases than southern states. 

This was the first study to look how differences in sun exposure duration and intensity throughout one’s lifetime are related to MS.

‘We found that where a person lives and the ages at which they are exposed to the sun’s UV-B rays may play important roles in reducing the risk of MS,’ said study author Helen Tremblett, who has a PhD in pharmacoepidemiology.

The study published Wednesday in the American Academy of Neurology’s journal Neurology is based on data from 151 women with MS and 235 women of a similar age without MS.

The participants represent a variety of climates and locations across the US and each filled out a survey about their summer, winter and lifetime sun exposure. 

The women were divided into three groups, low, moderate and high UV-B ray exposure based on where they lived. 

The results showed that women in pre-MS onset age groups who lived in sunnier climates with the highest exposure to UV-B rays had 45 percent reduced risk of developing the disease when compared to those living in areas with the lowest UV-B ray exposure.

Possible causes of MS 

There is no specific known cause for MS, but experts believe it’s likely influenced by a mix of genetics and environmental and lifestyle factors.

Some of the factors that have been suggested as possible causes include:

Your genes 

MS isn’t directly inherited, but people who are related to someone with the condition are more likely to develop it; the chance of a sibling or child of someone with MS also developing it is estimated to be around 2-3%.

Lack of sunlight and vitamin D 

MS is more common in countries far from the equator, which could mean that a lack of sunlight and low vitamin D levels may play a role in the condition, although it’s not clear whether vitamin D supplements can help prevent MS


People who smoke are about twice as likely to develop MS compared to those who don’t smoke.

Viral infections

It has been suggested that infections, particularly those caused by Epstein-Barr virus (responsible for glandular fever), might trigger the immune system, leading to MS in some people.

Source: NHS Choices 

Those who lived in areas with the highest levels of UV-B rays between ages of five and 15 had a 51 percent reduced risk of MS compared to the lowest group.

Additionally, those who had spent more time outdoors in summer in locations with the highest exposure between ages five and 15 had a 55 percent lower risk of developing the disease than those in the lowest-exposure group.

Of the participants already diagnosed with MS, 22 percent had high sun exposure between five and 15 years old while 41 percent had low exposure in that period.

They also tended to have lower rates of exposure later in life. 

‘Our findings suggest that a higher exposure to the sun’s UV-B rays, higher summer outdoor exposure and lower risk of MS can occur not just in childhood, but into early adulthood as well,’ said Tremlett. 

A growing body of research suggests that identifying and correcting vitamin D deficiencies early could aid in early treatment of the disease.

A 2013 study from Harvard found that people with early-stage MS who had higher levels of vitamin D had better outcomes during five-year follow-up appointments.  

Findings from a 2008 study by the New Jersey Medical School and a 2009 study by the University of Oxford both suggest that vitamin D may have a protective effect that reduces the risk of developing MS. 

Another study from the Netherlands suggested that vitamin D may lessen the frequency and severity of symptoms in people who already have MS.    

The study authors noted that one of the study’s limits was that time spent in the sun was self-reported and based on memories that may not be entirely accurate.

However, the data for UV-B exposure was captured using place of residence, which is less likely to be influenced by such factors.

Additionally, all of the participants were female and 98 percent were white, so the results may not apply to other populations.