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Sun Exposure and Vitamin D During Pregnancy May Reduce Children's Risk of Multiple Sclerosis

Renee DespresFriday, June 15, 2012 - 20:41

Pregnant women who spend time in the sun or take vitamin D supplements may lower their children's risk of developing multiple sclerosis (MS) later in life, a preliminary study suggests.

Guiulio Disanto, MD, of the University of Oxford, England, reported these results in a poster presentation at the annual meeting of the American Academy of Neurology (AAN) on April 13.

Story Highlights
  • This preliminary study suggests that when women are exposed to sun during pregnancy, their children are less likely to develop multiple sclerosis later in life.
  • This study calls into question the results of a previous study that showed sun exposure was most important, in terms of children's risk of MS, during the first trimester of pregnancy. In this study, the second and third trimesters of pregnancy were key periods for sun exposure.
  • MS rates also increased in children who were born to women with low levels of vitamin D during the late stages of pregnancy.
  • This study was presented at a conference and published as an abstract. Data and conclusions should be considered preliminary until and unless it is published in a peer-reviewed journal.
  • These results are based on a retrospective analysis and do not prove that lack of UV exposure in late pregnancy causes multiple sclerosis.
  • These findings may help women and their doctors make decisions about vitamin D supplementation during pregnancy.

For the retrospective study, the research team gathered weather satellite data indicating monthly average ultraviolet (UV) levels. They then compared those data to the birth dates of more than 20,000 MS patients – and more than 2 million people without MS – in the United Kingdom. Mothers who had relatively high UV exposure during the second and third trimesters were significantly less likely to deliver children who were later diagnosed with multiple sclerosis. Conversely, MS rates increased in children who were born to women with low levels of vitamin D during the late stages of pregnancy.

More Evidence for Vitamin D

Several other studies have linked low levels of vitamin D during pregnancy to increased risk of MS in their children later in life. An Australian research team reported similar results in 2010. However, results of the Australian study suggested that the important time for exposure to sunlight was the first trimester of pregnancy. The British researchers found that the second and third trimesters were the key period for sun exposure.

What is Vitamin D?

Vitamin D is a a fat-soluble steroid vitamin that increases the absorption and metabolism of calcium and phosphorous. It is is made by the body in response to sun exposure. Low vitamin D levels can occur either because of lack of sun exposure or lack of vitamin D in the diet.

It was unclear why the two studies did not agree on the timing of sun exposure and risk of MS, Disanto said. However, the researchers used different methodologies to arrive at their conclusions.

To estimate mothers' UV exposure during pregnancy, the Australian researchers compared birth months to climatological averages over a 26-year period. Disanto and colleagues, on the other hand, gathered weather satellite data tracking monthly average UV exposure in Great Britain during the years study participants had been born, 1979 to 1992.

Then they compared those data to months of pregnancy for 11,282 MS patients diagnosed from 1997 to 2009 and more than 2 million people without MS in Scotland, plus 8,702 cases and about 20,000 controls in England and Wales who had died from 1971 to 1991. The researchers also used data from two previous studies about levels of vitamin D in the blood of about 3,400 women in England and Wales and 354 in Scotland.

Results: More Sun Late in Pregnancy, Less Multiple Sclerosis

MS was diagnosed more frequently in people who were born during spring months – when their second and third gestational trimesters were in the winter months. Geography also played a role. In the northernmost areas of the U.K. MS rates were highest in people born during April and May and lowest in people born in September. For people born in the more southerly England and Wales, MS risk was highest in May and lowest in November and December.

These results corresponded to significant increases in MS risk with the lowest UV exposure during the fourth to seventh months of pregnancy in Scotland and the third to sixth months in England and Wales. MS risk was also highest when children were born to mothers with low vitamin D levels during the fifth to eighth months of pregnancy in England and Wales. In Scotland, higher rates of MS were seen among children born low vitamin D levels during the final months of pregnancy in Scotland.

What it Means

This study adds to the growing body of evidence that low sun exposure and and low levels of vitamin D increase MS risk. Researchers identified the second and third trimesters of pregnancy as key periods for UV exposure and vitamin D. “A correct understanding of the timing of vitamin D action on fetal development will be extremely relevant for future strategies of disease prevention,” researchers wrote.

These findings do not mean that pregnant women should start sunbathing – or move to the tropics during the winter months. Ultraviolet radiation from the sun has been clearly established as the main cause of skin cancer. However, this information may help women and their doctors make decisions about vitamin D supplementation during pregnancy. Women can also increase their intake of vitamin D through dietary sources. Although few foods naturally contain high levels of vitamin D, the vitamin is added to many frequently-consumed foods.

Dietary Sources of Vitamin D

Very few foods are naturally high in vitamin D. However, several foods are commonly fortified with vitamin D. Here are a few choices.

Foods with naturally-occurring vitamin D include:

  • Fatty fish (salmon, mackerel, tuna fish, sardines)
  • Cod liver oil
  • Beef liver
  • Eggs

Foods commonly fortified with vitamin D include:

  • Milk (nonfat, reduced-fat, and whole)
  • Orange juice (if the label says it has been fortified with vitamin D)
  • Margarine
  • Yogurt
  • Cheese
  • Ready-to-eat cereal

References

Disanto G, et al "Gestational ultraviolet and vitamin D exposure and the risk of multiple sclerosis in the United Kingdom" AAN 2011; Abstract P05.289.

National Institutes of Health, Office of Dietary Supplements. Dietary supplement fact sheet: Vitamin D. Last update 2/25/2011. Available at http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/