Why stress grays hair
Stress really does make hair go gray, at least in mice, Japanese scientists report in a paper that provides insights about aging and stem cells.
Ken Inomata and a team of researchers from Kanazawa University studied stem cells in hair follicles that give rise to new cells called melanocytes, which give hair its color. They watched the hair-growth cycle, comparing mice exposed to DNA-damaging radiation or chemicals to similar mice that were not exposed. The unexposed mice retained their normal hair color. But in the exposed mice, the melanocyte stem cells became mature melanocytes in a process called stem cell differentiation, eventually depleting the self-renewing source of hair-color cells and leaving the mice with gray coats.
The scientists suggest that accumulated DNA damage in long-lived stem cells may cause symptoms of aging, with gray hair being the most visible one. But they also ask whether a stem-cell quality control mechanism that keeps defective stem cells from replicating might also protect against cancer.
BOTTOM LINE: Stress at the cellular level damages hair follicles in mice, leading to gray hair through a protective mechanism that stops hair-color stem cells from renewing themselves.
CAUTIONS: The study looked only at stem cells in hair follicles, and only in mice.
WHAT'S NEXT: Further experiments could explore whether stem cell differentiation is a common quality control mechanism that animals, including humans, use to prevent damaged cells from causing disease.
WHERE TO FIND IT: Cell, June 12, 2009
ELIZABETH COONEY
How to stay sharp
Seniors with at least a high school education who exercise regularly, volunteer, and don't smoke have a better chance of maintaining mental fitness than other people 70 and older, according to a new study.
Researchers at the University of California-San Francisco tracked the cognitive function of nearly 2,500 men and women who were between the ages of 70 and 79 when the project began. While the majority of participants - 53 percent - showed normal age-related cognitive loss after eight years, 30 percent reported no cognitive decline.
Trying to figure out what gave these elders an advantage over the others, the researchers found that, in addition to regular exercise, having a high school education and at least a ninth-grade literacy level, living with someone, and holding down a job or volunteer duties dramatically increased one's ability to maintain normal cognitive function.
Previous research suggests that interacting with others through work or volunteerism keeps seniors engaged - emotionally and neurologically. People who are educated often "keep learning and have greater plasticity of neurons even in old age," says Kristine Yaffe, a professor of psychiatry, neurology, and epidemiology and lead author of the paper.
Surprisingly, conditions such as diabetes and hypertension had no impact on whether a senior kept or lost cognitive function.
BOTTOM LINE: A healthy and engaged lifestyle can help keep seniors mentally sharp as they age.
CAUTIONS: The study excluded seniors with cancer and other serious health problems, meaning that the findings can't be generalized to the larger public, says Hugh Hendrie, professor of psychiatry at the Center for Aging Research at Indiana University. What's more, there could be other factors involved in seniors maintaining cognition that this observational study didn't detect.
WHERE TO FIND IT: Neurology, June 9, 2009
KELLI WHITLOCK BURTON 