A new analysis of data from a clinical trial suggests that the amount of free vitamin D in a pregnant woman's blood may be more important for her child's respiratory health than total vitamin D levels. The study focused on mothers with and without asthma and their children.
Researchers looked at blood samples from 518 pregnant women in the Vitamin D Antenatal Asthma Reduction Trial. They measured total vitamin D, vitamin D-binding protein, and estimated free vitamin D. They then tracked whether the children developed asthma or recurrent wheeze by age 3.
Among mothers with asthma, higher estimated free vitamin D levels were linked to a lower risk of asthma or wheeze in their children. This link was stronger than for total vitamin D or vitamin D-binding protein alone. For mothers without asthma, the relationship was different and less clear.
This is a post hoc analysis, meaning it was done after the main trial ended, so the findings are not definitive. The results suggest that free vitamin D might be a better measure of vitamin D status during pregnancy, but more research is needed before changing any recommendations.