Previous observational studies have suggested a possible link between vitamin D deficiency and a host of weight-related medical complications, including cardiovascular diseases and insulin resistance.
As a result, many now attempt to slow – or even reverse - some of the clinical complications associated with obesity through the use of high-dose vitamin D supplementation.
The new research, published in Pediatric Obesity, noted that obesity in children is particularly associated with vitamin D deficiency and endothelial dysfunction, which is an early marker of CVD in children and adolescents, and a risk factor for the development of diabetes. However, there is a lack of research to understand whether improving vitamin D levels via supplementation improves endothelial function in obese teenagers.
Led by Dr Seema Kumar from the Mayo Clinic Children's Center, the team performed an open-label prospective trial in a small group of obese teenagers with deficiencies in vitamin D status – with the aim of determining whether treatment with vitamin D3 improves endothelial function in the group.
"After three months of having vitamin D boosted into the normal range with supplements, these teenagers showed no changes in body weight, body mass index, waistline, blood pressure or blood flow," said Kumar.
Indeed the team noted that supplementation showed no benefits for risk factors of heart health or diabetes, and in some cases may have had the unintended consequence of increasing cholesterol and fat-storing triglycerides in some participants.
"I have been surprised that we haven't found more health benefit," added Kumar. "We're not saying it's bad to take vitamin D supplements at reasonable doses, and we know most obese teens are vitamin D deficient. We're just saying the jury is still out on how useful it is for improving overall health in adolescents."
Kumar and her colleagues recruited 19 obese adolescents aged between 13 and 18 years of age, with 25-hydroxy vitamin D (25[OH]D) levels <75 nmol L−1. Participants were supplemented with 100,000 IU vitamin D3 orally once per month for 3 months in an open-label, single-centre prospective trial.
The team assessed endothelial function by flow-mediated dilatation (FMD) of the brachial artery at study entry and one month after the third dose of vitamin D3. Blood tests covering biochemical markers including calcium, fasting lipids, glucose, insulin and high-sensitivity C-reactive protein, were also obtained, said the team.
“Our study demonstrated that once monthly treatment with 100 000 IU of vitamin D3 over a period of 3 months did not have an effect on endothelial function in obese adolescents, despite a post-treatment increase in 25(OH)D levels,” wrote the research team.
Kumar and her colleagues added that while their study demonstrates the short-term safety and efficacy of once monthly vitamin D3 treatment in obese adolescents, the lack of benefits to endothelial function were surprising.
In addition, the team noted that a further finding of an increase in total cholesterol following supplementation with vitamin D ‘are not particularly surprising’ and are consistent with those seen reported in adults.
They said that larger studies examining the impact of vitamin D treatment in adolescents with vitamin D deficiency and established endothelial dysfunction are now needed.
Source: Pediatric Obesity
Published online ahead of print, doi: 10.1111/ijpo.12059
“Effect of vitamin D3 treatment on endothelial function in obese adolescents”
Authors: A. Javed, et al