12 Surprising Signs You'll Live to 100 [1-6]

You're the life of the party.

Outgoing people are 50 percent less likely to develop dementia, according to a recent study of more than 500 men and women age 78 and older from the Karolinska Institutet in Sweden. Participants also described themselves as not easily stressed. Researchers speculate that their more resilient brains may be due to lower levels of cortisol—studies show that oversecretion of this "stress hormone" can inhibit brain cells' communication. Science-backed ways to cut cortisol levels: Meditate, sip black tea, or take a nap.

You run for 40 minutes a day.

Scientists in California found that middle-aged people who did just that—for a total of about five hours per week—lived longer and functioned better physically and cognitively as they got older; the researchers tracked runners and nonrunners for 21 years. "What surprised us is that the runners didn't just get less heart disease—they also developed fewer cases of cancer, neurologic diseases, and infections," says study author Eliza Chakravarty, M.D., an assistant professor of medicine at Stanford University School of Medicine. "Aerobic exercise keeps the immune system young." If you don't like to run, even 20 minutes a day of any activity that leaves you breathless can boost your health, she says.

You like raspberries in your oatmeal.

Most Americans eat 14 to 17 g of fiber per day; add just 10 g and reduce your risk of dying from heart disease by 17 percent, according to a Netherlands study. Dietary fiber helps reduce total and LDL ("bad") cholesterol, improve insulin sensitivity, and boost weight loss. One easy fix: Top your oatmeal (½ cup dry has 4 g fiber) with 1 cup of raspberries (8 g) and you get 12 g of fiber in just one meal.

Try some of these other potent fiber-rich foods: ½ cup of 100 percent bran cereal (8.8 g), ½ cup of cooked lentils (7.8 g), ½ cup of cooked black beans (7.5 g), one medium sweet potato (4.8 g), one small pear (4.3 g).

You feel 13 years younger than you are.

That's what older people in good health said in a recent survey of more than 500 men and women age 70 and older. "Feeling youthful is linked to better health and a longer life," says researcher Jacqui Smith, Ph.D., professor of psychology at the University of Michigan. "It can improve optimism and motivation to overcome challenges, which helps reduce stress and boost your immune system and ultimately lowers your risk of disease."

You have a (relatively) flat belly after menopause.

Women who are too round in the middle are 20 percent more likely to die sooner (even if their body mass index is normal), according to a National Institute on Aging study. At midlife, it takes more effort to keep waists trim because shifting hormones cause most extra weight to settle in the middle. If your waist measures 35 inches or more (for men, 40 inches or more), take these steps:

Work two or three 20-minute strength-training sessions into your weekly exercise regimen to preserve lean muscle mass and rev metabolism.
Eat a daily serving of omega-3s to help combat inflammation and seven daily servings of fruits and vegetables, loaded with disease-fighting antioxidants.
Get 25 percent of your daily calories from healthy fats—such as monounsaturated fatty acids—which protect your heart and may help you store less fat in your belly (for a 1,600-calorie diet, that's 44 g).

You get your blood tested for vitamin D levels.

For optimal disease protection, we need at least 30 nanograms of vitamin D per milliliter of blood, reports a study in the Archives of Internal Medicine. Nearly 80 percent of Americans have less than that. Vitamin D not only helps bones ward off osteoporosis but may also reduce your risk of cancer, heart disease, and infection, says lead researcher Adit A. Ginde, M.D., M.P.H., an assistant professor of surgery at the University of Colorado Denver School of Medicine. If needed, you can take a daily supplement to get your numbers up. Doctors can measure your levels with a simple blood test, but periodic monitoring may be necessary—vitamin D turns toxic at 100 to 150 ng/mL.