If you could prolong your life by a few more years (or even live to be 100), would you do it? I can't think of many people who would say no.

I've devoted my entire career to geriatrics, a field that specializes in the care of older adults. I helped start one of the first geriatrics programs in the U.S. at Harvard Medical School, and I'm currently a professor of medicine and public health at Brown University.

Having been a geriatrician for 55 years, the one question I'm constantly asked by folks of all ages is, "What are the most important everyday habits that can lead to a longer, more vibrant life?" I've given a lot of guidance on this to my patients, and I've seen positive results in people who follow them, including myself.

I celebrated my eightieth birthday this year, and I'm still going strong. I feel about as healthy and sharp as I did a decade ago. (Even my medical school interns don't stand a chance at beating me in squash, a sport I play several times a week.)

At 80, I've outlived the average American's life expectancy, which, for the first time in 100 years, has been on the decline. In 2014, our anticipated lifespan was 78.9 years, according to the Centers for Disease Control and Prevention. In 2017, it dropped to 78.6 years.

If you ask me, the biggest drivers are obesity, physical inactivity, smoking and substance abuse.But the good news is that it's never too late to change your lifestyle.

Here are some of the simplest things you can do nowto increase your chances of living a longer, healthier life:

I believe in the power of a Mediterranean-like diet (think: a combination of Italian and Greek dishes).

According to theDietary Guidelines for Americans, this plant-based diet filled with fresh fruits and vegetables, whole grains and healthy fats can help prevent chronic disease and promote overall health.

I like to think of the Mediterranean diet as more of a lifestyle routine than a strict plan you follow for a while and then abandon, because it can be hard to keep up with. Want a T-bone steak every month? Go for it! But try to avoid processed and fast foods. Include seafood, lean meats and nuts in your meals instead.

Fatty fish, such as salmon, sardines and albacore tuna, are staplesfor a goodMediterraneandiet. They're rich omega-3s, which research shows can help reduce your risk of heart disease and stroke. The American Heart Association recommends two 3.5-ounce servings of fish (particularly the fatty kind) weekly.

Extra-virgin olive oil, another staple of the diet, canhelp prevent heart attacks, stroke and cardiovascular death, even among people at higher risk.

Studies have shown that obesity and physical inactivity are two of the biggest contributors to diseases and a shortened lifespan. Fight back with exercise, which not only improves physical function, but also helps reduce the risk fordepression,canceranddiabetes.

TheAmerican Cancer Societyrecommends two and a half to five hours of moderate physical activity (e.g., walking, gardening) a week, or one to two and a half hours of vigorous physical activity (e.g., running, aerobics) a week.

I gravitate toward squash and anything else that gets my heart and respiratory rates up. But just 30 minutes of walking every day can make a difference.

Start moving now and keep it up. It can help add years to your life.

As everybody already knows, smoking has deadly consequences. It can cause health issues like heart disease, cancer, lung disease and emphysema, among many others. Research shows that even "light smoking" (as little as one cigarette a day) can greatly increase your risk of dying early.

But the benefits of quitting smoking start pretty quickly. The risk for a heart attack drops sharply just one year after quitting, according to the CDC. And, after two to five years, the chance of stroke could fall to roughly the same as a non-smoker.

Another thing: Don't be fooled into thinking vaping is a healthier alternative. Although there's limited research on the long-term effects of vaping, a recent study found that using e-cigarettes damages arteries in the same way that traditional cigarettes do.

Preventive care can help uncover health issues early, so schedule wellness exams as often as your health care provider recommends.

Some of the most important screenings and exams include cholesterol, blood pressure, skin cancer, and breast and cervical cancer for women (pap smears begin at age 21, mammograms start at 40). Depending on your family history, your doctor may suggest others.

Keeping up with these annual visits is a chance to review your lifestyle choices (e.g., diet, exercise habits, smoking status, alcohol use) and common behavioral health problems (e.g., stress, anxiety, depression). It's also an ideal time to talk about specific screening tests that you probably never even knew about.

You can discuss with your doctor the benefits and risks of certain tests or vaccinations to help make a shared decision about whether or not you want to have them. The key is to stay better informed and engaged about your ongoing health.

I can't stress enough the importance of protecting your mental health.Studiesshow that having a major mental illness can shorten your lifespan by 14 to 32 years

If you're concerned, ask your general physicianto give you amental health assessment, which can help pinpoint problems.

Also, make time for stress relief activities, such as meditation and yoga. Engaging in meaningful hobbies and connecting socially with other people can have a powerful influence on your mental well-being and happiness.

It may be hard do some of these things during a pandemic (and with social distancing orders in place), but don't underestimate the power of video calls with friends and relatives; seeing people, even on a small screen, can be emotionally rewarding.

Richard W. Besdine, MD, is a Professor of Medicine and Health Services Policy and Practice at Brown University.He is a member and former president of theAmerican Geriatrics Society.Dr. Besdine has authored more than 125 scholarly publications on aging, and trained in internal medicine, infectious diseases and immunology at Boston's Beth Israel Hospital and Harvard Medical School.

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An 80-year-old doctor and longevity expert shares his 5 habits for a longer life: 'It's never too late to start' - CNBC