Written by Greg Arnold, DC, CSCS. Women in the group with lower blood levels of vitamin D had double the risk of a C-section delivery.

The Mayo Clinic defines cesarean section birth as “a surgical procedure used to deliver your baby through an incision in your abdomen” (1). Although a cesarean birth can be necessary to save the life of both mother and infant, the World Health Organization states that “no region in the world is justified in having a cesarean rate greater than 10 to 15 percent.” Yet the rate of c-section deliveries in the US has more than quintupled from 5% in 1970 to 23.8% in 1989 (2) and is now at 30.2% (3)

967,000 cesareans were performed in the US in 1989 and the Public Health Citizen’s Research Group estimates that more than half the cesareans performed in 1987 were unnecessary and resulted in 25,00 serious infections, 1.1 million extra hospital days and a cost of over $1 billion (4). About 500 women a year die from bleeding, infections and other complications of cesarean sections, although these may be related to the reasons the operation was performed and not just to the procedure itself (1).

Now a new study (5) has found that vitamin D blood levels may be related to the rate of c-section births. In the study, researchers drew blood samples on more than 250 women after childbirth to measure for vitamin D levels. They defined vitamin D deficiency being below 15 nanograms per milliliter (< 37.5 nanomoles per liter) as defined by the Centers for Disease Control (6) although other research has found vitamin D levels even below 50 nanomles/liter to be indicative of vitamin D deficiency (7).

The researchers found that women with vitamin D levels less than 37.5 nmol/L had double the rate of c-sections than women with vitamin D levels greater than 37.5 nmol/L (28% vs. 14%). What’s more, women who had c-section births had vitamin D levels 27% lower than women who delivered vaginally (45.0 nmol/L vs 62.5 nmol/L).

As a possible explanation for why vitamin D deficiency was related to c-section rates, researchers cited vitamin D’s role in helping with calcium absorption and that “a slight lowering of calcium is related to both skeletal muscle and smooth muscle strength and may play a role in initiation of early labor.” For the researchers, “Vitamin D deficiency was associated with increased odds of primary cesarean section.”

Source: Merewood, Anne, Supriya D. Mehta, Tai C. Chen, Howard Bauchner, and Michael F. Holick. “Association between vitamin D deficiency and primary cesarean section.” The Journal of Clinical Endocrinology & Metabolism 94, no. 3 (2009): 940-945.

© 2009 by The Endocrine Society

Posted January 16, 2009.


  1. “C-section” posted on the Mayo Clinic website.
  2. “Cesarean Birth Fact Sheet” posted on Childbirth.org.
  3. Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data for 2005. Natl Vital 40 Stat Rep 2006;55(11):1-18.
  4. “Public Citizen Study” posted on Childbirth.org.
  5. Merewood. A.  Association Between Vitamin D Deficiency and Primary Cesarean Section. J Clin Endocrin Metab. First published ahead of print December 23, 2008 as doi:10.1210/jc.2008-1217.
  6. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine. Dietary reference intakes for calcium, phosphorus, magnesium, vitamin D, and fluoride: National Academy of Sciences,1997.
  7. Holick MF. Vitamin D deficiency. N Engl J Med 2007;357(3):266-81.