Field Notes

Vitamin D: More May Not Be Better

In recent years, healthy people have been bombarded by stories in the media and on health websites warning about the dangers of their vitamin D levels being too low and urging high doses of supplements to protect against everything from hypertension to hardening of the arteries to diabetes.

But new research from Johns Hopkins has found that blood levels of vitamin D higher than the top of the range suggested by the Institute of Medicine (IOM) confer no additional benefit. This finding, combined with results of a previous study by the same group noting potential harm from higher vitamin D levels in healthy people, has urged investigators to prescribe caution.

“Healthy people have been popping these pills, but they should not continue taking vitamin D supplements unchecked,” says study leader Muhammad Amer, MD, MHS, an assistant professor in the division of general internal medicine at the Johns Hopkins University School of Medicine. “At a certain point, more vitamin D no longer confers any survival benefit, so taking these expensive supplements is, at best, a waste of money.”

Amer stresses that there are some groups of people—the elderly, postmenopausal women, and people with kidney disease—who do benefit from higher blood levels of a vitamin vital to bone health. Such groups may need to take supplements.

In an article published online in The American Journal of Medicine, Amer and Rehan Qayyum, MD, MHS, also of Johns Hopkins, describe their review of data from more than 10,000 participants in the National Health and Nutrition Examination Survey (NHANES) from 2001 to 2004. They matched those data with mortality data from the National Death Index through December 2006.

When they looked at deaths from all causes, and cardiovascular disease specifically, those with blood levels of 21 ng/mL of 25-hydroxyvitamin D—the top of the range that the IOM considers adequate and at the low end of normal—cut their risk of death in one-half. Above 21 ng/mL, the data suggest that the protective effect appears to wane.

The primary source of vitamin D is the sun, and although it’s found naturally in few foods, commercially sold milk usually is fortified with it. Amer says as people spend more and more time indoors and slather their bodies with sunscreen when outdoors, concern is rising that many are vitamin D deficient. But he says there’s no set amount of supplementation that can bring someone up to 21 ng/mL because the way people process vitamins varies.

In research published in January 2012 in the American Journal of Cardiology, Amer and Qayyum found that increasing levels of vitamin D in the blood are linked with lower levels of a popular marker for cardiovascular inflammation: C-reactive protein. Beyond blood levels of 21 ng/mL, any additional increase in vitamin D was associated with an increase in C-reactive protein, a factor linked to stiffening of the blood vessels and an increased risk of cardiovascular problems. The team’s unpublished research also suggests a link between excess vitamin D and elevated homocysteine levels, another danger sign for cardiovascular disease.

Amer says people should consult with their physicians before starting vitamin D supplements and should have their blood levels checked. Still, he says, “Most healthy people are unlikely to find that supplementation prevents cardiovascular diseases or extends their lives,” and there’s no consensus among physicians on what’s the right level of vitamin D in the blood for healthy people.

“There are a lot of myths out there and not enough data,” he concludes.

— Source: Johns Hopkins Medicine

 

Fast-Food Near Schools Affects Blacks, Hispanics More Than Asians, Whites

When their schools are near fast-food restaurants, black and Hispanic adolescents are more likely to be overweight and receive less benefits from exercise than Asian or white students, according to a study published in the Journal of Public Policy & Marketing. The study underscores the importance of understanding how adolescents respond to fast-food availability near school.

“Our study demonstrates that fast-food near schools is an environmental influence that has magnified effects on some minority children at lower-income urban schools,” says Brennan Davis, PhD, an assistant professor of marketing at Baylor University who coauthored the study with Sonya Grier, PhD, an associate professor of marketing at American University in Washington, DC.

Students attending lower-income schools, on average, have a higher BMI and consume more soda. Likewise, urban schools have students who, on average, have higher BMIs and consume more soda. To put these results in perspective, the study found that for all students, having a fast-food restaurant 1 mile closer to school almost entirely cancels the body-weight benefits of exercising one day per week. However, for black and Hispanic students in lower-income urban neighborhoods, having a fast-food restaurant 1 mile closer to school may cancel the benefits of up to three days of exercise per week.

“The findings imply that it’s important to examine the behaviors and contexts associated with low-income and ethnic minority status in urban areas,” Grier says. “These populations not only are the fastest growing but also have the highest rates of obesity, and research is relatively limited.”

According to the study authors, the school environment is, more often than many other settings, one in which adolescents make food choices free from the family structure and parental control and can occur during lunch or before and after school. The study highlights the need to understand local targeted marketing strategies and outcomes according to income, ethnicity, and geographic segmentation. Many of the ethnic groups that are increasing in size and purchasing power and are increasingly of interest to marketers also are geographically concentrated.

“As mobile geodemographic location targeting increases, fast-food promotions will likely target those adolescents nearest to fast-food outlets and who are at greatest risk for obesity. Voluntary industry actions, or policies that support healthier food near schools, can contribute to healthier school food environments,” Davis says.

The current study builds on previous research, published in 2009 in the American Journal of Public Health, by Davis and Christopher Carpenter, PhD, an associate professor of economics and public policy at The Paul Merage School of Business at the University of California, Irvine, which found that students with fast-food restaurants within 1/2 mile of their school consumed fewer servings of fruits and vegetables, consumed more servings of soda, and were more likely to be overweight than were youths whose schools weren’t near fast-food restaurants.

In a yet-unpublished study, presented in 2009 at the Association for Consumer Research Conference Proceedings, Davis and Cornelia Pechmann, PhD, a professor of marketing at the Merage School, found that adolescents with higher social identification with people at school perceived restaurants near school to be socially closer, were more likely to have friends, and were more likely eat there more often. In contrast, students who were relatively low in social identification weren’t affected by the nearness of a fast-food restaurant. In other words, low social identifiers were relatively immune to nearby fast-food, while high social identifiers were highly vulnerable to it.

Student demographics and information on students’ body weight and height, which was used to determine BMI, came from their responses to the 2003-2005 California Healthy Kids Survey, an anonymous, school-based survey. More than 36% attended school in a large suburban area, and 55% attended school within a 1/2 mile of a fast-food restaurant. Respondents reported their age in years by category: 21% were age 12 and under, 11% were age 13, 24% were age 14, 12% were age 15, 23% were age 16, and 9% were age 17 or older. Slightly more than one-half of the students were female and 40% were white, 13% were Asian, 7% were black, 38% were Hispanic, and 18% were another ethnicity.

— Source: Baylor University