MITCHEL L. ZOLER
Low serum levels of vitamin D were linked to increased blood pressure, hyperglycemia, and obesity in an analysis of more than 3,500 American teenagers, a link previously seen in adults.
“Vitamin D plays a useful role in general human health. We are just now beginning to understand the role that vitamin D may play in cardiovascular health,” said Dr. Jared P. Reis, who presented a poster on the associations of vitamin D levels and cardiovascular risk factors at a conference on cardiovascular disease epidemiology and prevention sponsored by the American Heart Association.

His study analyzed data collected from 3,528 adolescents aged 12-19 during 2001-2004 in the National Health and Nutrition Examination Survey (NHANES), run by the National Center for Health Statistics. Their average age was 15, and 52% were boys.

The average serum vitamin D level for all participants was about 25 ng/mL, but a quarter had a level less 15 ng/mL, while another quarter had a level greater than 26 ng/mL.

The teens in the quartile with the lowest vitamin D level had an 11% prevalence of hypertension, 2.3-fold more common than those with the highest vitamin D levels. A fasting serum glucose level of 100 mg/dL or greater (impaired fasting glucose) occurred in 6% of those with the lowest vitamin D levels, 2.5-fold more often than those with the highest levels. And the average body mass index (BMI) in the low-vitamin quartile was about 31 kg/m2. Adolescents in this subgroup were greater than fivefold more likely to have a BMI at the 95th percentile or higher, compared with teens in the highest vitamin D quartile. All of the differences between the lowest and highest vitamin D quartiles were statistically significant, reported Dr. Reis, a researcher in the School of Public Health at Johns Hopkins University, Baltimore.

Those in the lowest vitamin D quartile also had a significantly higher rate of low levels of HDL cholesterol, high triglycerides, and metabolic syndrome, compared with the teens in the highest vitamin D quartile.

Vitamin D reduces activation of the renin-angiotensin system, thereby lowering blood pressure. It also reduces insulin release from pancreatic beta cells and raises insulin sensitivity. Low vitamin D levels produce opposite effects, activating renin-angiotensin to raise blood pressure, boosting insulin release, and lowering insulin sensitivity, he said.
Low vitamin D levels in blood are usually caused by lack of adequate sun exposure and poor diet. Another factor is obesity. Vitamin D is fat soluble, which means it tends to leave the blood and accumulate in fat, a process enhanced in obese people, Dr. Reis said.

Low dietary levels of vitamin D were linked to elevated percent body fat and visceral adipose tissue among teens in a separate talk given at the meeting. The study included 659 healthy teenagers, aged 14-19 years, who resided in or near Augusta, Ga. Their average age was 16, half were girls, and nearly half were African American. Vitamin D intake was calculated based on several 24-hour diet recall surveys for each participant.