Human health is the ultimate crapshoot. Mother Nature packs about 20,000 genes into every chromosome in each cell in our bodies, and some of us get high cholesterol and nearsightedness, while others get clear arteries and 20/20 vision.

But the relationship between DNA and health is complex. For some conditions, such as early-onset Alzheimer’s disease, the link is brutally clear. If one of your parents has it, the odds are 50-50 that you’ll get it, too. Other connections are murkier. People born with certain genes linked to obesity are between 20 and 30 percent more likely to be obese. Looked at another way, though, those same folks are 70 to 80 percent as likely not to be obese and are able to dodge the disorder by eating well and exercising often.

The upshot? Much of the time, family history is not destiny. Lifestyle tweaks can change your genetic makeup to prevent or delay illness. In fact, the simple act of taking charge of your genetic destiny is likely to improve your health, says Margie Lachman, a health psychologist at Brandeis University in Waltham, Massachusetts. The secret is maintaining a sturdy sense of control while acknowledging that health is about probabilities, not promises. “Someone can do everything right and still get a devastating disease,” Lachman says. We found seven health heroes striving to rewrite their family health history.

Jose Cortez (Type 2 Diabetes)

Who’s got it: About 29 million Americans, including 1 in 4 people 65 or older, says the American Diabetes Association.

Family risk: Type 2 diabetes has a strong genetic component. If both parents have the disease, you have a 1 in 2 chance of developing it. If just one parent has it, your risk is 1 in 7.

Jose Cortez isn’t just fighting his family’s diabetes; the disease has turned him into a road warrior.

Now 68, the retired public relations manager from Phoenix was diagnosed seven years ago. “I knew there was something wrong,” he says. “I didn’t feel good.” He was overweight and stressed out. Still, when his doctor told him he had both diabetes and high blood pressure — two disorders linked to coronary disease — he was surprised. “I remember saying, ‘Are you sure?’ And the doctor told me that my glucose reading, which should be under 125, was over 500. He said, ‘ You’re ready for a heart attack!’ ”

Initially, the news leveled him, and he had to acknowledge he had

inherited the family denial as well as diabetes: “My mother died of diabetes when I was in my 20s, and we found her medication — never taken — after she passed away.”

But the diagnosis turned out to be the wake-up call Cortez needed. He knew that work caused much of his stress, so he decided to retire early. “We knew it would be hard financially, but I came to the conclusion that my health was more important,” he says. And as an activist in the Chicano community, he also had to own up to the cultural risks facing his family. Hispanics have higher rates of diabetes than non-Hispanic Caucasians, and the risk is particularly high for those of Mexican descent.

Loaded up with medication to lower his glucose levels and his blood pressure, Cortez also cut back on fried foods and soda, replacing them with fruits, vegetables and plenty of water. And he started walking. Then he felt good enough to run. “First it was one mile, then it was two. Pretty soon I was up to 10Ks, then marathons,” he says. Cortez’s biggest adventure yet will be the six-month Peace and Dignity Run, from Alaska to Panama.

Despite his personal progress — he has lost 50 pounds and takes very little medication — he is still dismayed by the widespread diabetes in his family; his mother’s brother and one of his sisters have the disease. His job, he figures, is to set a good example.

As for his own demise, he says, “I envision myself being a 110-year-old grandpa and just not opening my eyes one day. The creator has a job for me, and when he is ready to take me — after many more miles to run, I hope — I think it will be in a quiet way.”

The upshot: When he was diagnosed, Cortez’s glucose level was over 500, and his blood pressure was 163/99. Through weight loss, diet changes, exercise and meds, his glucose levels are between 115 and 130, and his BP is 130/65.

Daniel Lukasik (Depression)

Who’s got it: Nearly 14.8 million people in the U.S. have depression; some 43,000 commit suicide each year, with men in midlife at highest risk, according to the American Foundation for Suicide Prevention.

Family risk: Having one parent with major depression or another mood disorder makes people two to three times more likely to develop depression. If both parents have a mood disorder, the risk rises to five times higher than average.

Growing up in Buffalo, New York, Daniel Lukasik always knew his family was different. He just wasn’t sure why. “I could see how neighbors played with their kids,” he says, “but things were bad at our house. My father drank heavily. My mom watched a lot of TV and ate all the time.” When he was 10, recalls Lukasik, now 54, his father would disappear for in-patient psychiatric treatment, coming home with plenty of pills but no solution.

It wasn’t until his own depression hit at age 40, though, that he began to grasp how paralyzing mental illness could be. “I cried often,” he reveals. “But it wasn’t cathartic. I never felt better after. I lost interest in things. Worst of all, I lost the ability to concentrate — I was a partner in a law firm, and I just couldn’t focus.”

His depression was so debilitating that his psychiatrist urged him to take a six-week leave from work, and he started the rough road to recovery, including therapy and medication.

Since then, he’s assembled what he calls his depression tool kit. Helping others was the first step, and he started a blog for lawyers with depression. “That’s given my life a great deal of meaning and connected me with hundreds of other people,” he says. A support group has also been important, and he’s had the same therapist, off and on, for 10 years.

Awareness of the genetic impact — not just of depression but the alcohol and drug abuse that so often accompany it — has been key as well. “My family tree is just littered with it,” he says, so he makes it a point to talk with family, especially his 16-year-old daughter, about his struggles.

But by far his most effective tools are exercise and spirituality. For the first, he relies on workouts three or four times a week — a rigorous 30 minutes on the elliptical machine, followed by weight training, which buoys his mood for 12 to 16 hours. And for the second, he’s come up with his own mix of Catholicism and Buddhism. “After a point, analyzing why I’m depressed isn’t useful. Mindfulness helps me just accept it,” he says.

The upshot: His first episode of depression was, he says, “a 10 out of 10. But because of the skills I’ve learned, my depressions now are shorter and not as deep. The worst it gets is a 5. Most days, I’m at 1.”

Lisa Lee-Ranson (Heart Disease and Stroke)

Who’s got it: Approximately 85.6 million Americans have cardiovascular disease, which includes heart attacks, arrhythmia, stroke and atherosclerosis, notes the American Heart Association.

Family risk: More than 100 different genes play some role in heart health.

When she was in her 30s, Lisa Lee-Ranson, of Dunbar, West Virginia, thought she knew all about heart disease. She had watched her dad suffer through a heart attack, followed by surgery for a sextuple bypass. Yet when she felt a burning sensation in her chest during tennis lessons, she kept dismissing it as acid reflux.

Finally, she went to see her doctor, who ordered a stress test. Instead of leaving with a warning to lose a little weight or cut down on her beloved cheese, Lee-Ranson was scheduled for immediate surgery: “I was only 34 years old, but I needed a double bypass. I had 90 and 99 percent blockages. I was the youngest person they had ever seen.”

The family history added angst to the crisis. “I remember watching my dad cry in the hospital,” she says. “He felt so responsible.”

Lee-Ranson, who is now 52, responded by making big changes. She dropped from 160 pounds to 135 (she is 5 foot 4). “I take multiple medications to control my cholesterol and get all my regular checkups. We eat a lot of chicken. I have some form of oats and an apple every day. No caffeine, because it gives me palpitations. And while it isn’t easy for me to stay active, I try to walk with neighbors regularly.”

She believes, though, that her most powerful protection comes from “major prayer,” which she does for about 15 minutes each morning and then as needed throughout the day.

Prayer and meditation are proven stress reducers, but they have also given her time to contemplate. “I know I have to die of something, and given our history, it may well be heart disease,” says Lee-Ranson, a project manager for the Charleston Area Medical Center. “But I figure, as long as I am here, why not make it the best it can be?”

The upshot: Before surgery, Lee-Ranson’s total cholesterol level was 350. These days, thanks to medication, diet and exercise, it is below 141.

Teppi Jacobsen (Breast cancer)

Who’s got it: Between 5 and 10 percent of breast cancer cases — about 23,000 a year — are caused by mutations in genes known as BRCA, according to the nonprofit advocacy group

Family risk: While the BRCA mutation is rare, it’s powerful: Women who carry it run a 45 to 65 percent lifetime risk of developing breast cancer, plus a higher risk of getting ovarian cancer. Men with the gene have a higher risk of developing breast cancer and prostate cancer.

When Teppi Jacobsen was 45, she found a lump in her right breast that was quickly diagnosed as a triple-negative malignancy, which is one of the most aggressive forms of breast cancer. She had a lumpectomy, 16 rounds of chemotherapy and 35 radiation treatments: “I lost my hair. I gained a bunch of weight. But I was alive, so I was happy.”

Jacobsen, who owns a women’s accessories business in Lincolnshire, Ill., continued to see her oncologist for screening for the next 10 years. “But even though I had a strong family history of cancer, even though I’d had the type of cancer that suggests a BRCA defect, and even though I’m Jewish, genetic testing never came up.”

Then in June 2013, a mammogram revealed a pea-size lump, this time in her left breast. Besides having a needle biopsy, which revealed that this, too, was a triple-negative tumor, she got tested for the BRCA gene and found out she was positive. That meant her odds of getting breast cancer a third time were great, as was the likelihood of developing ovarian cancer. The surgeon recommended a double mastectomy and having her ovaries removed also, which she did several months later. “I had to give the mastectomy a lot of thought,” she acknowledges.

But for Jacobsen, the worst angst hasn’t been about her own history. Her two daughters, 26 and 28, have tested positive for the BRCA gene, as has her sister.

“It terrifies me,” says Jacobsen, now 58, “and I know it frightens my girls.” But knowledge is power. Both her daughters have had MRIs and undergo stepped-up screening.

The upshot: Jacobsen is free of the disease.

Tonya Dennis and Roland Cooper (Colorectal Cancer)

Who’s got it: Colorectal cancer is the third most common cancer in the U.S., and the second most deadly, with about 137,000 people diagnosed each year, according to the Colon Cancer Alliance.

Family risk: People with a close relative who has had colon cancer are up to three times as likely to develop it themselves. African Americans have a 20 percent higher incidence rate and a 45 percent higher mortality rate.

A routine colonoscopy didn’t just save Tonya Dennis’ life. It may have saved her brother’s life, too. Their grandmother had been diagnosed with colon cancer while in her 60s, and Dennis always noted this on her family history at medical appointments. But it wasn’t until a routine OB-GYN checkup in her mid-40s that a doctor finally questioned why she had never had a colonoscopy.

“I told her I thought that started when I turned 50,” Dennis recalls. “She said, ‘No, all African Americans should start at 45’ — and even earlier if there was a family history.” Dennis, who lives in North Charleston, South Carolina, had her first colonoscopy a few months later, and when the physician called her in to discuss results, she wasn’t worried. “I was healthy. I figured I’d get a lecture about eating more fiber.”

Instead, she learned she had stage 3 rectal cancer. “It floored me,” says Dennis, who works in child protective services. “The tumor was very close to a wall and would soon have crossed into my other internal organs. And I had no symptoms at all. If it weren’t for that colonoscopy, I’d never have known.”

Amid the blur that followed — which included chemotherapy, radiation and surgery, with a temporary ileostomy, plus getting her older son off to college — she called her younger brother, the Reverend Roland Cooper, and insisted he get screened also.

Because he was having some serious heart problems, he dragged his feet for almost two years. But his colonoscopy revealed stage 2 colon cancer. While his case was less advanced, his surgery was far more dramatic: His heart stopped not once, but twice. “They told my wife they thought I’d have brain damage,” says Cooper, who works in security in public schools and is on the ministerial staff at his church. “It’s a miracle that I’m here today.”

Both Dennis, currently 51, and Cooper, 49, now eat more healthfully, with more chicken and fish and less red meat. They try to be active, and each pushes their family members to be aware of screening guidelines. In addition, they are heavily involved in cancer-awareness outreach.

“We have to get this message out to people with a family history, especially in the African American community,” Dennis says. “So often, there are no symptoms. That’s why screening is everything.”

The upshot: Today, Dennis and Cooper are free of the disease.

While dodging diseases that plague your family tree requires a certain amount of good fortune, studies have shown that some health habits are rock solid for fending off multiple illnesses. Here are six to-do’s you can swear by, every day:

  • Take a deep breath — or 20. Simple mindfulness techniques boost healthy glucose levels, improve cardiovascular health and help with anxiety and depression.
  • Get moving. Exercise really is the wonder drug, reducing the risk of Parkinson’s disease, heart disease and diabetes, as well as improving mood and cognitive ability.
  • Say no to sweets. Everyone knows that too much sugar leads to weight gain, but more than 25 grams (6 teaspoons) per day is also linked to inflammation and such health risks as breast cancer, heart disease, diabetes and, of course, obesity. (The typical American consumes as much as 20 teaspoons of sugar a day.)
  • Eat less meat and more produce. Meat has been linked to higher rates of many cancers, heart disease and diabetes.
  • Spend time with friends. Strong social ties protect people from heart disease, high blood pressure and depression, and may help stave off Alzheimer’s disease. (Just 10 minutes of socializing a day is enough to improve cognitive performance.)
  • Sleep at least seven hours per night. Inadequate zzz’s have been linked to diabetes, cardiovascular disease, obesity and depression. —S.M.