Controlled clinical trials with vitamin D supplements have discovered lower levels of 25(OH)D in obese and overweight people, probably because vitamin D is distributed in a larger body volume or because of a slower release into the circulation of that stored in adipose tissue.
However, a meta-analysis quantifying the effects of vitamin D supplementation indicated that obesity indices did not improve significantly despite increased serum 25(OH)D levels.
The results of interventional studies evaluating the effect of vitamin D supplementation on excess weight (overweight/obesity) and serum lipid profile in relatively healthy people at an early age remain uncertain and inconsistent. Additionally, there are few intervention studies in the Latin American population, in which seasonal variation does not have such a marked effect on vitamin D levels.
Therefore, the present study was conducted with the objective of evaluating the efficacy of oral administration of vitamin D supplementation in reducing BMI and lipid profile in adolescents and young adults from a cohort in Bucaramanga, Colombia.
One of the strengths of the study was the quantification of the concentration of vitamin D in the blood, which made it possible to follow the intra-person variation in its metabolism. In addition, the analytical reliability of 25(OH)D in the quantification was monitored through DEQAS (the vitamin D External Quality Assessment Scheme), since the laboratory where the quantification was carried out could do it.
The authors, from Centro de Investigaciones, Fundación Cardiovascular de Colombia, conducted a triple-blind parallel two-arm randomised controlled clinical trial involving 101 young adults.
Participants were randomly assigned to one of two doses of vitamin D (1000 or 200 international units (IU), provided by Farma D) administered daily for 15 weeks. The primary outcomes were serum 25(OH)D levels, BMI and lipid profile. The secondary outcomes were waist-hip ratio, skinfolds and fasting blood glucose.
The researchers found a mean ± SD plasma concentration of 25-hydroxyvitamin D [25(OH)D] was 25⋅0 ± 7⋅0 ng/ml at baseline, and after 15 weeks, it increased to 31⋅0 ± 10⋅0 ng/ml in the participants who received a daily dose of 1000 IU, (P < 0⋅0001). For the participants in the control group (200 IU), it went from 26⋅0 ± 8⋅0 ng/ml to 29⋅0 ± 8⋅0 ng/ml (P = 0⋅002).
There were no differences between groups in body mass index. There was a statistically significant decrease in LDL-cholesterol between the intervention group v. the control group (mean difference −11⋅50 mg/dl (95 % CI −21⋅86 to −1⋅15; P = 0⋅030).
The conclusions of the present study were two different doses of vitamin D supplementation (200 IU v. 1000 IU) produced changes in serum 25(OH)D levels over 15 weeks of administration in healthy young adults. No significant changes were found in the body mass index when the effect of the treatments was compared. A significant reduction in LDL-cholesterol was found when comparing the two intervention groups.
The authors conclude: "No significant change in BMI was evident when the treatments were compared. However, a significant reduction in LDL-cholesterol was found when the two intervention groups were compared.
"Despite the lack of solid conclusions about the clinical benefits of vitamin D supplementation in published studies, achieving vitamin D sufficiency remains crucial in patients with cardiovascular and metabolic conditions."
Mechanisms of action
The authors explain the relationship between vitamin D and BMI is mainly due to the participation of vitamin D as a pre-hormone and its ability to go to many specific tissues in the body. Vitamin D is a fat-soluble compound that has been related to obesity due to its deficiency at the serum level in the body due to the sequestration of vitamin D in adipose tissue, which results in lower concentrations of circulating 25(OH)D.
The previous is consistent with the results of this pilot study, where no significant change in BMI was found when the treatments were compared. The level of evidence that has been found so far about vitamin D supplementation and excess weight is mainly given in groups that present a base deficiency of vitamin D in the blood, unlike the current study.
Various observational studies across the world indicate an association between vitamin D deficiency and low levels of high-density lipoproteins (HDL) and high triacylglycerols, as well as higher levels of apolipoprotein E(Reference Jorde and Grimnes34,Reference Skaaby, Husemoen and Pisinger35) . This is consistent with the current trial, as it showed a significant reduction in LDL-cholesterol and a positive effect on triacylglycerol levels in the intervention group.
However, for total cholesterol and HDL levels, favourable results were observed for both the group that received 1000 and 200 IU of vitamin D. The dose of vitamin D supplementation has been reported to explain part of the variations between the results in different populations. Therefore, observing the impact of different doses within the same population elucidates more specific results and contributes to its better understanding.
Regarding limitations, the research did not include a placebo group for ethical reasons. A smaller vitamin D dose of 200 IU/d was included to provide an adequate dose-response comparison with the higher dose. Another limitation is that being a pilot study the sample size was not optimal, and there was no evidence of significance in our findings on total cholesterol, HDL-cholesterol and triacylglycerols.
Source: Journal of Nutritional Science
"Efficacy of vitamin D supplementation in reducing body mass index and lipid profile in healthy young adults in Colombia: a pilot randomised controlled clinical trial"
Serrano, N., et al