November 11, 2010 — Women with multiple sclerosis with low vitamin D levels during pregnancy and breast-feeding are not at significant risk for postpartum relapses, report researchers.
The findings suggest the recommended dose of vitamin D supplementation during pregnancy and breast-feeding should be the same for women with multiple sclerosis as for those who do not have autoimmune disease.
The results were published online November 8 in the Archives of Neurology. Investigators studied 28 pregnant women with multiple sclerosis. They prospectively followed-up patients through the postpartum year using structured interviews to assess exposures and symptoms. The researchers measured serum 25-hydroxyvitamin D levels during the third trimester and 2, 4, and 6 months after the women gave birth.
Half of the women, a total of 14, breast-fed exclusively, and 12 women relapsed after giving birth. During pregnancy, the average blood levels of 25-hydroxyvitamin D were 25.4 ng/mL and fluctuated with the season (P = .009).
After birth, levels remained low among women who were exclusively breast-feeding. By 4 and 6 months after childbirth, vitamin D levels were an average of 5 ng/mL lower among women who breast-fed exclusively than among women who did not (P = .001).
However, these low postpartum vitamin D levels were not associated with risk for multiple sclerosis relapse. "If anything," reports the team led by Annette Langer-Gould, MD, from Kaiser Permanente Southern California, in Pasadena, "by 3 to 6 months after childbirth, 25-hydroxyvitamin D levels were marginally higher among the women who relapsed within the first 6 months after childbirth compared with women who were relapse free during the corresponding period."
Paradoxical Finding
The investigators say they do not believe that higher vitamin D levels increase the risk for postpartum relapses. "The rise we observed did not appear to occur prior to the onset of symptoms and the findings were of marginal statistical significance after accounting for season. Instead," they explain, "we think this apparent inverse association is a reflection of the fact that most of the women who relapsed in the study also did not breastfeed or did so only briefly."
A new study published in October in Genome Research showed biologic evidence that vitamin D may protect against autoimmune diseases and certain cancers (2010;20:1352-1360).
The new genetic analysis suggests that vitamin D interacts with genes specific for multiple sclerosis, type 1 diabetes, colorectal cancer, and other diseases, reports Oxford University genetic researcher Sreeram Ramagopalan, PhD.
"Genes involved in autoimmune disease and cancer were regulated by vitamin D," he said during an interview when the study was first published. "The next step is understanding how this interaction could lead to disease."
On the surface, the authors of this new study point out, these findings may seem inconsistent with previous studies suggesting an association between low serum vitamin D and multiple sclerosis. "However," they note, "our findings seem logical when other lines of evidence are considered."
Other Factors at Play
First, it is well known, the researchers explain, that women who are pregnant or lactating are at high risk for hypovitaminosis D. Second, it is also well established that pregnant women with multiple sclerosis have a low risk for relapse and that lactation does not increase the risk.
Third, they note, there is no evidence that the hormonal effects of pregnancy or lactation are different in those women with multiple sclerosis compared with healthy women. Finally, dark-skinned people are at higher risk for vitamin D insufficiency, yet have a lower risk for multiple sclerosis than white people. This suggests that low vitamin D level in isolation is not always associated with increased risk, Dr. Langer-Gould and colleagues conclude.
"Low vitamin D in isolation is not an important predictor of postpartum multiple sclerosis relapses," they note. "Other factors associated with pregnancy and lactation may be important modulators of the relationship between vitamin D and disease activity."
This study was supported by the National Institute of Neurologic Disorders and Stroke and a Wadsworth Foundation Young Investigator's Award. The researchers have disclosed no relevant financial relationships.
Arch Neurol. Published online November 8, 2010. Abstract
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