Scientists have been studying vitamin D levels in relation to the development of many chronic disorders — from breast cancer to multiple sclerosis (MS) — for quite some time now. Vitamin D, known as the “sunshine vitamin” due to our skin’s ability to glean it from the sun’s UV rays, can affect up to 2,000 genes in the body and plays a large role in maintaining the immune system.

In a new study published in JAMA Neurology, researchers from the Harvard T.H. Chan School of Public Health once again examined the link between vitamin D and MS, this time finding that pregnant women who had a vitamin D deficiency may increase their child’s risk of developing MS. Past research has linked proper vitamin D levels with protection against the autoimmune disorder, and while research is still ongoing, researchers are fairly certain there is a link between vitamin D and MS. A 2015 study conducted by researchers at Johns Hopkins University School of Medicine even found that high doses of vitamin D could help the immune systems of MS patients, though other researchers argue that too much vitamin D can harm our health.

The latest study primarily examines the role of vitamin D supplementation during pregnancy determining MS risk. The researchers studied 193 people, 163 of whom were female and had been diagnosed with MS. All of the participants’ mothers had been a part of the Finnish Maternity Cohort, a study during which they provided maternal blood samples to measure serum 25-hydroxyvitamin D, known as 25(OH)D — a biomarker for bone problems or disorders typically involved with vitamin D deficiency.

Most of the women received this test during their first trimester, and it found their average vitamin D levels were insufficient. The researchers found that children born to mothers with vitamin D deficiencies during pregnancy had a 90 percent higher risk of MS as an adult. This is a huge number to report, but the researchers note that 25(OH)D tests may not be the most accurate marker for MS, and also state that past studies found no link between vitamin D deficiency during pregnancy and MS.

The Multiple Sclerosis Society UK notes that people should be careful before assuming that vitamin D is directly linked to MS. On its website, the organization states that it “remains an active area of research with a number of unanswered questions.”

When it comes to pregnancy, the MS Society writes, “The evidence isn’t conclusive and more research needs to be carried out to determine whether vitamin D levels during pregnancy could influence the risk of the child developing MS later in life.” They go on to note that it’s tough to determine how vitamin D supplementation could act as a treatment, because many studies “use different doses and forms of the vitamin, and are often not carried out to a reliable standard, so there is still not enough evidence to tell us whether vitamin D supplementation is an effective and also safe treatment for MS.”

In addition, too much vitamin D could lead to a variety of health problems related to high blood calcium, including nausea, kidney stones, cardiovascular issues, and constipation.

“[W]hile our results suggest that vitamin D deficiency during pregnancy increases MS risk in the offspring, our study does not provide any information as to whether there is a dose-response effect with increasing levels of 25(OH)D sufficiency,” the authors wrote. “Similar studies in populations with a wider distribution of 25(OH)D are needed.”

Source: Munger K, et al. JAMA Neurology. 2016.