Vitamin D: Is all the hype justified?
Recently there has been a significant increase in healthcare concerns about Vit D. Research suggests that these concerns may be justified. So what is it Vitamin D and should a person care?
VITAMINS: WHAT DO WE REALLY NEED TO KNOW?
Vitamin D is not really a vitamin based upon the definition of vitamin. A vitamin is a substance that the body needs in very small amounts but cannot produce. Vitamins are therefore essential micronutrients that must be derived from the diet. Vitamin D can be synthesized in the body and thus is more properly viewed as a hormone. Classically, Vit D has been associated with the intestinal absorption of calcium, magnesium, and phosphate. But Vit D has been implicated in a number of biological processes including some related to reproduction. Vit D can be derived from the diet in the form of ergocalciferol or can be synthesized in the skin, under the influence of sun light where cholesterol is converted to cholecalciferol. These compounds are metabolized in the liver and kidneys to the circulating form of Vit D (25- hydroxyvitamin D) and eventually to the active form of Vit D (1,25 hydroxyvitamin D). Many other tissues can metabolize Vit D to the active forms. The form of Vit D that is actually measured clinically is the 25- hydroxyvitamin D. Low vitamin D levels have been associated with disorders other than skeletal problems and include metabolic disease, immune disease, cancer, and skin diseases. While it may seem reasonable, supplementation with Vitamin D has not consistently been associated with improvement in the clinical disease.
VITAMIN D AND BABYMAKING
Vitamin D deficiency has been implicated in a number of reproductive processes and there are a large number of publications concerning Vitamin D. Therefore in order to make sense out of this, two systematic reviews and meta- analysis and one well-constructed stratified randomized control trial are used for the following discussion. A study by Rostami et al (2018) assessed the success of a screening program to identify pregnant women with low Vit D levels. There were two sites of care and the screening program was instituted at one site, while the other served as a control. For the group from the non-screening center, only 2% had Vit D levels above the minimum value. The group of women from the screening center identified as Vit D deficient were treated with Vit D. At the end of the study 53% of the women at the screening center had adequate Vit D levels and the adverse pregnancy outcomes of preeclampsia, gestational diabetes and preterm delivery were reduced by 60%, 50%, and 40% respectively. The studies demonstrated that a screening program can identify those women with low Vit D levels and treatment for these women can reduce adverse pregnancy outcomes.
An earlier meta-analysis from LV et al (2016) commented that there were relatively few articles concerning Vit D levels and pregnancy outcome in IVF. There were no randomized controlled trials and the authors only found 6 articles out of 134 potentially relevant articles that actually met the inclusion criteria. The authors evaluated two rates, the clinical pregnancy rate and the live birth rate. This is a common problem when evaluating literature about IVF since frequently the results are given as a clinical pregnancy rate. A clinical pregnancy rate simply means that an intrauterine gestation was observed on Ultrasound. The real rate that matters is determined by whether or not the procedure resulted in the birth of a term, healthy baby. The meta-analysis determined that there was no correlation between Vit D levels and the clinical pregnancy rate but there was a significantly higher birth rate when the Vitamin D levels were > 20 ng/ml.
Finally, a meta-analysis published by CHU et al (2018) posed the question: “Is serum vitamin D associated with live birth rates in women undergoing ART?” A search of the available literature by the authors identified 4615 citations of which 11 met the inclusion criteria for the study. While this may seem strange, it points out how much literature really is not relevant to many questions that pertain to the treatment of infertility and should serve as a caution for those trying to understand the vast amount of literature that can be accessed in today’s world of massive data. The study found a high prevalence of Vit D deficiency in that Vit D deficiency occurred in 34% of the populations studied. The meta-analysis demonstrated that women with normal Vitamin D levels had a higher live birth rate than those where the vitamin D was < 20 ng/ml. There was no attempt to stratify these results by age or diagnosis. The study calculated an odds ratio of 1.3. So if a person had a predicted chance for a pregnancy of 35% then having a low level of vitamin D would lower the chance of pregnancy to approximately 25%. The current state of the literature suggests that Vit D does play a role in the success of IVF. It will take a while before a definitive answer can be found so the decision about the measurement of Vit D levels in women undergoing IVF and the subsequent choice to treat low levels of vitamin D becomes a question about the danger of the treatment. Vitamin D treatment for women with low Vitamin D levels seems to be safe. Therefore, currently, measuring Vit D levels and treating if necessary seems to be the most prudent way to go.