Vitamin D during Pregnancy and Breastfeeding – Part 1

Ann Creighton-Zollar, Professor Emerita, Virginia Commonwealth University

The sun is the ultimate source of all energy that sustains human life.

Vitamin D is synthesized when ultraviolet B (UVB) rays from the sun interact with a form of cholesterol found in human skin. Technically, the substance that we call vitamin D is not an “organic micronutrient.” It is a prohormone, a precursor to a hormone. It has long been understood that a severe deficiency in vitamin D produces rickets, a devastating and sometimes deadly condition involving major skeletal deformities. In our bodies vitamin D is transformed into a powerful hormone with effects on metabolism and immune function that go well beyond bone. Maternal vitamin D status during pregnancy has an impact on the health of the mother, on birth outcomes, and on both the immediate and long term health of the child.

Maternal vitamin D status continues to be urgently important to the health of the nursing infant. When maternal vitamin D status is sufficient, vitamin D transfer via breast milk is adequate to meet infant needs. When the mother’s vitamin D level is less than sufficient her breast milk will not contain enough vitamin D to meet the needs of the infant. Unfortunately, insufficient/deficient vitamin D status is highly prevalent among pregnant and lactating women in the US because not enough UVB reaches their skin. A group of researchers working in South Carolina have found that when pregnant women are provided with 4000 IU (International Units) of supplemental vitamin D per day they are able to produce breast milk which meets the needs of their infants. They have also found that 6400 IU/d have the same effect on the breast milk of lactating women. However, vitamin D supplementation at these levels is considered to “high dose,” potentially toxic and they are very controversial in medical circles.

In order to understand why vitamin D levels among many pregnant and lactating women tend to be less than sufficient, it is necessary to understand some of the many factors which prevent enough UVB from reaching their skin. Before it can reach a woman’s skin, UVB emitted by the sun must first reach the surface of the earth. The

amount of UVB reaching the surface of the earth is influenced by factors like air pollution, cloud cover, and altitude. Air pollution can either absorb UVB or reflect it back into space. The water droplets in cloud cover scatter some of the UVB rays back into space. At higher altitudes less of the UVB rays are filtered out than are filtered out closer to sea level. Perhaps the easiest way to determine the altitude of the city in which you live is to Google “altitude of [your town].”

The most well-known factor in determining how much UVB reaches the skin is the angle of the sun’s rays as determined by the time of day, the season of the year, and latitude. When the rays from the sun enter the atmosphere on too much of an angle (more acutely), the UVB portion of them is diffused or blocked. This happens in the early morning and in the later part of the day. It happens during the period of the year when no vitamin D production is possible. This “vitamin D winter” often overlaps with but is not identical to the season of winter. The length of this period increases as you move farther from the equator in either direction.

At latitude 37°33’N, Richmond, Virginia has a vitamin D winter that is estimated to last from November through early March. This means that no one is able to synthesize vitamin D from sunlight in the Richmond area during this time period, no matter how brightly the sun shines. The season simulator on the website of the University of Nebraska-Lincoln provides an interactive visual approach to understanding how the angle of the rays from the sun changes with season and latitude (https://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.html). The simulator makes it very easy to see that during its “vitamin D winter” the light from the sun is striking latitude 37°33’ N at an angle that is much too acute for UVB to get through to the skin of any metro Richmond residents. To find the latitude of other cities in the US, click here.

Season of the year, time of day, and latitude also play a role in determining how much time a person must spend in the sun in order to synthesize vitamin D effectively. An important characteristic of human beings which determines how long they must be exposed to UVB in order to synthesize vitamin D is how much melanin their skin contains, or skin color. While a person with very fair skin type can make as many as 10,000 IU of vitamin D in 15 minutes (when the season, latitude, and time of day make UVB available). It could take a person with a much darker skin type as much as six times longer under the same circumstances. Many people seriously underestimate how much skin they need to expose and how much time they need to spend in the sun in order to synthesize a sufficient amount of vitamin D.

Table 1 Skin Types and Sun Exposure

There are of course, other factors which influence the amount of vitamin D produced through UVB exposure. These include being behind glass, the amount of skin exposed, and wearing sunscreen. UVB does not penetrate window glass. Very little vitamin D is synthesized when only the face and hands are exposed. Sunscreen with an SPF as low as eight blocks 95 percent of the UVB rays to which the wearer is exposed.

The best estimates that I have of the vitamin D status of pregnant women in the Richmond area are data from research carried out in South Carolina. National data are not available. Scientists have not yet reached a consensus on what numbers should be used as cutoff points for different categories of vitamin D status. The Institute of Medicine (IOM) in its controversial 2011 report defined a circulating 25(OH)D of 20 ng/mL as generally adequate for 97.5% of the population and a level under 12 ng/mL as deficient for bone health. The researchers in South Carolina define 32 ng/mL of circulating 25(OH)D as sufficient; levels between 20-32 ng/mL as insufficient; and any level below 20 as deficient. (Because of these differences it is impossible to understand what a physician means when vitamin D levels are described as “fine” or “normal.” It is strongly recommended that the results of vitamin D screenings be requested in ng/mL). Since Richmond is at higher latitude than the city in which these data were collected, there is no easily apparent reason to expect that pregnant women in Richmond will have levels of vitamin D that are significantly higher.

Table 1: Prevalence of vitamin D deficiency (%) according to race/ethnicity among diverse pregnant women in sun rich South Carolina

Overall, 48% of the participants in this study were vitamin D deficient, with an additional 37.1% insufficient. As shown in Table 1, this varied significantly by self-identified race. The greatest degrees of deficiency and insufficiency were seen in the African-American women, with 68.3% clearly having deficiency (concentration <20 ng/mL) and 94.3% having either deficiency or insufficiency (concentration <32 ng/mL). What might be surprising, however, is that in the sun rich environment of South Carolina, 70% of the women who self-identified as Caucasian were vitamin D insufficient. The Hispanic study participants had rates of insufficiency and deficiency that were between those of Caucasians and African Americans. When these data are considered in terms of breast milk, only 15% of the participants had vitamin D levels

high enough to assume that they could produce breast milk with a vitamin D concentration high enough to meet the needs of their infants.

The only way for a woman of any race or ethnicity living anywhere in the world to know her vitamin D level is to have the test. What options are open to women who want to breastfeed and find that their vitamin D levels are insufficient to meet the needs of their infants? The American Academy of Pediatrics (AAP) recommends supplementation for the infant. Nationally important breastfeeding advocates appear to say nothing. While the researchers in South Carolina say that it is safe and effective for mothers to be supplemented at levels much higher than conventional recommendations.

In 2008, the American Academy of Pediatrics (AAP) issued practice guidelines

that called for 400 IU/d of vitamin D for all infants, children, and adolescents, about the amount of vitamin D in a teaspoon of cod liver oil, starting in the first few days of life. Since commercially produced formulas are fortified with vitamin D, the guidelines specified that all infants who consume < 1L of fortified formula per day, including exclusively breastfed infants should receive supplemental vitamin D.

The recommendation that exclusively breastfed infants receive vitamin D supplementation has yet to be fully implemented in the US. Many pediatricians do not provide vitamin D counseling that is consistent with the AAP guidelines. And some very important breastfeeding advocates seem to have chosen simply to ignore vitamin D. The United States Breastfeeding Committee (USBC) publishes core competencies in breastfeeding care and services for health professionals that include no mention of vitamin D. In 2011 the Surgeon General of the United States announced, with no mention of vitamin D, an initiative to support breastfeeding (https://www.surgeongeneral.gov/library/calls/breastfeeding/index.html). Even a newly released (April 15,

2013) campaign designed for African American women, It’s Only Natural, makes no mention of vitamin D.

Dr. Bruce Hollis, Dr. Carol Wagner, and their colleagues, who are conducting ground breaking research in South Carolina, say that mothers themselves can be safely and effectively supplemented in order to produce breast milk that meets the vitamin D needs of their infants. Using a random controlled trial (RCT) design, which is considered to be the ideal model for biomedical research, this group of researchers has demonstrated that when pregnant women are provided with 4000 IU/day supplemental vitamin D they can safely and effectively produce breast milk that meets the need of infants. Dr. Bruce Hollis, one of the primary researchers provides a very interesting presentation on Vitamin D Needs during Pregnancy and Lactation. Another member of this research group, Dr. Carol Wagner was the lead author of a 2011 book, New Insights on Vitamin D during Pregnancy, Lactation, and Early Infancy. In this book the authors predicted that 6400 IU/d would be their recommendation for lactating women at the conclusion of their ongoing RCT. When the researchers present the results of their study which support 6400 IU/d for lactating women at the annual meeting of the Pediatric Academic Societies in May, 2013, the response will not be immediate changes in policy.

During the same year (2011) that this group of researchers presented their findings on vitamin D supplementation during pregnancy and published their book of new insights, the American College of Obstetricians and Gynecologists (ACOG) refused to recommend a rate of supplementation for pregnant women higher than the 400 IU/d found in most prenatal vitamins. The ACOG did say that 1000-2000 IU/d is generally considered safe, but that rate of supplementation will not move all insufficient/deficient mothers to a level that will meet the needs of their infants.

The very large gap between recent research findings and established professional guidelines reflect that we are living through the “Vitamin D Revolution.” This is not hyperbole. This is a scientific revolution that would be recognized by Thomas Kuhn. A new vitamin D paradigm is replacing an older paradigm through a process that involves the kind of conflict and struggle implied by the term “revolution.” It will be years before enough RCTs with large enough study populations have been carried out in enough places to produce changes in national policy and professional guidelines. In the meanwhile, if you are interested in optimal health for your family or your community, you will need enough information to make decisions. Some of the additional information that you must think about and discuss with your physician will be presented in Part 2 of this essay on vitamin D during pregnancy, lactation, and early infancy.

Ann Creighton-Zollar earned a BA (1973), MA (1976), and PhD (1980) in sociology from the University of Illinois Chicago. She joined the faculty of Virginia Commonwealth University’s Department of Sociology in 1981 (with a joint appointment

in African American Studies). Creighton-Zollar taught classes, provided service, and engaged in research and scholarship.

She is the author of several books, chapters in books, and a number of peer reviewed journal articles. She is a Certified Family Life Educator with a focus on improving the health outcomes of infants and children by improving the parenting capacity of parents and other caregivers. She has studies racial disparities birth outcomes. After retiring from the university in 2010, she decided to learn more about the role of nutrition in health and enrolled in the Master of Science in Health and Nutrition Education at Hawthorn University. Vitamin D Needs during Pregnancy, Lactation and Early Infancy is the topic of her thesis project.