Science and Medicine

“Low prices, convenience, and free toys target the middle class—especially budget-conscious, hurried parents—very well," Leigh said.

As earnings increase from low to middle class, so does the frequency of fast-food dining, weakening the argument that fast food can be blamed for higher rates of obesity among the poor.

“There is a correlation between obesity and lower income, but it cannot be solely attributed to restaurant choice,” says J. Paul Leigh, professor of public health sciences at University of California, Davis. “Fast-food dining is most popular among the middle class, who are less likely to be obese.”

For a new study, published online in Population Health Management, Leigh and co-author DaeHwan Kim used data from the 1994 to 1996 Continuing Survey of Food Intakes by Individuals and the accompanying Diet and Health Knowledge Survey.

The nationally representative sample of nearly 5,000 people in the U.S. included data about food consumption patterns, including restaurant visits over two nonconsecutive days, which was compared with demographic variables such as household income, race, gender, age and education.

Read more: Middle Class, Not Poor, Eat More Fast Food

Diagram shows relationship between DNA repair rates, time of day and skin cancer risk. Credit: (Credit: Laura A. Lindsey-Boltz, PhD, Sancar lab)

Research from the University of North Carolina at Chapel Hill suggests that the timing of exposure to UV rays—early in the morning or later in the afternoon—can influence the onset of skin cancer.

The study, performed in mice, found that exposure to UV radiation in the morning increased the risk of skin cancer by 500 percent over identical doses in the afternoon. Although mice and humans both reside on a 24-hour day, the "circadian" clocks of these nocturnal and diurnal creatures run counter each other. This key difference in biology means that humans are most protected from the sun's harmful rays when mice are most susceptible, and vice versa.

"Therefore, our research would suggest that restricting sunbathing or visits to the tanning booth to morning hours would reduce the risk of skin cancer in humans," said senior study author Aziz Sancar, MD, PhD, a member of the UNC Lineberger Comprehensive Cancer Center and Sarah Graham Kenan professor of biochemistry and biophysics in the UNC School of Medicine. Sancar is also a member of the National Academy of Sciences and the Turkish Academy of Sciences "However, further studies in humans are needed before we can make any definitive recommendations."

Sancar has previously shown that a protein called XPA, responsible for repairing the DNA damage wrought by UV radiation, waxes and wanes throughout the day. In a study published online the week of October 24-30 in the Proceedings of the National Academy of Sciences, he and his colleagues looked to see if the cyclical nature of this DNA repair molecule had an influence on the onset of skin cancer.

Read more: Morning UV Exposure May Be Less Damaging to the Skin