Criticizing Vitamin D Level in Pregnant Women After Gastric Bypass

Excerpt

I read with interest the paper entitled as “Non-pregnant Women Have a Lower Vitamin D than Pregnant Women after Gastric Bypass”, by Cruz et.al. [1]. When we compare pregnant with non-pregnant women after gastric bypass, we should consider some issues. Are these two different populations really comparable? Do they have similar baseline characteristics, specifically vitamin D and its related hormones affecting vitamin D level? Should the confounders like supplementation intake be adjusted or the compliance of use be considered? It seems the answer to all of the above questions is yes. Neglecting the timeline of the events or natural history of each disease would eventually result in reverse causation. The causal pathway is also important. Does pregnancy really cause higher vitamin D level? It is very unlikely. The role of important factors predispose pregnant women to have higher level of vitamin D must be considered. If the level of other minerals and vitamins is compared between pregnant and non-pregnant women, the results will be the same most of the time, and such comparison will not help to solve an important question. Despite, following pregnant women in different situations (before, during, and after pregnancy in each case) would elucidate either pregnancy or supplementation is important for such change in vitamin D level. Moreover, knowing supplementation prescription and adherence will help adjust the analyses for the confounders and assess their role in vitamin D level to answer either supplementation or pregnancy itself has effects on vitamin D level. There are some cases with and without supplementary minerals and vitamins and also different adherence to proposed supplementation. …