Low Vitamin-D Levels in Adolescents Predict CVD Risk Factors

Marlene Busko

March 19, 2009

From Heartwire — a professional news service of WebMD

March 19, 2009 (Palm Harbor, Florida) — In a large study of adolescents, low serum levels of 25-dihydroxyvitamin D (25[OH]D) strongly predicted prevalence of hypertension, hyperglycemia, and metabolic syndrome [1]. The findings were reported at the AHA 49th Annual Conference on Cardiovascular Disease Epidemiology and Prevention.

Adolescents with vitamin-D levels in the lowest quartile were almost four times more likely to have metabolic syndrome than those with vitamin-D levels in the highest quartile. "I think that is quite alarming," lead author Dr Jared P Reis (Johns Hopkins Medical Institutions, Baltimore, MD) said in an AHA podcast issued to the media.

However, it is too early to recommend vitamin-D supplementation, he added. "Additional studies are probably necessary--especially large sets of clinical trials--to determine whether or not vitamin-D supplementation is actually associated with a reduced risk of developing CVD risk factors, especially among adolescents."

Increasing evidence suggests that vitamin-D deficiency in adults may increase the risk for hypertension, diabetes, and CVD, but little is known about the link between vitamin-D levels and CVD risk factors in adolescents.

To investigate this relationship, the researchers analyzed data from 3577 adolescents 12 to 19 years old (51% boys) who participated in the 2001–2004 National Health and Nutrition Examination Survey (NHANES 2001–2004).

The adolescents had a mean serum 25(OH)D level of 24.8 ng/mL; those with vitamin-D levels in the lowest quartile (<15 ng/mL) were much more likely to have metabolic syndrome, hyperglycemia, or hypertension than those with vitamin-D levels in the highest quartile (>26 ng/mL).

Odds of CVD Risk Factors, Lowest vs Highest Vitamin-D Quartile

Risk factor Odds ratio (95% CI)*
Hypertension 2.36 (1.33–4.19)
Hyperglycemia 2.54 (1.01–6.40)
Metabolic syndrome 3.99 (1.21–13.20)

*Adjusted for age, sex, race/ethnicity, body-mass index, socioeconomic status, and physical activity

Mean vitamin-D levels were lowest in African Americans (15.5 ng/mL), intermediate in Mexican Americans (21.5 ng/mL), and highest in whites (28.0 ng/mL). "This is thought to be due to the fact that African Americans have much more melanin in their skin, and this blocks UVB light and blocks the ability to produce vitamin D in the skin, so African Americans are at much higher risk of being vitamin-D deficient," said Reis.

Low vitamin-D levels were also strongly associated with being overweight and having abdominal obesity (p for trend <0.001 for both). This is likely because vitamin D is taken up within fat tissue, not because low vitamin-D levels lead to obesity, according to Reis.

Raises Important Questions

The study confirms that low vitamin D is linked with CVD risk factors in adolescents as well as adults, Dr Robert H Eckel ((University of Colorado, Denver, AHA past president), who was not involved in the study, told heartwire .

"I think there are more questions than answers, but I think this is an important finding, and an important trend that needs to have a more drilled-down, scientific approach to understand mechanisms," he said.

Further research is needed to determine whether low levels of vitamin D in adolescents are due to poor diet, lack of sunlight, both factors, or even to an increase in obesity, and whether they predict adverse health events in 20 to 30 years, he added.

Vitamin-D Deficiency Increasing

According to other research presented at the meeting, prevalence of vitamin-D deficiency in adults and adolescents in the US has risen sharply over the past 20 years [2].

Dr Sandy Saintonge (New York Hospital Queens, NY) and colleagues analyzed NHANES data and reported that prevalence of vitamin-D deficiency--defined conservatively as serum 25(OH)D below 11 ng/mL--rose from 2.6% in 1988–1994 to 9.2% in 2005–2006.

This is an "impressive" increase over a short interval, said Eckel.

Prevalence of vitamin-D deficiency during 2001–2006 was 28% to 40% if a less conservative cutoff of 20 ng/mL was used and was 70% to 80% if a cutoff of 30 ng/mL was used.

Further study is needed to determine optimal vitamin-D levels, according to the researchers. While the American Academy of Pediatrics now recommends a daily intake of 400 IU vitamin D--which can come from consuming milk, oily fish, or fortified foods or spending 10 to 15 minutes in the sun--other experts suggest that at least 1000 IU per day are needed.

The authors disclosed having no conflicts of interest.

  1. Reis JP, von Muhlen D, Miller III ER, et al. Vitamin D status and cardiovascular disease risk factors in the us adolescent population. AHA 49th Annual Conference on Cardiovascular Disease Epidemiology and Prevention; March 11, 2009; Palm Harbor, FL. Poster P54.

  2. Saintonge S, Bang H, Vogiatzi MG, et al. Is the relevance of vitamin D deficiency increasing? Data from the National Health and Nutrition Examination Survey: 1988-1994 and 2001-2006. AHA 49th Annual Conference on Cardiovascular Disease Epidemiology and Prevention; March 11, 2009; Palm Harbor, FL. Abstract 9.

The complete contents of Heartwire , a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.

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