Doubling Up on Vitamin D When Eating for Two?

Thursday, August 11, 2011

When a woman is pregnant and ‘eating for two,’ it makes sense to increase the amount of nutrients consumed so there is enough nutrition for both the mother’s increased metabolism and the developing fetus. Does this thinking apply to vitamin D as well? Back in 1997, the Institute of Medicine (IOM) recommended that pregnant women consume 200 IU of vitamin D per day during pregnancy which is the same amount they recommended for everyone else. The latest guidelines from the IOM, which were just published in 2010, list the Estimated Average Requirement (EAR) and the Recommended Dietary Allowance (RDA) for pregnant women as 400 IU/day and 600 IU/day respectively. Again, the current recommendations are the same for everyone whether you are a one year old child, a 60 year old man or a 29 year old pregnant woman. Is it really advisable for a pregnant woman to get the same amount of vitamin D as a one year old child?

A brave group of researchers at the Medical University of South Carolina (MUSC) in Charleston, SC set out to begin to answer this question. They were given permission to conduct a study that supplemented pregnant women with up to 4000 IU of vitamin D per day as long as the study had very stringent safety guidelines in place. The study, surprisingly, began in 2004 when the IOM still suggested that pregnant women only need to consume 200 IU of vitamin D per day for a healthy pregnancy. The study at MUSC was designed very well and divided the participants into three randomized groups. One group took a prenatal multivitamin which contained 400 IU of vitamin D and a placebo capsule with 0 IU of vitamin D for a total intake of 400 supplemental IU of vitamin D per day. The second group took a prenatal multivitamin with 400 IU of vitamin D and a capsule with 1600 IU of vitamin D for a total of 2000 IU of supplemental vitamin D per day. The third group took a prenatal multivitamin with 400 IU of vitamin D and a capsule with 3600 IU of vitamin D for a total of 4000 IU of supplemental vitamin D per day.

The vitamin D supplementation began between weeks 12 and 16 of pregnancy and continued until delivery. At the conclusion of the study in 2010, the researchers analyzed the data from the 350 study participants and determined that it is quite safe to consume 4000 IU of vitamin D during pregnancy (after week 12). To quote the investigators: “Not a single adverse event was attributed to vitamin D supplementation or circulating 25(OH)D [(vitamin D)] levels.” The researchers also concluded that daily supplementation with 4000 IU is the most effective way to achieve sufficient serum levels of circulating vitamin D during pregnancy in all ethnicities. It is interesting to note that the study was conducted in the Southeastern US where high quality sunshine is plentiful. Therefore, it is possible that pregnant women in areas that get less quality sunshine might need to supplement with even higher doses of vitamin D as noted by the investigators. The investigators did speculate about the benefits of sufficient serum vitamin D levels but did not come to any definitive conclusions since the study only looked at safety rather than long-term beneficial effects. In general, adequate vitamin D levels could have beneficial effects on the cardiovascular system, the immune system, the musculoskeletal system and endocrine function.

So yes, when ‘eating for two’ it is safe to say that women need to double, triple, quadruple up on the vitamin D! A good way to approach vitamin D supplementation is to monitor your own serum levels especially during pregnancy. The authors of the study discovered that pregnant women should maintain serum levels of at least 30 ng/mL (75 nmol/L) but ideally 40 ng/mL (100 nmol/L). Vitamin D is found in salmon (sockeye), mackerel, tuna fish, egg yolk, mushrooms that have been exposed to the sun, fortified orange juice, cereal and milk. Be aware, though, that most fish contain mercury so it is not advisable for pregnant women to consume fish every day. Also, as a side note, cod liver oil is normally a good source of vitamin D but it contains very high amounts of vitamin A which can be harmful during pregnancy.


Laura Firetag ND Student Bastyr University

Hollis, Bruce, et al. "Vitamin D Supplementation During Pregnancy: Double Blind, Randomized Clinical Trial of Safety and Effectiveness." Journal of Bone and Mineral Research. (2011): 1-52 (link to pdf)

Labels: D3, pregnancy, sun, sunlight, sunshine, supplementation, vitamin D

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Doubling Up on Vitamin D When Eating for Two?

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