5 Surprising Things That Age You

What they age: Your cells

The science: A startling discovery comes via a study in Biological Psychiatry, which reported that women with five key symptoms of insomnia were almost two years older biologically than women of the same age without sleep issues. (The insomnia symptoms were difficulty falling asleep, restlessness, waking up during the night, trouble dozing off again and waking up too early.) This study didn't show a cause-and-effect relationship, but study author Steve Horvath, PhD, a professor of human genetics and biostatistics at UCLA's David Geffen School of Medicine, notes that it's still good reason not to let sleep issues linger.

What you can do: Treat the insomnia. If you're having trouble sleeping, or notice any of the five symptoms above, ask your doctor for help.