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If during this holiday season you saw or read that Dr. Seuss classic "How the Grinch Stole Christmas," you'll recall how his heart grew three sizes the day he finally started thinking of others. Maybe that's the explanation for the surprising news last week that a person who cares for an aging loved one may be significantly extending his or her own life: A bigger heart.

Actually that's my own interpretation, but it may be close to the truth.

The study:

University of Michigan researchers tracked seven years of data on 1,688 couples over 70 who were living on their own (not in assisted living). Even after controlling for age, gender, economic status, or prior illness, spouses who cared for their mates at least 14 hours a week had a 36 percent lower risk of dying than those whose mates required no care.

The explanation:

Researchers do, in fact, credit some kind of physiological response. They theorize that helping someone may release oxytocin, a hormone that buffers the stress response. Chronic stress, of course, elevates the heart rate and blood pressure, among other effects, and puts one at risk for a host of life-threatening disorders, especially heart disease.

The takeaway:

This research is a reassuring note amid the usual steady drumbeat of warnings that caregivers are at higher risk for stress and depression. They are. But there are known ways to lower those risks. This study is a reminder that caregiving isn't all negative; it can confer protective health benefits, too.

There's one more aspect of caregiving that's theorized to help extend caregivers' health: Having a partner to care for also provides structure and a sense of purpose.

So is caregiving a burden, or a lifesaver -- or both?