Effect of Vitamin D Supplementation on Endothelial Function in Obese Adolescents

Effect of Vitamin D Supplementation on Endothelial Function in Obese Adolescents

Vitamin D deficiency has been linked to endothelial dysfunction in adults. Obese adolescents have a high prevalence of Vitamin D deficiency as well as evidence of endothelial dysfunction. Our hypothesis is that supplementation of Vitamin D deficient adolescents with Vitamin D would lead to improvement in endothelial dysfunction.

Subjects had a brief screening visit with one of the study team members. Past medical history, current medications and a brief dietary history was taken. The dietary history was taken to assess calcium intake in a day and was obtained via the validated Short Calcium questionnaire. Blood pressure, heart rate as well as height,weight, waist and hip circumference measurement was obtained by study staff. In addition, a brief physical examination to determine Tanner stage was also completed. This involved examination of both breasts and genitalia for adolescent female and only genitalia in males. A physical activity questionnaire (IPAQ) was also administered by the study staff at this visit. A blood draw of 5 ml to measure plasma 25(OH) D, calcium, phosphorus was obtained as part of the screening visit. For girls who had started menstruating, a urine pregnancy test was also obtained.

After the screening visit eligible subjects had baseline biochemical tests and an endothelial function assessment. Study participants received a pill container with six total pills of vitamin cholecalciferol (D3) (1 pill = 50,000 IU), with directions to take two pills once a month (100,000 IU) at the same time for a period of 3 months. Compliance was assessed at the 3 month visit by counting the number of pills remaining in the container.

At 1 month, the subjects had tests for serum calcium and 25 hydroxy vitamin D levels. A urine test for random calcium to creatinine ratio was also obtained.

At 2 months, the serum calcium, 25 hydroxy vitamin D levels, and calcium to creatinine ratio tests were repeated.

At the end of 3 months, biochemical tests and an endothelial function assessment were repeated. Medical history, questionnaires, and the physical exam were also repeated.

Inclusion Criteria:

1. Age 12-18 years
2. BMI >95% for age and gender
3. 25 (OH) D levels less than 30 ng/ml

Exclusion Criteria:

1. 25 (OH) D levels >30 ng/mL
2. Serum calcium >10.4 mg/dL
3. Serum phosphorus > 4.7 mg/dl
4. Pregnancy or nursing
5. Current cancer
6. Patients on vitamin D3 supplementation exceeding 400 IU/day
7. Hypertension defined as Blood Pressure over the 95th percentile for age, gender and height
8. Dietary calcium intake exceeding 1500 mg/day
9. Hepatic or renal disorders
10. Type 1 or type 2 diabetes mellitus
11. Subjects receiving insulin, metformin, or oral hypoglycemic medications
12. Subjects with malabsorption disorders (celiac disease, cystic fibrosis, inflammatory bowel disease)