This report is part of a 12-month Clinical Context series.
By Richard Robinson, Contributing Writer, MedPage Today Published: June 04, 2010
Reviewed by Ari Green, MD; Assistant Professor, University of California, San Francisco.
- Explain to interested patients that childhood exposure to sunlight, or vitamin D intake, may influence the age at which MS symptoms begin.
- Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
SAN ANTONIO — Age of onset of multiple sclerosis was more than two years earlier in patients who lived in northern latitudes — with reduced exposure to the sun in fall and winter — during childhood, researchers found.
Low intake of vitamin D supplements was also associated with earlier onset, according to Joel Culpepper, MD, of the University of Maryland School of Medicine in Baltimore and colleagues.
"This is the first evidence that low sun exposure may be related to early onset of of MS symptoms," Culpepper told attendees at the meeting of the Joint Consortium of Multiple Sclerosis Centers and America's Committee on Treatment and Research in Multiple Sclerosis.
Low sun exposure has long been linked to the risk of MS, based on geographic and ethnic patterns in differential MS incidence. To determine if the same was true for age of onset, Culpepper and colleagues recruited 1,167 men and women drawn from the Veterans Administration's Multiple Sclerosis Surveillance Registry for an extensive interview to determine how much time they spent out in the sun during the fall and winter between the ages of 6 and 15.
Combined with their ZIP code and altitude, this information allowed the researchers to determine the total UV-B exposure during those months.
Vitamin D supplement intake was determined by participants' recollection of milk, fish, and cod liver oil consumption.
The group of participants was about half women, and included 948 patients with relapsing-remitting MS and 219 with primary progressive form of the disease.
No effect of sun exposure or vitamin D intake was seen in those with primary progressive disease, and no effect was seen in patients with either form who lived in areas of the country that got a lot of sunlight in the winter months. "If you live in a high solar radiation area, such as the deep South, you are probably getting enough exposure even in the deep winter," Culpepper said.
But in those with relapsing-remitting MS who lived in more northern areas, those in the lowest quartile of exposure, with less than 16 weeks of cool-season exposure, had an age of onset 2.3 years before those in the highest three quartiles (P=0.01).
Age at onset was delayed by three years for regular users of cod liver oil (P=0.01), a potent source of readily available vitamin D. In a multiple regression model, that effect was more pronounced in low-solar radiation areas.
"The link between age of onset and sun exposure is likely through the effect of sun on vitamin D," Culpepper said.
Childhood through puberty is a critical period of MS risk, he noted. "We believe there is a window of susceptibility" up to the early or mid-teens.
"We need to be able to identify the at-risk individuals, and then intervene in childhood," he said, but noted that risk is likely to be a combination of genetic, in utero, and childhood effects.
"This is a big challenge for epidemiologists to work out."
Intervention would be another challenge, he pointed out, since increasing sun exposure without protecting against sun burn increases risk of melanoma. Vitamin D supplementation would be an alternative, Culpepper suggested.
Culpepper had nothing to disclose.
McDowell had nothing to disclose.
Primary source: 2010 CMSC Scientific Abstract Book
McDowell TC, et al "Past sun exposure, vitamin D intake and age at onset among veterans with multiple sclerosis" 2010; 131.