Are vitamin D supplements safe during pregnancy?

I find this very difficult myself. I really don’t like to be in the position of advising people to do something their doctor has told them not to do, and I wouldn’t expect you to do that. I can only present the information that is out there, and let you make up your own mind.

The important thing about this question is that it is more about the risk of the child developing MS as an adult, and much less about your health, because pregnancy is very protective for you. As you know, children of people with MS have around 30x to 40x the risk of getting MS as others in the population. That is a very high risk. Vitamin D supplementation during pregnancy is recommended to lower that risk.

In my view, the evidence now is very clear that vitamin D supplementation lowers the risk of getting MS throughout life. This has been shown in a number of studies, including the Nurses Health Study. The evidence base around supplementation in utero is growing rapidly. There has been much published about the risks of developing MS related to season of birth. One paper on this was published in Melbourne, from the Murdoch Children’s Research Institute, from Anne-Louise Ponsonby’s group. Click here for the link to the full paper.

Their last paragraph sums up the situation well:

“The findings here provide the first population based evidence beyond month of birth patterns to indicate that vitamin D supplementation for the prevention of multiple sclerosis might also need to be considered during in utero development.”

Chaudhuri, a Glasgow neurologist, was probably the first to strongly advocate this in 2005:

Med Hypotheses. 2005;64(3):608-18.
Why we should offer routine vitamin D supplementation in pregnancy and childhood to prevent multiple sclerosis.
Chaudhuri A.
Department of Neurology, Institute of Neurological Sciences, 1345 Govan Road, Glasgow G51 4TF, [email protected]

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system that runs a chronic course and disables young people. The disease is more prevalent in the geographic areas that are farthest from the equator. No form of treatment is known to be effective in preventing MS or its disabling complications. A number of epidemiological studies have shown a protective effect of exposure to sunlight during early life and a recent longitudinal study confirmed that vitamin D supplementation reduced life-time prevalence of MS in women. Very little is known regarding the role of vitamin D on the developing brain but experimental data suggest that cerebral white matter is vitamin D responsive and oligodendrocytes in the brain and spinal cord and express vitamin D receptors. It is possible that differentiation and axonal adhesion of oligodendrocytes are influenced by vitamin D level during brain development and a relative lack of vitamin D may increase oligodendroglial apoptosis. The age effect of migration on susceptibility to develop MS could be explained by a role of vitamin D on brain development. In areas of high MS prevalence, dietary supplementation of vitamin D in early life may reduce the incidence of MS. In addition, like folic acid, vitamin D supplementation should also be routinely recommended in pregnancy. Prevention of MS by modifying an important environmental factor (sunlight exposure and vitamin D level) offers a practical and cost-effective way to reduce the burden of the disease in the future generations.

In my view, the only question is what dose of vitamin D one should take. Many neurologists are not really familiar with dosages for vitamin D supplementation, as they do not use this in any of the other neurological diseases they manage. There is also a widespread irrational fear in medicine about overdosage of this naturally occurring hormone. Consider this: if you step outside in any warm city in summertime with only a bathing suit on for around five minutes at midday, you will make 15,000IU of vitamin D immediately. Why would you be told not to take 1,000IU? How could that be toxic?

This is probably one of the few papers that really make a recommendation about doses during pregnancy.
Hollis is one of the world experts on vitamin D. PubMed him and you will find he has published 202 papers on vitamin D in the world’s best journals. The abstract is as follows:

J Bone Miner Res. 2007 Dec;22 Suppl 2:V39-44.
Vitamin D requirement during pregnancy and lactation.
Hollis BW.
Department of Pediatrics, Division of Pediatric Nutritional Sciences, Medical University of South Carolina, Charleston, South Carolina, USA.

The current recommended dietary requirement for vitamin D intake (200 IU/d) during pregnancy and lactation is based on little, if any, scientific evidence, and as a result is clinically irrelevant with respect to maintaining nutritional vitamin D status during these demanding human conditions. Current research has shown that the actual dietary requirement during pregnancy and lactation may actually be as high as 6,000 IU/d. Current data on which these new recommendations could be based are presented.

Dr Jonathan White MBChB MRCOG