The importance of vitamin D supplementation during pregnancy is easily overlooked. Many people think that they can get enough vitamin D from the sun; however, they often neglect the factors influencing vitamin D via sun exposure. According to the analysis of the national nutrition and health data of the Ministry of Health and Welfare by professor Mei-Xuan Li from the School of Public Health, National Defense Medical Center, up to 98% of people have insufficient vitamin D concentration in the blood (the standard is 33μg/mL). The lowest vitamin D concentration was discovered among the age 19-44 group. The main reason is possibly due to the lack of the correct knowledge regarding vitamin D.

The role of vitamin D in pregnancy is even more important, because the vitamin D level in mom-to-be would affect the vitamin D content of the fetus. Many studies have confirmed that vitamin D has different effects on women who are trying to conceive, in pregnancy and lactation. In 2009, an Australian study indicated that mothers with vitamin D deficiency had an average birth weight reduction of 200 grams in their neonates. Researches in the Netherlands also revealed that insufficient prenatal levels of vitamin D increases the risk of fetal underweight by 2.4 times. The importance of vitamin D in maternal and child health has been confirmed by more and more clinical studies.

In addition, studies have found that the weight of pregnant women is very likely linked to the vitamin D deficiency. In another word, pregnancy overweight is related to low vitamin D content in the body. Compared with lean pregnant women (BMI < 25) – 36% of them lack of vitamin D, 61% of obese mothers (BMI > 30) suffer from a severe deficiency of prenatal levels of vitamin D.

How much vitamin D should a pregnant woman take? It's generally recommended to take at least 400 to 600 IU of vitamin D3 daily. American Association of Clinical Endocrinology suggests to take 1500-2000 IU daily. If the pregnant woman is severely deficient, a higher dose should be supplemented under medical supervision. As for what is the safe dose range? A clinical study published in the journal “J Bone Miner Res” in 2011 indicated that a daily supplement of 4000 IU units of vitamin D3 is safe for pregnant women without side effects and can effectively increase vitamin D content in the body. The results from many other clinical trials also suggested that 2000-4000 IU per day for pregnant women is safe (Hollis BW, 2011; Hollis BW, 2013; Dawodu A, 2013; Grant CC, 2014). As for the Tolerable Upper Intake Level, the US National Institutes of Medicine (IOM) recommends an upper limit of 4000 IU per day.