For Obese Teens, This Supplement May Not Help

Vitamin D supplements in obese teens had few benefits and some risks

Some obese teens turn to dietary supplements to try to improve their health. In the case of vitamin D, that might not necessarily be a good thing.

Researchers from the Mayo Clinic Children’s Center studied the effects of vitamin D supplements in obese teens, who are often vitamin D deficient. They found that although the teens’ vitamin D levels reached normal, health indicators like weight, blood pressure and blood flow did not improve.

"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 study leader Seema Kumar, MD, a pediatric endocrinologist at the Mayo Clinic Children's Center, in a press release. "We're not saying the links between vitamin D deficiency and chronic diseases don't exist for children — we just haven't found any yet."

Research has shown vitamin D deficiency may be linked to weight-related complications like heart disease. Caregivers and clinicians sometimes start teens on vitamin D supplements in an effort to counteract these complications.

In this study, Dr. Kumar, who has studied the effects of vitamin D supplements in children for a decade, and colleagues looked at how vitamin D supplements affected the lining of the blood vessels.

The function of this lining, or endothelium, gives an indication of early heart disease. Vitamin D supplements have been shown to improve endothelial function.

No one had studied this effect in obese teens, however. The 19 study patients had low vitamin D levels and were obese.

These patients received a once-a-month dose of oral vitamin D, which had been shown to be effective in raising vitamin D levels.

After three months, vitamin D levels increased to normal in 15 of the 19 teens, Dr. Kumar and team found. Endothelial function, however, did not improve.

The teens in this study did not lose weight, and serum cholesterol and triglycerides increased. High cholesterol and triglycerides can increase the risk of heart disease.

"I have been surprised that we haven't found more health benefit," Dr. Kumar said. "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."

Dr. Kumar also noted that taking too much vitamin D can cause kidney problems and gastrointestinal side effects.

This study was published Aug. 14 in the journal Pediatric Obesity.

The National Center for Advancing Translational Sciences funded this research. Dr. Kumar and team disclosed no conflicts of interest.