Pregnant women who develop high blood pressure tend to have lower levels of vitamin D.
The condition is known as early-onset severe pre-eclampsia, and while it arises in about 2 to 3% of pregnancies, it contributes to about 15% of preterm births
in the U.S. each year alone.
Pre-eclampsia is a syndrome marked by a sudden increase in blood pressure and a build up of protein in the urine due to stress on the kidneys. Early-onset severe pre-eclampsia is a particularly serious form that arises before the 34th week of pregnancy.
In the current study, researchers found that vitamin D levels were generally lower among 50 women with early severe pre-eclampsia
compared with those of 100 healthy pregnant women. The average vitamin D level in the former group was 18 nanograms per millilitre (ng/mL), versus 32 ng/mL in the latter group.
There is debate over what constitutes an adequate level of vitamin D in the blood. But many experts say that at least 32 ng/mL is needed for overall health.
A few past studies have found an association between vitamin D
and pre-eclampsia in general. Now more work is needed to see whether pregnant women's vitamin D levels predict the odds of pre-eclampsia developing - and whether raising those levels with vitamin D supplements lowers women's risk of the complication, according to Dr. Christopher J. Robinson, of the Medical University of South Carolina in Charleston.
The current findings are based on 50 pregnant women with early-onset pre-eclampsia seen at the Medical University of South Carolina, along with 100 women with healthy pregnancies.
Of the pre-eclampsia group, 54% were deemed to have vitamin D deficiency (less than 20 ng/mL), versus 27% of the healthy group. Only 24% of women with pre-eclampsia had vitamin D levels greater than 32 ng/mL, compared with 47% of their healthy counterparts.
When Robinson and his colleagues accounted for a number of factors in pre-eclampsia risk - including older age, heavier body weight and African American race - vitamin D levels were independently related to the odds of early pre-eclampsia.
A 10 ng/mL increase in vitamin D was linked to a 63% reduction in the odds of the complication.
It is biologically plausible, Robinson said, that the vitamin could affect pre-eclampsia risk. Vitamin D acts as a hormone, and lab research has found that it may affect the regulation and function of proteins in the placenta; problems in the development of the placenta are believed to be at the roots of pre-eclampsia.How much vitamin D do you take?