Answer by Katherine Killoran, physician and cancer survivor, on Quora

Establishing healthy habits is a good start. When you feel well, it’s easier to be happy and successful and get the most out of life. Often diet and exercise are the first things that come to mind when thinking of healthy habits. There is an avalanche of opinions on what a healthy diet is. I think it depends on our individual personal preferences as well as our metabolism. But whether your diet is vegan, vegetarian, paleo, Mediterranean, or labeled something else, it comes down to real food. Cook for yourself with quality ingredients and eat at home, enjoy your food, and if possible, share with others. You will undoubtedly be healthier and happier.

I always thought I had a reasonably healthy diet until I was diagnosed with cancer and considered more carefully what I was eating. I feel better and am happier when I eat real food that I cook at home. Maybe it’s age; maybe it’s because I am more aware, but my body lets me know when I don’t eat well. I do enjoy cooking and strive to eat a wide variety of vegetables every day. I think most of the food we cook at home is delicious, so I am not sacrificing anything to eat well.

Get some exercise. Exercise reduces depression and increases pain tolerance. Do it outside if you can. Being outside makes you happier and also helps reduce depression and anxiety. Make sure it is an activity that you like. The more it feels like work, the less beneficial it is for you and the less likely you are to do it. Sweat. The harder you work, the less time you need to put in.

I am an exercise addict. I tend to go overboard. I can count the days during chemotherapy that I did not exercise on one hand. It, for sure, helped me feel better during a time when feeling crappy was the norm. I continue to enjoy being active and have added high-intensity intervals to my various activities–swimming, biking, running, and lifting weights. It’s hard to know for sure, but I am confident it has improved my speed, strength, and overall level of fitness.

Sleep. While not everybody needs a full eight hours of sleep every night, most people need more than six. No surprise, when you are well rested, you think and perform better, which helps you accomplish more and be happier and more successful.

Stress and lack of sleep were major issues for me. One week after I was diagnosed with cancer, when my priorities were put in place by necessity, I was sleeping better than I had in several years. I think anxiety and lack of sleep contributed to my diagnosis in the first place. But even with a recent cancer diagnosis, better sleep helped me on the road to a happier life.

Yeah, yeah, yeah–diet, exercise, and sleep, everyone knows that. However, it’s your relationships that may be the most important. At least that’s the conclusion from the Harvard study of adult development. This study started in the 1930s and is still going on today, more than 75 years later. It followed 724 men from very different backgrounds. One group was composed of Harvard students, and the other was poor, underprivileged boys from Boston’s inner city.

Some of the original participants are still alive today in their 90s, and the study is now following the children from the initial group. This study tracked these men, interviewing them, reviewing their medical records, and talking to their wives and families to determine what factors resulted in health, happiness, and longevity. It wasn’t money, success, or a healthy cholesterol level at age 50 that best predicted good health and happiness at age 80. Instead, it was how satisfied the men were with their relationships. Being more socially connected to family, friends, and community led to happier, healthier people who lived longer. Robert Waldinger is the current director of the study; you can listen to his TED talk here.

Another example of the remarkable power of relationships and community on health and longevity is known as the Roseto effect. Roseto is a small town in northeastern Pennsylvania. In the 1960s, a local doctor realized there was an exceptionally low rate of heart disease in Roseto–it was virtually nonexistent compared with some of the surrounding towns.

The inhabitants smoked cigars, drank lots of wine, and ate meatballs, sausage, and plenty of cheese, while being exposed to potentially toxic gases and dust in the slate quarries. Not exactly the usual recipe for good health.

However, the community was very close-knit. There was no crime; people supported each other, and meals were a reason to get together and celebrate. There was a strong work ethic, with everyone in town working toward a similar goal: a better life for their children. Their children did go on to have more material things and traditional success, but not necessarily better lives. As the supportive community began to break down, the rates of heart disease and premature death increased, equaling the rates of the surrounding towns.

The people of Roseto were Italian immigrants. Their lifestyle, with an emphasis on close, supportive relationships, appears to have protected them from chronic disease and is similar to the way of life along the Mediterranean. The Mediterranean diet is considered to be one of the healthiest in the world. A British cardiologist,  Aseem Malhotra, is making a film about Pioppi, Italy, called The Pioppi Protocol. Pioppi is on the Mediterranean, and its inhabitants are among the world’s healthiest, often living into their 90s. In his film, Malhotra contends that it is the Mediterranean lifestyle, not just the diet, that cultivates good health, happiness, and longevity. People eat well, and savor and enjoy their food. They are social and connected to their community. They spend time outside, moving and engaged in activities they enjoy.

Take care of yourself. Eat well. Move daily. Get enough sleep. Maintain and nurture your relationships. In doing so, you will inevitably increase your energy and enjoyment from life. When you take care of yourself, not only do you have more energy (which will give you more time to focus on success), but you also feel well, so you are better equipped to enjoy the time you have.

I put together a daily wellness checklist to remind, motivate, and inspire me to achieve within each of these areas. Click here if you’d like a copy. It helps me stay on track and gives me a little win when I check off an activity as completed.

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Answer by Katherine Killoran, physician and cancer survivor, on Quora